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Hydrogen cycle
Like carbon, nitrogen, and phosphorus, there is also a cycle of hydrogen here on Earth. Hydrogen atoms move between biotic (living) and abiotic (non-living) sources.
Hydrogen (H) is the most abundant element in the universe.
On Earth, common H-containing inorganic molecules include water (H2O), hydrogen gas (H2), methane (CH4), hydrogen sulfide (H2S), and ammonia (NH3).
Organic compounds contain H atoms (as well as C.)
The chemistry of the Hydrogen cycle is highly relevant to the development of life on Earth and mostly likely elsewhere in space.
Hydrogen fuels rockets, but what about power for daily life? We’re getting closer. Phys.Org
Image from, Development and testing of new materials for high temperature PEM water electrolysis, Antonio Luis Tomas-Garcia
Where does our H2 come from? (sources)
biological processes in the oceans
biological (microbial) processes in soils
photochemical production in the troposphere via CH2O also written as H−CHO, formaldehyde.
Where does the H2 go? (sinks)
soil uptake
photochemical destruction in the troposphere by OH radicals
Free H2 can then be consumed by other microbes, oxidized photochemically in the atmosphere, or lost to space.
Cycling: H2 molecules usually exist within the atmosphere for 4 to 7 years before they get taken up in a soil sink.
Hydrogen production and leakage
As we develop hydrogen based industries, in what ways will we be producing, distributing, and using hydrogen? In what ways will hydrogen leak out into the atmosphere?
In the left column we see H2 production.
In the middle column we take into account the fact that once H2 gas is made, it needs to be distributed by trucks, ships, cargo trains, etc.
In the third column we see H2 being used by end-use customers.
Notice that in every step some H2 gas leaks out. Leaks are unintended, and unavoidable. We can minimize them but they will never be zero.
image from, Emission scenarios for a global hydrogen economy
Possible effect on ozone layer
“Increased atmospheric emissions of hydrogen will therefore inevitably lead to increased levels of water vapour in the stratosphere which will in turn lead to increased stratospheric cooling. This cooling may change the distribution of polar stratospheric clouds which play an important role in the formation of ozone holes and hence may delay the recovery of the ozone layer.”
A mitigating factor is that “The potential environmental risks from the hydrogen economy were found to be small in comparison with the environmental benefits. ” …. “the few available studies all point to the impact of large potential hydrogen leakages on the stratospheric ozone layer as being small”
– Hydrogen for Heating: Atmospheric Impacts – A literature review
Possible effect on global warming
Hydrogen gas indirectly acts as a greenhouse gas because it interferes with the global chemical reactions which control the methane levels and the formation of ozone.
Methane and ozone are the second and third most important greenhouse gases after carbon dioxide.
There is still much uncertainty about how much H2 gas would affect global warming, although the effect is currently considered to be very small.
– Hydrogen for Heating: Atmospheric Impacts – A literature review,
Possible effect on air quality
H2 is relatively inert. It offers almost no chemical reactivity with urban pollutants such as NOx, O3, SO2, CO, VOCs and suspended particulate matter. Thus it has no direct influence on urban air quality.
However, because of its reaction with hydroxyl radicals: OH + H2 → H2O + H it plays a weak role in the long-range transport of photochemical ozone. This may affect ozone levels in the lower atmosphere, although the effect is currently estimated to be very small.
Caution in relying on Hydrogen power
Using hydrogen as a source of power for vehicles certainly has its drawbacks—among them the cost and the inefficient use of energy—but researchers are now warning against hydrogen for another reason, The Guardian reports: scarcity and a subsequent dependence on fossil fuels….
“Hydrogen-based fuels can be a great clean energy carrier, yet their costs and associated risks are also great,” said Falko Ueckerdt, at the Potsdam Institute for Climate Impact Research (PIK) in Germany, who led the research.
“If we cling to combustion technologies and hope to feed them with hydrogen-based fuels, and these turn out to be too costly and scarce, then we will end up burning further oil and gas,” he said. “We should therefore prioritise those precious hydrogen-based fuels for applications for which they are indispensable: long-distance aviation, feedstocks in chemical production and steel production.”
The research, published in the journal Nature Climate Change, calculated that producing and burning hydrogen-based fuels in home gas boilers required six to 14 times more electricity than heat pumps providing the same warmth. This is because energy is wasted in creating the hydrogen, then the e-fuel, then in burning it. For cars, using e-fuels requires five times more electricity than is needed than for battery-powered cars.
text above from Researchers Warn Against Becoming Too Dependent On Hydrogen To Power Cars Elizabeth Blackstock, May 2021, Jalopnik
Using hydrogen fuel risks locking in reliance on fossil fuels, researchers warn Damian Carrington, 5/6/2021, The Guardian (UK)
Potential and risks of hydrogen-based e-fuels in climate change mitigation Falko Ueckerdt et al., Nature Climate Change volume 11, pages384–393(2021)
Hydrogen Production and Distribution Alternative Fuels Data Center, US Dept. of Energy,
Some critics of Hydrogen power
The government’s embrace of ‘clean hydrogen’ helps no one but the fossil fuel industry, Richard Denniss, The Guardian , 5/2/2021
External articles
Atmospheric researchers present new findingson the natural hydrogen cycle. CalTech
Assessing Leaks in a Global Hydrogen Infrastructure: Can it Perturb the Natural Hydrogen Cycle?
Leaked hydrogen fuel could have small negative effects on atmosphere
Hydrogen fuel could widen ozone hole
Global Environmental Impacts of the Hydrogen Economy
Hydrogen Effects on Climate, Stratospheric Ozone, and Air Pollution
Impact of a possible future global hydrogen economy on Arctic stratospheric ozone loss, with graphic
What Are The Pros And Cons Of Using Hydrogen To Generate Electricity?
The Hydrogen Hoax , The New Atlantis, by Robert Zubrin
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
References
Bas van Ruijven et al., Emission scenarios for a global hydrogen economy and the consequences for global air pollution, Global Environmental Change, Volume 21, Issue 3, 2011, Pages 983-994,
Hydrogen for Heating: Atmospheric Impacts – A literature review, BEIS Research Paper Number 2018: no. 21, Dept. for Business, Energy and Industrial Strategy, UK
Learning Standards
Next Generation Science Standards
HS-LS2-4. Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.
A Framework for K-12 Science Education Practices, Crosscutting Concepts, and Core Ideas (2012)
LS2.B: Cycles of Matter and Energy Transfer in Ecosystems
College Board Standards for College Success: Science
Standard ES.4 – Cycles of Matter and Energy: Matter on Earth is finite and moves through various cycles that are driven by the transformation of energy
LS.4.1 Matter Cycling – Students understand that matter is continuously recycled within the biological system and between the biological (biotic) and physical (abiotic) components of an ecosystem.
ESH-PE.4.2.2 Construct a graphical representation of the global carbon cycle (or the cycle of some other element or molecule), and use this representation to predict the effects of some environmental change (e.g., evolution of life, tectonic change, human activity) on carbon cycling (or the cycling of some other element or molecule).
Enduring Understanding 3A – Biogeochemical cycles are representations of the transport, transformation and storage of elements on a local, regional or global scale.
Birds
Definition of birds
Birds are a group of warm-blooded vertebrates
They are characterized by the presence of feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton.
Birds live worldwide; range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. There are about ten thousand living species.
Evolution of birds
Almost all dinosaurs went extinct about 65 million years ago (at the end of the Cretaceous Period), after living on Earth for about 165 million years.
Almost all branches of the dinosaur family tree died out, except for the branch with small feathered dinosaurs. That branch proliferated and developed into the birds that we know today.
Zina Deretsky, National Science Foundation. Air sac system of birds and of Majungasaurus.
This infographic is one way to show the relationship between various forms of dinosaurs.
It illustrates that today’s birds are the last remaining branch of the dinosaur family tree.
