1. The Earth’s Revolution

2. Revolution – the movement of the Earth around the sun
Rotation is one type of motion that the Earth goes through. Another is revolution
Revolution – the movement of the Earth around the sun

3. Evidence of Revolution

4. One piece of evidence that the earth revolves is the position of the constellations
Constellations that are visible in the winter sky are in different positions in the summer or not visible at all.

5. If the Earth didn’t orbit the sun, no shift would occur
Another piece of evidence for revolution is parallax – the apparent shift in position of stars
If the Earth didn’t orbit the sun, no shift would occur

6. The Earth revolves in the same direction as it rotates, counterclockwise as viewed from the North Pole
The Earth’s orbit is an ellipse or elongated circle. Because of this the distance between the Earth and the sun changes throughout the year

7. Aphelion -- the point on its orbit when the Earth is farthest
Aphelion -- the point on its orbit when the Earth is farthest from the sun
Perihelion -- the point on its orbit when the Earth is closest to the sun

8. The Earth makes one revolution every 365.24 days (one year)

9. Effects of Revolution and Tilt

10. At almost any given time, one hemisphere is tilted toward the sun
Effects of the Earth’s revolution and tilt include seasons and variations in night and day
At almost any given time, one hemisphere is tilted toward the sun

11. This tilting is what gives us the four seasons of the year - spring, summer, autumn (fall) and winter.
Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter and also because the days are much longer than the nights during the summer.

12. Sometimes the northern half of the Earth is pointing towards the Sun, and sometimes it is pointing away. These points in the Earth's orbit are called solstices.
The summer solstice (around June 21st) marks the point at which the north pole of the Earth is tilted at its maximum towards the Sun
The first day of winter (around December 21) for the northern hemisphere is called the winter solstice.

13. On the first day of summer (June 21), the daylight period is the longest of the year.
On the first day of winter (December 21), the daylight period is the shortest

14. There are also 2 days each year, midway between the solstices when neither hemisphere tilts towards the sun
These days are known as equinoxes – daylight and nighttime have equal length

15. The vernal equinox occurs on March 21 marking the first day of spring
The autumnal equinox (September 22) marks the first day of fall