1. Guided Notes on the Sun-Moon-Earth System
Chapter 28, Section 3

2. Every society, from ancient times to the present, has based its calendar and its timekeeping system on the apparent motions of the Sun and Moon.

3. 2. The Sun rises in the east and sets in the west, as do the Moon, planets and stars. These daily motions result from the Earth’s rotation.

4. 3. Annual changes in the length of the day and the average daily temperature are the result of Earth’s orbital motion about the Sun.

5. 4. The plane in which Earth orbits is called the ecliptic
4. The plane in which Earth orbits is called the ecliptic. Earth’s axis is tilted relative to the ecliptic at about 23.5˚. As the Earth orbits the Sun, the orientation of the axis remains fixed in space. At one point, the northern hemisphere is tilted toward the Sun, while six months later, it is tipped away from the Sun. Our seasons are created by this tilt and by Earth’s orbital motion around the Sun.

6. 5. On the day of the summer solstice, the Sun is directly overhead at the Tropic of Cancer, which is 23.5% North latitude. This occurs each year around June 21st, and is the day when the number of daylight hours for the northern hemisphere is at its maximum. Daylight is at a minimum for the Southern hemisphere.

7. 6. On the day of the winter solstice, the Sun is directly overhead at the Tropic of Capricorn, which is 23.5% South latitude. This occurs each year around December 21st, and is the day when the number of daylight hours for the northern hemisphere is at its minimum. Daylight is at a maximum for the Southern hemisphere.

8. 7. The lengths of day and night are equal for both the northern and southern hemispheres on the autumnal equinox and the vernal equinox.

9. 8. A solar eclipse occurs when the Moon passes directly between the Sun and Earth and blocks our view of the Sun.

10. 9. A total solar eclipse occurs when the Moon perfectly blocks the sun’s disk, and we see only the dim, outer gaseous layers of the Sun.

11. 10.Total solar eclipses are only visible from a very small portion of the Earth, while partial eclipses are visible from a much larger portion.

12. 11.Only when the Moon crosses the ecliptic is it possible for the proper alignment for a solar eclipse to occur. When the intersection of the Moon and the ecliptic is in line with the Sun and the Earth, a total solar eclipse can be seen.

13. 12.The Moon’s distance from the Earth increases and decreases as the Moon moves in its elliptical orbit around Earth. The closest point in the Moon’s orbit is called the perigee and the farthest point is the apogee.

14. 13.A lunar eclipse occurs when the Moon passes through the Earth’s shadow. This can only happen during a full moon, when the moon is in the opposite direction from the Sun.

15. 14. Solar and lunar eclipses occur in almost equal numbers
14.Solar and lunar eclipses occur in almost equal numbers. The maximum number of eclipses that can be seen in one year is seven. The last time that this happened was in 1982, and it will not occur again until 2038.