Image by Shawn Gould and Jen Christiansen, from How Dinosaurs Grew So Large—And So Small, John R. Horner, Kevin Padian and Armand de RicqlèS
Scientific American 293, 56 – 63 (2005)
Groups of birds
Raptors, also known as birds of prey, are birds that primarily hunt and feed on vertebrates, and that are large relative to the hunter.
Raptors have keen eyesight for detecting food at a distance or during flight, strong feet equipped with talons for grasping or killing prey, and powerful, curved beaks for tearing flesh.
The term raptor is derived from the Latin word rapio, meaning to seize or take by force.
In addition to hunting live prey, many birds, such as fish eagles, vultures and condors, eat carrion.
Condors are under vultures, in the order of Cathartiformes.
Notice that raptors, like reptiles, are not a true clade.
“There’s No Such Thing As Reptiles Any More – And Here’s Why”
Phylogeny of core landbirds modified from Mindell et al. (2018). The shaded box encompasses the raptorial grade (see text), within which we propose that all orders are considered raptors. Raptors as a group is paraphyletic and mostly share the raptorial lifestyle passed down from their single common ancestor.
Such grouping assumes then that the raptorial lifestyle was lost twice independently with the ancestors of both the Coraciimorphae and Passeriformes/ Psittaciformes clades.
Commentary: Defining Raptors and Birds of Prey
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Learning Standards
Benchmarks for Science Literacy, American Association for the Advancement of Science
Students should begin to extend their attention from external anatomy to internal structures and functions. Patterns of development may be brought in to further illustrate similarities and differences among organisms. Also, they should move from their invented classification systems to those used in modern biology… A classification system is a framework created by scientists for describing the vast diversity of organisms, indicating the degree of relatedness between organisms, and framing research questions.
Evolution and diversity: Origin of life, evidence of evolution, patterns of evolution, natural selection, speciation, classification and diversity of organisms.
Teaching About Evolution and the Nature of Science, National Academy Press (1998)
Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.
Zeroth law of thermodynamics
People normally think of the three laws of thermodynamics. But there is one idea that they all depend on, so basic that it often gets overlooked: the zeroth law.
This idea works like the transitive rule of algebra:
If A = B and B = C then A = C
If the temp of object A = temp of object B,
and the temp of object B = temp of object C,
then the temp of object A = temp of object C
Therefore all three systems would be in thermal equilibrium.
Let’s watch three different materials fulfill this law, by coming into thermal equilibrium.
Animation by Charles Xie
Thermal equilibrium (in this example) is reached when the temp of all pieces = 13.4 degrees C.
http://weelookang.blogspot.sg/2012/09/the-zeroth-law-of-thermodynamics.html
Also see https://www.grc.nasa.gov/www/k-12/airplane/thermo0.html
Another way to view this:
“When body A is placed in thermal contact with body B, there will be a flow of thermal energy between the two bodies. Thermal energy will flow from the body at a higher temperature, to the one at a lower temperature, until thermal equilibrium between the two bodies is reached.”
– Loo Kang Lawrence
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Measuring lengths in the metric system
In science and engineering we often have to make measurements of distances and lengths.
Here we’re going to get a feel what various distances would actually look like in real life.
Kilometers
Kilometers is abbreviated as km.
A km is 1,000 meters.
A km is 0.62 miles, or, you can say that one mile is 1.6 km.
How can we visualize this?
A kilometer is two and a half laps around a standard 400m track.
The 400-metre dash, is a sprinting event in track and field competitions.
This image from athleticsworld.net.
We can visualize a cube, 1 km wide, by 1 km long, by 1 km high, in the middle of New York City.
Here you can see this size compared to city streets, the Empire State Building, the Burj Dubai building, and central park.
Image from 7.3 Billion People, One Building, Tim Urban, waitbutwhy.com
meters
The meter is abbreviated as m.
What kind of things are about a meter long?
image from pxfuel.com
South Georgia College Tigers, Wikipedia
centimeter
Centi means 1/100th 0.01 10-2
The centimeter is abbreviated as cm.
It is one one-hundredth of a meter.
What kind of things are about a cm in length?
1 cm is the approximate width of average fingernail
3.5 cm is the width of film commonly used in motion pictures and still photography.
from How to load a 35mm Film SLR, ThePiece32
millimeters
milli means 1/1000th 0.001 10-3
This is 1/1000th of a meter.
What kind of things are commonly measured in millimeters?
A millimeter is about the thickness of a plastic id card (or credit card).
from mymetalbusinesscard.com
micrometers
A micrometer is abbreviated as μm
micro means 1/1,000,000th 0.000001 10-6
Just one one-millionth of a meter.
What kind of things are commonly measured in micrometers?
about as long as a Red Blood Cell
15 µm – width of silk fiber.
A single silk fiber could be roughly 100 times thinner than the smallest thread that you see here!
(You’d need 1000 fibers wound tightly together to create a thread of these sizes.)
17 µm – minimum width of a strand of human hair
Pollen, mold, plant spores: 7 – 70 μm
70 to 180 µm – thickness of paper
nanometers
Abbreviated as nm.
nano means 1/1,000,000,000 th 0.000000001 10-9
What kind of things are about a nanometer long?
Human fingernails grow about 1 nanometer per second.
Individual atoms are about 0.1 to 0.2 nanometers in diameter.
Here we see many atoms, each one of which is less than 1 nm wide.
image from dynamicscience.com.au
A single water molecule is about 1.5 nanometers.
A strand of human DNA is 2.5 nanometers in diameter.
A single hemoglobin molecule is 5 nanometers across.
A single bacterium is about 1,000 nanometers long.
Videos
Powers of Ten and the Relative Size of Things in the Universe
Computer apps
Powers of Ten (JAVA) For Windows and Macs. Check to see if this runs on Android phones or Chromebooks. Secret Worlds: The Universe Within: Molecular Expressions The size and scale of the universe htwins.net – scale of the universeSmartphone and tablet apps
Cosmic Zoom app by Tokata. For Android and iPad Google Play Store link About cozmic zoom Powers of Minus Ten, by Dynamoid Apps. iPad app thepartnershipineducation.com Powers-of-minus-ten Link for the Apple app storeThanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Learning Standards
Massachusetts Science and Technology/Engineering Curriculum Framework
Science and Engineering Practices: 5. Using Mathematics and Computational Thinking: Apply ratios, rates, percentages, and unit conversions in the context of complicated measurement problems involving quantities with derived or compound units (such as mg/mL, kg/m 3, acre-feet, etc.).
National Council of Teachers of Mathematics
Students need to develop an understanding of metric units and their relationships, as well as fluency in applying the metric system to real-world situations. Because some non-metric units of measure are common in particular contexts, students need to develop familiarity with multiple systems of measure, including metric and customary systems and their relationships.
National Science Teachers Association
The efficiency and effectiveness of the metric system has long been evident to scientists, engineers, and educators. Because the metric system is used in all industrial nations except the United States, it is the position of the National Science Teachers Association that the International System of Units (SI) and its language be incorporated as an integral part of the education of children at all levels of their schooling.
Measuring mass in the metric system
In science and engineering we often have to make measurements of mass. Now, I understand that a lot of American students have affinity for the traditional English system of measurements.
But we can’t make much progress in any field of science or engineering without first becoming conversant with the metric system. It is used worldwide.
How do we measure mass? To learn practical, hands-on skills, see our lesson here.
Measuring mass with a triple beam balance
But in this lesson we’re going to get a feel what various masses would actually look like in real life.
Kilograms
A kilogram is 1,000 grams. It is abbreviated as kg.
Can we convert between kilograms and pounds…. not quite [TBA]
But if all measurements are done here on Earth then 1 kg of mass has a weight of about 2.2 pounds.
Here’s a 1 kg steak dinner
image from TripAdvisor, Outback Steakhouse, Las Vegas Blvd
How can we visualize this? About the mass of a liter bottle of water or soda.
About the mass of good size hardcover book. About the mass of a quart of Gatorade.
Or about the mass of an adult Black-Footed Ferret.
Grams
A metric unit of mass is the gram abbreviated as g.
What kind of things are about a gram in mass?
