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# Earth-Sun motion and seasons

### Six months later, in December, when Earth has moved to the opposite side of its orbit, the axis points  23.5 degrees away from the sun. This is the winter solstice, the first day of winter.

On days between these extremes, Earth’s axis is leaning at amounts less than 23.5 degrees to the rays of the sun.

### “Our first day of winter (December 21), it is the first day of summer for places like South Africa, Australia, and Argentina. This is because when the northern hemisphere is tilted away from the sun, the southern hemisphere is tilted toward the light and vice versa. Whichever pole is tilted toward the sun experiences summer on that solstice, and the other hemisphere experiences winter.”

• Mr. Gruszka’s Earth Science GIFtionary

Tarbuck Lutgens

## Learning Standards

### Massachusetts

8.MS-ESS1-1b. Develop and use a model of the Earth-Sun system to explain the cyclical pattern of seasons, which includes Earth’s tilt and differential intensity of sunlight on
different areas of Earth across the year.

### College Board

ESM-PE.2.5.2 Construct a representation of Earth’s orbital path and rotation, and identify the length of time each takes. Identify key positions (solstices and equinoxes; perihelion and aphelion) of Earth throughout its orbit, and link these positions to seasonal changes.

### Benchmarks for Science Education, American Association for the Advancement of Science

Because the earth turns daily on an axis that is tilted relative to the plane of the earth’s yearly orbit around the sun, sunlight falls more intensely on different parts of the earth during the year. The difference in intensity of sunlight and the resulting warming of the earth’s surface produces the seasonal variations in temperature. 4B/H3** (BSL)