Centigrams
Centi means 1/100th 0.01 10-2
A smaller metric unit of mass is the centigram abbreviated as cg.
It is one one-hundredth of a gram.
What kind of things are about a cg in mass? Many medications come in 1 cg size, although they more often are measured as 100 mg. Here are magnesium supplement pills.
When a pencil tip breaks, a bigger piece could be about 1 cg.
(We could name something that has a mass of gram and divide it in ten pieces)
milligrams
milli means 1/1000th 0.001 10-3
This is 1/1000th of a gram.
What kind of things are commonly measured in milligrams?
Many doses of medications are measured in milligrams:
Amitriptyline (Elavil) treats chronic pain and depression.
Atorvastatin (Lipitor) treats high cholesterol.
Amlodipine (Norvasc) treats high blood pressure and angina.
Here is crushed powder of a medication shown next to a penny for comparison.
Penny, 1 mg, 10 mg, 25 mg
Micrograms
Yet even smaller is the microgram abbreviated as μg
micro means 1/1,000,000th 0.000001 10-6
Just one one-millionth of a gram
What kind of things are commonly measured in micrograms?
Grains of sand are around 30 to 50 micrograms.
Mass of a grain of sand
Nanograms
Abbreviated as ng.
nano means 1/1,000,000,000 th 0.000000001 10-9
Imagine cutting a raisin into a billion pieces. Each of those tiny pieces has a mass of about one ng.
What kind of things are about a nanogram in mass?
A human cell or a grain of birch pollen. Note that in this picture, each dot that you can see is likely dozens of pollen grains stuck together.
Each individual grain by itself is so small that you’d need a microscope to clearly see it.
Nanograms are very small compared to anything we see in our daily lives, but they are large compared to a single atom
Chemistry math & mass problem
How many atoms of iron (Fe) are in 1 ng (1.0 x 10-9 g) of iron?
This problem from xaktly – Chemistry – The Mole.
We start by finding the molar mass of iron from the periodic table. It’s 55.85 g/mol.
We use the molar mass to convert to moles.
Then multiply by 6.022 x 1023 atoms per mole to get the number of atoms.
1 ng of iron atoms is about 1 x 10 ^ 13 atoms!
That’s 10,000,000,000,000 atoms.
Videos
Powers of Ten and the Relative Size of Things in the Universe
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Computer apps
Powers of Ten (JAVA) For Windows and Macs. Check to see if this runs on Android phones or Chromebooks.
Secret Worlds: The Universe Within: Molecular Expressions
The size and scale of the universe
htwins.net – scale of the universe
Smartphone and tablet apps
Cosmic Zoom app by Tokata. For Android and iPad
Google Play Store link
About cozmic zoom
Powers of Minus Ten, by Dynamoid Apps. iPad app
thepartnershipineducation.com Powers-of-minus-ten
Link for the Apple app store
Learning Standards
Massachusetts Science and Technology/Engineering Curriculum Framework
Science and Engineering Practices: 5. Using Mathematics and Computational Thinking: Apply ratios, rates, percentages, and unit conversions in the context of complicated measurement problems involving quantities with derived or compound units (such as mg/mL, kg/m 3, acre-feet, etc.).
National Council of Teachers of Mathematics
Students need to develop an understanding of metric units and their relationships, as well as fluency in applying the metric system to real-world situations. Because some non-metric units of measure are common in particular contexts, students need to develop familiarity with multiple systems of measure, including metric and customary systems and their relationships.
National Science Teachers Association
The efficiency and effectiveness of the metric system has long been evident to scientists, engineers, and educators. Because the metric system is used in all industrial nations except the United States, it is the position of the National Science Teachers Association that the International System of Units (SI) and its language be incorporated as an integral part of the education of children at all levels of their schooling.
Busting myths: No Virginia, some sugars aren’t better than others
Myth “Some sugars are better for our bodies than others.”
Myth “Natural, raw or unrefined sugars are better.”
Myth “It is better to use honey, maple syrup, agave syrup, or coconut sugar.”
Myth “Corn syrup is worse for us than other sugars”
Myth “Natural sugar is better than processed sugar.”
Reality: None of those claims are really true. In reality our metabolism breaks down all sugars the same way.
Agave syrup, maple syrup, coconut sugar – none of these are sugar alternatives – they are just sources of sugar.
Sucrose, a common sugar, is a disaccharide. That means it is a two-part molecule, made of glucose and fructose.
And get this – sucrose is not absorbed by the human GI tract. Instead, our intestines secrete an enzyme, sucrase-isomaltase.
This breaks down any sucrose into glucose and fructose, and it is those smaller sugars which are absorbed. So our body doesn’t care which kind of sugar we eat; the result is the same.
Image from sucraid.com/about-csid
Myth “Natural sugar is better than processed sugar.”
All sugars are processed. The so-called “processed” white sugar that people are afraid of is just sugar from a natural source, sugar cane or beets. Brown sugar? The same as white sugar, except that the molasses hasn’t been removed. Not healthier whatsoever.
“Raw honey” may be unprocessed, but it isn’t any healthier. It is just sugar mixed with water, pollen and a few other organic molecules. You’re not going to be helped by the microscopic amount of nutrients in raw honey unless you ate pounds of it a day.
Myth “High fructose corn syrup is worse for you than other sugar.”
Reality? Nope. It’s literally the same thing.
image from Examine.com, difference between HFCS and sugar
More details on this bit here – What is the difference between high fructose corn syrup (HFCS) and sugar?
Myth “Sugars higher on the glycemic index are worse for you.”
Nope. Such claims come from flawed studies, see below for details.
So, are we saying that sugar is good for you? No, we aren’t saying that either. Mainstream science already knows the answer, and people just refuse to hear it: For most people, having some sugar in our diet has always been fine. The problem comes from diets which have huge amounts of sugar, and not enough of other foods that actually are good for us.
While no one, single diet is best for everyone, science points to the same direction: Eat a balanced diet with whole grains, beans, legumes, vegetables and fruit. Have less meat, and certainly less processed meat. Eat far less fried foods. Watch your total calorie intake. Keep daily sugar and fat intake lower. There you go.
What’s wrong with those glucose versus sucrose studies?
In those studies, researchers did the following: They fed huge amounts of only one type of sugar molecule to one group of rats, and huge amounts of a different type of sugar molecule to another group of rats. Then they looked at how the health of the rats were affected over time.
Problem 1: These studies don’t resemble real world eating. Humans don’t spend entire days eating nothing but fructose or nothing but sucrose. The way that our metabolism would handle that is different from how it would handle normal eating, in which sugar is only a small part of the diet. In real life, even in poor diets, sugar is still only a fraction of the total: there are also proteins, complex carbohydrates, fats, oils, vitamins, minerals, etc.
Problem 2: Some studies attempted to see how consuming different sugars affects one’s resulting blood sugar level. Sugar molecules which create a higher result are said to be higher on a glycemic index; sugar molecules which create a lower result are said to be lower on the glycemic index. Yet these are unnatural diets in which rats ate only pure sugars. When we study the results of normal diets, with actual food, there’s almost no difference between sugars. A meal’s impact on resulting blood sugar levels depends on the amount of sugar and how fast it gets absorbed, not on the type of sugar molecule.
Problem 3: Rats do not metabolize sugars in the same ways that humans do. Hence, any inaccuracies due to the above problems become magnified, making the results non applicable to humans.
Result: The data from those studies are essentially useless.
Honors biology details
Glucose enters the glycolysis metabolic pathway at the top.
Here it is phosphorylated by Hexokinase.
Fructose enters glycolysis pathway two steps later, where it meets phosphofructokinase.
Thus, eating pure fructose allows the energy to be metabolized a bit faster than eating pure glucose.
But people don’t consume huge chunks of pure sugars. When eating anything resembling real life meals, the difference is very little.
Studies on High-fructose corn syrup (HFCS)
High-fructose corn syrup (HFCS) is also known as glucose-fructose, isoglucose and glucose-fructose syrup. There is no scientific evidence that HFCS itself causes obesity or metabolic syndrome, but rather overconsumption and excessive caloric intake of any sweetened food or beverage may contribute to these diseases.
Epidemiological research has shown that the increase in metabolic disorders, such as obesity and non-alcoholic fatty liver disease, is linked to increased consumption of sugars and calories in general.
A 2012 review found that fructose did not appear to cause weight gain when it replaced other carbohydrates in diets with similar calories.
A 2014 systematic review found little evidence for an association between HFCS consumption and liver diseases, enzyme levels or fat content.
The American Heart Association recommended that people limit added sugar (such as maltose, sucrose, high fructose corn syrup, molasses or cane sugar) in their diets.
High fructose corn syrup article
Is Sugar Really Toxic? Sifting through the Evidence
Scientific American Staff and Ferris Jabr, Scientific American, July 15, 2013
https://blogs.scientificamerican.com/brainwaves/is-sugar-really-toxic-sifting-through-the-evidence/
By consuming so much sugar we are not just demonstrating weak willpower and indulging our sweet tooth – we are in fact poisoning ourselves according to a group of doctors, nutritionists and biologists, one of the most prominent members of which is Robert Lustig of the University of California, San Francisco…
A few journalists, such as Gary Taubes and Mark Bittman, have reached similar conclusions. Sugar, they argue, poses far greater dangers than cavities and love handles; it is a toxin that harms our organs and disrupts the body’s usual hormonal cycles.
Excessive consumption of sugar, they say, is one of the primary causes of the obesity epidemic and metabolic disorders like diabetes, as well as a culprit of cardiovascular disease. More than one-third of American adults and approximately 12.5 million children and adolescents in the U.S. are obese. In 1980, 5.6 million Americans were diagnosed with diabetes; in 2011 more than 20 million Americans had the illness.
…. Because fructose metabolism seems to kick off a chain reaction of potentially harmful chemical changes inside the body, Lustig, Taubes and others have singled out fructose as the rotten apple of the sugar family. When they talk about sugar as a toxin, they mean fructose specifically.
In the last few years, however, prominent biochemists and nutrition experts have challenged the idea that fructose is a threat to our health and have argued that replacing fructose with glucose or other sugars would solve nothing.
First, as fructose expert John White points out, fructose consumption has been declining for more than a decade, but rates of obesity continued to rise during the same period. Of course, coinciding trends alone do not definitively demonstrate anything.
A more compelling criticism is that concern about fructose is based primarily on studies in which rodents and people consumed huge amounts of the molecule – up to 300 grams of fructose each day, which is nearly equivalent to the total sugar in eight cans of Coke – or a diet in which the vast majority of sugars were pure fructose. The reality is that most people consume far less fructose than used in such studies and rarely eat fructose without glucose.
…. Not only do many worrying fructose studies use unrealistic doses of the sugar unaccompanied by glucose, it also turns out that the rodents researchers have studied metabolize fructose in a very different way than people do—far more different than originally anticipated.
… Even if Lustig is wrong to call fructose poisonous and saddle it with all the blame for obesity and diabetes, his most fundamental directive is sound: eat less sugar. Why? Because super sugary, energy-dense foods with little nutritional value are one of the main ways we consume more calories than we need, albeit not the only way.
Glycemic index and obesity
Janette C Brand-Miller, Susanna HA Holt, Dorota B Pawlak, Joanna McMillan
Glycemic index and obesity, The American Journal of Clinical Nutrition
Volume 76, Issue 1, July 2002, Pages 281S–285S
https://doi.org/10.1093/ajcn/76.1.281S
Although weight loss can be achieved by any means of energy restriction, current dietary guidelines have not prevented weight regain or population-level increases in obesity and overweight. Many high-carbohydrate, low-fat diets may be counterproductive to weight control because they markedly increase postprandial hyperglycemia and hyperinsulinemia.
Many high-carbohydrate foods common to Western diets produce a high glycemic response [high-glycemic-index (GI) foods], promoting postprandial carbohydrate oxidation at the expense of fat oxidation, thus altering fuel partitioning in a way that may be conducive to body fat gain.
In contrast, diets based on low-fat foods that produce a low glycemic response (low-GI foods) may enhance weight control because they promote satiety, minimize postprandial insulin secretion, and maintain insulin sensitivity.
This hypothesis is supported by several intervention studies in humans in which energy-restricted diets based on low-GI foods produced greater weight loss than did equivalent diets based on high-GI foods.
Long-term studies in animal models have also shown that diets based on high-GI starches promote weight gain, visceral adiposity, and higher concentrations of lipogenic enzymes than do isoenergetic, macronutrient controlled, low-GI-starch diets.
In a study of healthy pregnant women, a high-GI diet was associated with greater weight at term than was a nutrient-balanced, low-GI diet.
In a study of diet and complications of type 1 diabetes, the GI of the overall diet was an independent predictor of waist circumference in men.
These findings provide the scientific rationale to justify randomized, controlled, multicenter intervention studies comparing the effects of conventional and low-GI diets on weight control.
Straight talk about high-fructose corn syrup: what it is and what it ain’t,
Straight talk about high-fructose corn syrup: what it is and what it ain’t,
John S. White, The American Journal of Clinical Nutrition
Volume 88, Issue 6, December 2008, Pages 1716S–1721S, https://doi.org/10.3945/ajcn.2008.25825B
High-fructose corn syrup (HFCS) is a fructose-glucose liquid sweetener alternative to sucrose (common table sugar) first introduced to the food and beverage industry in the 1970s. It is not meaningfully different in composition or metabolism from other fructose-glucose sweeteners like sucrose, honey, and fruit juice concentrates.
HFCS was widely embraced by food formulators, and its use grew between the mid-1970s and mid-1990s, principally as a replacement for sucrose. This was primarily because of its sweetness comparable with that of sucrose, improved stability and functionality, and ease of use.
Although HFCS use today is nearly equivalent to sucrose use in the United States, we live in a decidedly sucrose-sweetened world: >90% of the nutritive sweetener used worldwide is sucrose. Here I review the history, composition, availability, and characteristics of HFCS in a factual manner to clarify common misunderstandings that have been a source of confusion to health professionals and the general public alike.
In particular, I evaluate the strength of the popular hypothesis that HFCS is uniquely responsible for obesity. Although examples of pure fructose causing metabolic upset at high concentrations abound, especially when fed as the sole carbohydrate source, there is no evidence that the common fructose-glucose sweeteners do the same.
Thus, studies using extreme carbohydrate diets may be useful for probing biochemical pathways, but they have no relevance to the human diet or to current consumption. I conclude that the HFCS-obesity hypothesis is supported neither in the United States nor worldwide.
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Plant identification apps
Learning objectives
SWBAT (“students will be able to,” content, procedures, skills)
Describe characteristics of seeds and plants, based on observation.
Identify characteristics that are the same or different across various seeds and plants.
Use a dichotomous key
Vocabulary objectives
Tier II: Classify, Differentiate, Analyze
Tier III: Dichotomous key, bryophytes, vascular, seed, confiers, angiosperms, gymnosperms, monocotsm dicots
Connections
Life is classified in kingdoms; that plants are one of the many kingdoms; that this kingdom itself is broken down into many smaller groups. Students should be able to recognize what a plant looks like, and have the prior knowledge that plants need sunlight, space and water to survive.
Why identify plants?
Students should be able to explain several ways that plants are useful.
Answers might include:
Large scale food production
Local, community and home food production
Managing national and state parks
Necessary for a healthy ecosystem (biodiversity)
Necessary for human psychological health (contrast blighted areas with plant, tree and flower-rich yards.)
Biology, Miller and Levine, Chap 4, Pearson.
Use of plants in managing wildlife
From Noble News and Views:
“As natural resource managers, we must understand what we manage, and plant identification is a key component of that understanding.”
“whether you are a cow-calf producer, sheep and goat producer, wildlife manager, or manager of some combination of these enterprises, you should be paying close attention to what your management decisions are doing to the resources that support your enterprises: plants. After all, plants are what produce these products.”
“The ability to know, or identify, plants allows us to assess many important rangeland or pasture variables that are critical to proper management: range condition, proper stocking rates, forage production, wildlife habitat quality, and rangeland trend, either upward or downward.”
Noble.org – Plant-identification-is-it-worth-the-effort
Why use dichotomous keys?
Students often learn how to identify plants with dichotomous keys. This is a math and logic skill, valuable for classifying all forms of life (and any kind of classification system.)
A dichotomy is a partition of a whole (or a set) into two parts. This is an essential part of mathematical logic
The use of a dichotomous key for identification is an algorithm.
Apps
iNaturalist – https://www.inaturalist.org/
“Naturalist helps you identify the plants and animals around you. Get connected with a community of over 400,000 scientists and naturalists who can help you learn more about nature!”
PictureThis – https://www.picturethisai.com/
Helps more than 30,000,000 users identify, learn, and enjoy all kinds of plants: flowers, trees, succulents, cacti and more! Capable of identifying 10,000+ plant species.
Plantix – https://plantix.net/en/
Are you a farmer or hobby gardener and grow vegetables, fruit or arable crops? Are your plants sick; did you have losses in the last harvest? We are Plantix and offer you fast and free help. Whether you grow tomatoes, bananas or rice – Plantix is your interactive plant doctor. “
PlantNet Plant Identification https://plantnet.org/en/
This is a research and a citizen science project. Works on more than 20,000 wild plants, and ornamental and cultivated plants
Google Lens https://lens.google.com/
An image recognition technology developed by Google. Brings up relevant info about objects that it identifies using visual analysis based on a neural network.
External resources
Classification and dichotomous key worksheet
Using Dichotomous Keys Middle School Scientists Curriculum
BioNinja Dichotomous Keys
Cultural and religious importance of plants
Many different cultures and religions have specific uses for particular plants. Certain plants may be used in various holidays or ritual observances.
One of the goals of Social Studies is to expose students to the diversity of ethnic, religious, and cultural observances in our world.
The College, Career, and Civic Life (C3) Framework for Social Studies State Standards notes that students should be able to describe how religions are embedded in culture and cannot only be isolated to the “private” sphere, and identify which religious communities are represented or obscured in public discourse.
Thus, science and social studies teachers can work together to create multi-disciplinary units.
Ethnobotany
The study of a region’s plants and their practical uses through the traditional knowledge of a local culture and people. An ethnobotanist studies local customs involving uses of local flora for many aspects of life, such as plants as medicines, foods, intoxicants and clothing.
Ethnobotany, US Forest Service
Plants in the Jewish tradition
The Sabbath year (shmita; Hebrew: שמיטה, literally “release”), also called the Sabbatical year or Shevi’it (שביעית, literally “seventh”.) This is the seventh year of the seven-year agricultural cycle mandated by the Torah for agriculture by Jewish people living in Israel. During this year the land is left to lie fallow, allowing the soil to regenerate nutrients. With certain exceptions, most agricultural activity is not allowed during this year.
Genesis – Shmitah year covenant, Neohasid.org
What is shmita? My Jewish Learning
Lulav and Etrog, the four species Wikipedia
Trees in Jewish Thought
The Seven Species of plants in the land of Israel.
Plants in the Christian tradition
Trees and plants in the Christian tradition
Trees and religion: Christianity
Plants in the Islamic tradition
Islamic garden
Environmental protection – Islamic shariah
Plants in Buddhist tradition
Ecological significance of plants in Buddhism
Plants in Native American traditions
Native American ethnobotany
Native American Plant Use
Plants in Hinduism
Trees and religion: Hinduism
Plants of religious significance
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Learning Standards
Common Core ELA CCSS.ELA-LITERACY.RST.9-10.3
Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
Next Generation Science Standards
2-LS4-1. Make observations of plants and animals to compare the diversity of life in different habitats.
2-PS1-1. Plan and conduct an investigation to describe and classify different kinds of materials by their observable properties.
MS-LS4-2. Apply scientific ideas to construct an explanation for the anatomical similarities and differences among modern organisms and between modern and fossil organisms to infer evolutionary relationships.
National Science Education Standards, The National Academies Press, 1996
Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.
[Use of dichotomous key is a math skill] – Use Math in all aspects of scientific inquiry: Mathematics is essential to asking and answering questions about the natural world. Mathematics can be used to ask questions; to gather, organize, and present data; and to structure convincing explanations.
Benchmarks for Science Literacy
American Association for the Advancement of Science
Students should begin to extend their attention from external anatomy to internal structures and functions. Patterns of development may be brought in to further illustrate similarities and differences among organisms. Also, they should move from their invented classification systems to those used in modern biology…
A classification system is a framework created by scientists for describing the vast diversity of organisms, indicating the degree of relatedness between organisms, and framing research questions.
SAT Biology Subject Area Test
Evolution and diversity: Origin of life, evidence of evolution, patterns of evolution, natural selection, speciation, classification and diversity of organisms.
Teaching About Evolution and the Nature of Science (National Academy Press)
Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.
Massachusetts Digital Literacy and Computer Science (DLCS) Curriculum Framework
Use of Dichotomous key for identification is an algorithm:
Algorithms [3-5.CT.b]
1. Define an algorithm as a sequence of instructions that can be processed by a computer.
2. Recognize that different solutions exist for the same problem (or sub-problem).
3. Use logical reasoning to predict outcomes of an algorithm.
National Curriculum Standards for Social Studies
3. People, Places, and Environments
The study of people, places, and environments enables us to understand the relationship between human populations and the physical world. Students learn where people and places are located and why they are there. They examine the influence of physical systems, such as climate, weather and seasons, and natural resources, such as land and water, on human populations….
During their studies, learners develop an understanding of spatial perspectives, and examine changes in the relationship between peoples, places and environments….
Immunosenescence (aging of immune system)
Introduction
(In this GIF we see Y-shaped antibodies recognizing and attaching to a pathogen, targeting it for destruction.)
Ed Yong writes, there’s a joke about immunology, which Jessica Metcalf of Princeton recently told me:
An immunologist and a cardiologist are kidnapped. The kidnappers threaten to shoot one of them, but promise to spare whoever has made the greater contribution to humanity. The cardiologist says, “Well, I’ve identified drugs that have saved the lives of millions of people.” Impressed, the kidnappers turn to the immunologist. “What have you done?” they ask. The immunologist says, “The thing is, the immune system is very complicated …” And the cardiologist says, “Just shoot me now.”
Immunology Is Where Intuition Goes to Die, The Atlantic
________________________________
Immunosenescence refers to the gradual deterioration of the immune system brought on by natural age advancement.
The adaptive immune system is affected more than the innate immune system. [1]
It deteriorates
* our capacity to respond to infections
* the development of long-term immune memory, especially by vaccination. [2]
This age-associated immune deficiency is ubiquitous. It is found in both long- and short-living species as a function of their age relative to life expectancy rather than chronological time. [3]
It is considered a major contributory factor to the increased frequency of morbidity and mortality among the elderly.
Immunosenescence is not random. It appears to repeat an evolutionary pattern. Most of the parameters affected by immunosenescence appear to be under genetic control. [4]
It is the result of increasing, lifelong exposures to a variety of antigens such as viruses and bacteria. [5]
{This introduction has been adapted from the Wikipedia article, Immunosenescence}
How it works
New medical techniques to fight against Immunosenescence
COVID-19 poses the greatest threat to older people, but vaccines often don’t work well in this group. Scientists hope drugs that rejuvenate the immune system will help.
The text below has been excerpted from How anti-ageing drugs could boost COVID vaccines in older people, Cassandra Willyard, Nature (news feature) 10/14/2020
Immunosenescence explains why older age groups are so hard-hit by COVID-19 [and why] vaccines, which incite the immune system to fight off invaders, often perform poorly in older people. The best strategy for quelling the pandemic might fail in exactly the group that needs it most.
[With aging] some types of immune cell become depleted: for example, older adults have fewer naive T cells that respond to new invaders, and fewer B cells, which produce antibodies that latch on to invading pathogens and target them for destruction.
[With aging] older people also tend to experience chronic, low-grade inflammation [inflammageing.] This constant buzz of internal activation makes the immune system less responsive to external insults.
With many COVID-19 vaccine candidates currently being tested… researchers say it’s not yet clear how they will fare in older adults.
… If COVID-19 vaccines perform less well in older adults, researchers might be able to find ways to tweak the shot itself to elicit a stronger response. Some influenza vaccines, for instance, include immune-boosting ingredients or higher doses of the viral antigen.
But some scientists say there is a better option. They are developing and testing drugs that could improve how older adults respond to vaccines and might also help them fight viruses more effectively in the first place. Rather than working with the limitations of the ageing immune system, they are planning to rejuvenate it.
… One promising class of anti-ageing drug acts on pathways involved in cell growth. These drugs inhibit a protein known as mTOR. In the laboratory, inhibiting mTOR lengthens lifespan in animals from fruit flies to mice.
….The type 2 diabetes drug metformin also dampens down mTOR’s activity, albeit indirectly. Some studies suggest that people who take metformin are less likely to be hospitalized or die if they contract COVID-19.
…diseases such as diabetes and obesity lead to some of the same immune deficits as occur in older age.
… many anti-ageing pathways seem to be linked, says James Kirkland, who studies cellular ageing and disease at the Mayo Clinic in Rochester, Minnesota.
“That is, if you target one, you tend to affect all the rest,” he says. Many of the immune changes that come with ageing lead to the same result: inflammation. So researchers are looking at drugs that will calm this symptom.
… Another class of drug, called senolytics, helps to purge the body of cells that have stopped dividing but won’t die.
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Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Learning Standards
Next Generation Science Standards (NGSS)
HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
DCI – LS1.A: Structure and Function – Feedback mechanisms maintain a living system’s internal conditions within certain limits and mediate behaviors, allowing it to remain alive and functional even as external conditions change within some range.
Evidence statements: In the model, students describe the relationships between components, including:
* A system’s function and how that relates both to the system’s parts and to the overall function of the organism.
* Students use the model to illustrate how the interaction between systems provides specific functions in multicellular organisms
Massachusetts Comprehensive Health Curriculum Framework
Students will gain the knowledge and skills to select a diet that supports
health and reduces the risk of illness and future chronic diseases. PreK–12 Standard 4
8.1 Describe how the body fights germs and disease naturally and with medicines and
immunization
8.2 Identify the common symptoms of illness and recognize that being responsible for individual health means alerting caretakers to any symptoms of illness.
8.5 Identify ways individuals can reduce risk factors related to communicable and chronic diseases
8.6 Describe the importance of early detection in preventing the progression of disease.
8.7 Explain the need to follow prescribed health care procedures given by parents and health care providers.
8.8 Describe how to demonstrate safe care and concern toward ill and disabled persons in the family, school, and community.
8.13 Explain how the immune system functions to prevent and combat disease
Interdisciplinary Learning Objectives: Disease Prevention and Control
8.a. (Law & Policy. Connects with History & Social Science: Geography and Civics & Government) Analyze the influence of factors (such as social and economic) on the treatment and management of illness.
Benchmarks for Science Literacy, AAAS
The immune system functions to protect against microscopic organisms and foreign substances that enter from outside the body and against some cancer cells that arise within. 6C/H1*
Some allergic reactions are caused by the body’s immune responses to usually harmless environmental substances. Sometimes the immune system may attack some of the body’s own cells. 6E/H1
Some viral diseases, such as AIDS, destroy critical cells of the immune system, leaving the body unable to deal with multiple infection agents and cancerous cells. 6E/H4
Vaccines induce the body to build immunity to a disease without actually causing the disease itself. 6E/M7** (BSL)
Footnotes
1 Pangrazzi L, Weinberger B (2020). “T cells, aging and senescence”. Experimental Gerontology. 134: 110887. doi:10.1016/j.exger.2020.110887. PMID 32092501. S2CID 211237913.
2. Muszkat, M; E. Greenbaum; A. Ben-Yehuda; M. Oster; E. Yeu’l; S. Heimann; R. Levy; G. Friedman; Z. Zakay-Rones (2003). “Local and systemic immune response in nursing-home elderly following intranasal or intramuscular immunization with inactivated influenza vaccine”. Vaccine. 21(11–12): 1180–1186. doi:10.1016/S0264-410X(02)00481-4. PMID 12559796.
3. Ginaldi, L.; M.F. Loreto; M.P. Corsi; M. Modesti; M. de Martinis (2001). “Immunosenescence and infectious diseases”. Microbes and Infection. 3 (10): 851–857. doi:10.1016/S1286-4579(01)01443-5. PMID 11580980.
4. Franceschi, C.; S. Valensin; F. Fagnoni; C. Barbi; M. Bonafe (1999). “Biomarkers of immunosenescence within an evolutionary perspective: the challenge of heterogeneity and the role of antigenic load”. Experimental Gerontology. 34 (8): 911–921. doi:10.1016/S0531-5565(99)00068-6. PMID 10673145. S2CID 32614875.
5. Franceschi, C.; M. Bonafè; S. Valensin (2000). “Human immunosenescence: the prevailing of innate immunity, the failing of clonotypic immunity, and the filling of immunological space”. Vaccine. 18 (16): 1717–1720. doi:10.1016/S0264-410X(99)00513-7. PMID 10689155.
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Sunrise Sunset The science and culture
One of the goals of science education is to see how just a handful of basic laws of nature allow us to understand all phenomenon in our physical universe, from the simplest examples (how objects move) to the most complex (how planets orbit stars)
One of the goals of Social Studies is to expose students to the diversity of ethnic, religious, and cultural observances in our world. The College, Career, and Civic Life (C3) Framework for Social Studies State Standards notes that students should be able to describe how religions are embedded in culture and cannot only be isolated to the “private” sphere, and identify which religious communities are represented or obscured in public discourse.
Science and social studies teachers can work together to create multi-disciplinary units. Here is one on sunset, also known as sundown The daily disappearance of the Sun below the horizon due to Earth’s rotation is something that needs to be understood scientifically, and has ties to major world cultures.
(This section has been adapted from Sunset, Wikipedia)
The time of sunset is defined in astronomy as the moment when the upper limb of the Sun disappears below the horizon.
Near the horizon, atmospheric refraction causes sunlight rays to be distorted to such an extent that geometrically the solar disk is already about one diameter below the horizon when a sunset is observed.
Sunset is distinct from twilight, which is divided into three stages:
civil twilight, begins once the Sun has disappeared below the horizon, and continues until it descends to 6 degrees below the horizon
nautical twilight, between 6 and 12 degrees below the horizon
astronomical twilight, when the Sun is between 12 and 18 degrees below the horizon.
Dusk = very end of astronomical twilight, the darkest moment of twilight just before night.
Night occurs when the Sun reaches 18 degrees below the horizon and no longer illuminates the sky.
image by TWCarlson from Wikimedia.
Refraction: Appearances versus reality
We actually see the Sun a few minutes before it rises and a few minutes after it sets. This is due to the fact that the Earth’s atmosphere refracts the rays of light from the sun.
We learn about refraction of light in our section on geometric optics.
Looking at the situation from the side:
Standing at the beach, looking out towards the horizon, we would see this:
When sun just disappears, the center of the sun is 56’ below. the horizon (almost one degree!). What you see. True position. 34.5’ True position. What you see. 34.5’ 56’ Moment of sunset. Height = 0.
This image from Latitude and Longitude powerpoint by Darleen Cross.
Refraction of light is the reason for mirages – the naturally occurring phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky.
Here’s a spectacular mirage (magnified) that was seen at the Scottish Open golf tournament in Aberdeen, 2014.
Cultural connections
The significance of sunrise and sunset in cultures around the world:
Jewish
In Jewish culture the precise time of sundown and sunrise is of practical and religious importance.
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Observant Jews pray three times daily, and the first prayer service occurs after sunrise, and the last prayer service must occur before the next one.
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Observance of Shabbat, the Jewish Sabbath, is considered to be one of the most important ethical-ritual practices in Judaism. In order to safeguard its observance the timing of sundown should be known as precisely as possible. To avoid any possible violations of Sabbath laws, observance of the Sabbath begins a number of minutes before this time.
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Observance of Jewish festivals, such as Passover, Sukkot, and Shavuot, begin at nightfall. This is why people commonly say that “Jewish holidays begin on the evening of the day before.”
Daybreak עֲלוֹת הַשַּׁחַר alot ha’shachar) – when the first rays of light are visible in the morning
Sunrise הַנֵץ הַחַמָּה, hanetz ha’chamah – when the entire disc of the sun appears over the horizon.
Sunset שְׁקִיעַת הַחַמָּה, shkiyat ha’chamah – when the disc of the sun falls below the horizon
Twilight – bein ha’shemashot בֵּין הַשְּׁמָשׁוֹת, (between the suns) – the period between sunset and nightfall. The status of this time was never clearly delineated in traditional Jewish law. Therefore, on the Sabbath, festivals, and fast days the stringencies of both the previous and following days usually apply.
Muslim
This section is excerpted from a discussion at Islam.stackexchange.com
During the time of the prophet, as was also the case in the Hebrew world and in pre-Islamic Arabia, the day was not calculated as a twenty-four hour period starting at midnight (as our current system of time does). Rather, each day would marked at sunset, and would consist of two parts, starting with “Night” (ليل) and proceeding to “Day” (نهار).
The Qur’an itself does not define “night” clearly; while there are many references associating “day” with the sun and brightness and associating “night” with darkness and concealment, the exact delineation between the two is not so precise.
In fact, according to the classical text الجامع لأحكام القرآن, Imam Qurtubi claims that God alone knows the exact measure of night, based on the revelation in Surat Al-Muzzammil that “Allah determines the night and the day” (الله يقدر الليل والنهار).
According to Lane’s Lexicon, ليل and نهار are opposites, with no intervening period between them. Day, being defined as “the time from the rising of the dawn to sunset”, would thus perfectly complement night, which would by extension be defined as the time from sunset to the rising of the dawn (i.e. sunset to Fajr).
Similarly, Brill’s Encyclopedia of the Qur’an considers the night to include everything from the “evening twilight” (شفق) until “the breaking of morning” (سحر), which immediately precedes the dawn (فلق) itself.
Surat al-Baqarah regulates the nights of fasting until “the white thread of dawn is distinct from the black thread” (يتبين لكم الخيط الأبيض من الخيط الأسود من الفجر), which correlates strongly with the above definitions.
It is important to note that, colloquially, the word ليل (night) can also be overloaded in a similar manner to the English “day”, wherein it can be used to refer to an entire 24-hour period (more accurately, an entire period from sunset to sunset) rather than the night-time in particular. The intended meaning is usually clear in context, especially when ليل is used in a pluralized form, but this too needs to be kept in mind.
While there has been significant scholarly interest in the exact definitions of night and day, especially in regards to the transitory periods of twilight and dawn, much of this research was not conducted until significantly after the death of the prophet himself. As such, any references to “night” in the hadith literature were not necessarily (or likely) using the the term in any scientifically precise manner.
Hindu
(TBA)
Native American
(TBA)
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Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Learning Standards
National Curriculum Standards for Social Studies
3. People, Places, and Environments
The study of people, places, and environments enables us to understand the relationship between human populations and the physical world. Students learn where people and places are located and why they are there. They examine the influence of physical systems, such as climate, weather and seasons, and natural resources, such as land and water, on human populations….
During their studies, learners develop an understanding of spatial perspectives, and examine changes in the relationship between peoples, places and environments….
8. Science, Technology, and Society
Science, and its practical application, technology, have had a major influence on social and cultural change, and on the ways people interact with the world….
There are many questions about the role that science and technology play in our lives and in our cultures. What can we learn from the past about how new technologies result in broader social change, some of which is unanticipated?… How can we preserve fundamental values and beliefs in a world that is rapidly becoming one technology-linked village? How do science and technology affect our sense of self and morality?
College, Career, and Civic Life (C3) Framework for Social Studies State Standards
College, Career, and Civic ready students:
D2.Rel.4.9-12: Describe and analyze examples of how religions are embedded in all aspects of culture and cannot only be isolated to the “private” sphere.
D2.Rel.12.9-12: Identify which religious individuals, communities, and institutions are represented in public discourse, and explain how some are obscured.
Next Generation Science Standards
5-ESS1-2 Earth’s Place in the Universe
5-ESS1-2. Represent data in graphical displays to reveal patterns of daily changes in length and direction of shadows, day and night, and the seasonal appearance of some stars in the night sky.
NGSS Evidence Statements – Observable features of the student performance: Using graphical displays (e.g., bar graphs, pictographs), students organize data pertaining to daily and seasonal changes caused by the Earth’s rotation and orbit around the sun. Students organize data that include:
i. The length and direction of shadows observed several times during one day.
ii. The duration of daylight throughout the year, as determined by sunrise and sunset times.
iii. Presence or absence of selected stars and/or groups of stars that are visible in the night sky at different times of the year.
NSES (National Science Education Standards)
Content Standard D – Earth and Space Science: Earth in the Solar System
Grades 5-8, page 160. Most objects in the solar system are in regular and predictable motion. Those motions explain such phenomena as the day, the year, phases of the moon, and eclipses.
Why numbers exist
By Kenny Barrese
Image from Imaginary Numbers Are Real, Welch Labs
When I posted last week about Babylonian mathematics, and ancient mathematics in general, I really enjoyed writing the post and engaging with the comments.
Consequentially, I asked if anyone had a mathematical topic they wanted me to ramble about and the only suggestion I got was the imaginary numbers. I may talk a little bit about how they work, but I think I will focus more on why they exist in the first place. Why aren’t real numbers “enough”?
I am going to drop a link to my previous post here: (A BRIEF and INFORMAL EXAMINATION of BABYLONIAN ARITHMATIC) I do this mainly because a familiarity with ancient numeral systems might enrich what I talk about here, but is by no means necessary. I also just enjoy discussing math, so sharing that post gives more opportunities for a discussion to grow.
Without further ado, I present:
A BRIEF and INFORMAL EXAMINATION of WHY NUMBERS EXIST
All numbers are invented (discovered or defined if you prefer) for one of two basic reasons: Some numbers came to our attention because they help us answer questions about the world. Other numbers came to our attention because they help us answer questions of a purely mathematical nature.
That’s it. Quite brief and informal! But maybe not entirely satisfying, so let’s continue on in a bit more detail.
The first numbers humanity concerned itself with are the “counting numbers.” As the name suggests, these are the numbers you would use to count something, starting at one, then two, then three, and so on. These are useful for an obvious reason, counting, as the name implies. Mathematicians often call these the “natural numbers,” because they arise so naturally.
The next two types of numbers are both ancient, but younger than the natural numbers. First come fractions, or ratios. These also arise from obvious questions about our world. For example, if you hire five field hands and they harvest a total of seven bushels of grain in a day, how much grain did you get from each worker?
Hopefully your modern mind answers seven-fifths of a bushel (7/5 bushels)! Unfortunately, we are taught decimals before we learn fractions, so you might also be inclined to say 1.4 bushels (that is alright in this case, but imagine we had seven workers who harvested five bushels, wouldn’t 5/7 bushels be a lot nicer than 0.71428571428571428571428571428571 bushels? And even that is not exactly right).
Either way, fractions, what modern mathematicians call the “rational numbers” (from the word ratio) have entered the picture.
The ancient world was just fine with fractions! The Greeks might say each worker harvested a fifth part of seven bushels, representing it as a ratio between 7 and 5. The Egyptians would probably say that each worker harvested one bushel and one third of a bushel and one fifteenth of a bushel, because they expressed (most) every fraction in terms of one over a natural number (and it turns out that 2/5 is 1/3+1/15).
And of course the wily Babylonians would have just expressed it as 1,24 meaning 1 one plus 24 one-sixtieths (because the Babylonians did basically everything we do, just using base 60 and pressed into clay using a stick. The Babylonians are hardcore!).
So, fractions were of no problem to the ancients, a state of affairs that makes modern discomfort with fractions all the more disheartening. However, our next numbers, the irrational numbers, were a different story!
A rational number is any number that can be expressed as the ratio of whole numbers. So an irrational number, as the name implies, is a (real) number that cannot be represented in such a way.
The first example of people realizing that a number was irrational that I know of was in the Pythagorean cult (best remembered by lending their name to the Pythagorean Theorem).
One of its members came up with an argument that demonstrated the square root of 2 could not be represented as a ratio of whole numbers. Since the Pythagorean concept of numbers (and maybe even the Greek concept of numbers) was one of ratios, this was highly disturbing.
Even more disquieting to the Pythagoreans, any time you draw a square the square root of 2 is there, staring you in the face. The ratio of the diagonal of the square to the side of the square (remember, numbers are ratios) is always this quantity square root of 2.
Now something the Greeks definitely do not want to acknowledge exists is plainly there any time they draw a square, a very important geometric object. And the Greeks *loved* geometry! The Pythagoreans promptly supressed the knowledge of these “irrational” numbers so damaging to their basic idea of what a number is.
This is the first example, of many, of push back when a new type of number is introduced. Apocryphally, one member of the Pythagorean cult was thrown from a ship to drown because they revealed the necessity of the existence of irrational numbers outside the cult.
Exactly how much the irrational numbers can be thought to “actually exist” in the real world is an open question. Sure, the square root of 2 lies bare to see in any square, but do perfect squares exist?
Consider the following thought experiment (what am I, a philosopher?):
Imagine you had a monomolecular fiber, made from a single strand of some molecule. Imagine you could make a perfect right triangle from this fiber, 100 copies of your molecule on each non-hypotenuse side. Then you would need 100 times the square root of 2 copies of your molecule on the hypotenuse!
Clearly this is absurd, leaving only two options. The first is that there must be some “stretch” in the fiber (or compression), allowing you to get away with 141 (or 142) copies.
The second option is that reality can never be manipulated in such a way as to obtain an instantiation of a perfect isosceles right triangle.
However, since we often use (perfect) squares as a way of conceptualizing reality, the irrational numbers are introduced to help address real world questions the same as the rational and natural numbers.
Like the irrationals, negative numbers also did not receive wholesale acceptance at first. While the use of negative numbers, or anti-quantities, has a long practice, they are generally adopted by merchants before mathematicians.
Once again, they are introduced to examine a “real world” phenomenon, debts. In fact, well up into the 18th century many prominent European mathematicians distrusted the validity of negative numbers. They are not “natural” in the sense that counting numbers and (positive) fractions are! Look around you and point to something that is negative in quantity. One simply cannot point to a lack of something.
On that note, one also cannot point to an absence of something. I am somewhat remiss in that I have not yet addressed zero. Although zero came into usage as a number after the negative numbers did, it gained widespread acceptance long before they did.
Zero is somewhat singular on this list, being the only type of number to contain only one number. There are many natural numbers, fractions, irrationals, and negatives, but only one zero. I won’t say too much about zero, because it could warrant its own discussion. Not bad for a number that basically means nothing.
With zero, our “real numbers” are complete. What the modern mind thinks of as a number line consists of the natural numbers, the rational numbers, the negative numbers, the irrational numbers, and zero. Incidentally, the number line is a fairly recent development, arising in its modern form in the 17th century. Why not stop there, why continue on to the complex numbers?
If you have taken a math course, you might have noticed mathematicians like solving equations. Some are easy, like x – 7 = 0; in this case our unknown quantity, x, is seven.
With a little more work we can solve 5x – 7 = 0; now our unknown quantity is 7/5 (seven fifths).
Notice that by using only natural numbers, we create an equation that requires a rational number that is not a natural number to solve. (Assuming that subtraction is a “thing.” Historically it is, mathematically it shouldn’t be.)
Continuing in this vein, we can consider x^2 – 2 = 0, an equation where all the known numbers are natural numbers, but now the unknown quantity is the square root of 2.
And at this point I should mention that calling it an unknown *quantity* is a little suspect. Is the square root of 2 a quantity? Can we ever have an amount that is literally and exactly the square root of 2? No matter, while this is a lovely question for mathematical philosophers, a modern mathematician is happy to come up with a symbol for the amount and move on.
Moving on, once again using only natural numbers we can write down the perfectly innocent looking equation x^2 + 1 = 0 (not even subtraction here). This will cause much heartache and distress to mathematicians, because it is easy to demonstrate that no real number solves this equation (the way we have constructed the real numbers).
However, if we allow another number, often denoted by the symbol i, to be the square root of -1, then we are off to the races. This “quantity” i, for truly it is no quantity at all as measured by the real world, is the basis for the imaginary numbers.
Now, let me talk a bit about why they are called the “imaginary numbers.” They are one of the few, unfortunate, entities that I can think of that have retained the name hung upon them by their enemies.
Imagine if we, as a nation, decided to no longer be known as “The United States of America” and, instead, would henceforth be known as “The Great Satan.” Not good press. And this is the ignominy that the “imaginary” numbers have been forced to endure.
When it was first proposed, the value i had many detractors (not that it was called i at the time)! One of their ploys to deride i was to label it “imaginary,” and it seems to have worked.
While in the 17th and 18th century negative and imaginary numbers were viewed with similar suspicion and disdain, negative numbers have come into nearly as much social acceptance as positive numbers, while imaginary numbers still labor under a stigma. Why then do they persist to this day?
One reason is that, mathematically, they are incredibly useful. Not in and of themselves, but as part of what are called the “complex numbers.”
A complex number is any combination of a real number and an imaginary number. For example, 7-4i is a complex number made up of the real number, 7, and the imaginary number, -4i.
All real numbers are complex numbers (with imaginary part 0i) and, similarly, the imaginary numbers are complex numbers (with real part 0). Does this mean 0 is both a real number and an imaginary number? Why, yes! I told you 0 is of singular interest!
The complex numbers have an incredible property, unique to the numbers we have talked about so far. If you write *any* polynomial equation, using whatever complex numbers you want as coefficients, then it will have a solution that is a complex numbers.
As we have seen thus far, even just using the whole numbers as coefficients we have obtained polynomials that require fractions, irrationals, and imaginary numbers to solve.
The amazing thing is that, even if you throw open the doors and allow the coefficients of your polynomial to be anything in the wide world of complex numbers, you cannot come up with a polynomial that cannot be solved using the complex numbers.
This is equivalent to saying that complex polynomials factor completely, an extraordinarily useful property. Mathematicians call this property “algebraic completeness.”
So, this is one reason that the complex numbers persist, they are the first example of an algebraically complete set of numbers we can work with.
Another reason they persist is that their application allows physicists to model electrical systems more fully than they could otherwise. Not being a physicist, nor an electrical engineer, I do not feel up to explaining this fully, but once again, numbers are being used because they are useful for modelling real world phenomenon, just as they have been since antiquity and even prehistory (for the written number pre-dates the written word).
That is what I have to say about the complex numbers for now. We continue to use them because they are useful to us, both in the realm of pure mathematics and in our attempts to systematically represent the world around us through mathematics.
I will wrap up by welcoming any further suggestions for topics that you would be interested in exploring. If you are interested in further consideration of this topic, please feel free to leave me a comment. You might also want to read “Negative Math” by Alberto A. Martinez to learn more about the struggles to accept negative and imaginary numbers.
I considered talking about the transfinite numbers (the numbers, yes plural, that are infinite) but this is already a long post. They too received cold welcome by the mathematical establishment.
To read more about this, I would recommend “The Mystery of the Aleph” by Amir D. Aczel. It reads an an intertwined biography of the transfinite numbers and the sad life of Georg Cantor, the mathematician who brought them into the body of mathematics.
Feel free to join in the discussion on his Facebook post Why numbers exist.
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