1. Part 1: The Earth – Moon System
Astronomy
Part 1: The Earth – Moon System

2. Earth Motions…Two Types
Rotation: spinning around an axis
Revolution: the motion of a planet around a point in space

3. Earth’s Rotation Thanks to rotation we have day & night
We measure the Earth’s rotation around its axis from one noon to the next noon
This is about 24 hours
This is called a solar day

4. Earth’s Revolution
The Earth revolves around the sun in an elliptical orbit
Earth is about 150 million km from the sun (93 mill miles)
Perihelion: Earth’s closest approach to the sun
Aphelion: Earth at its greatest distance to the sun
Speed: kilometers (km) per hour or 66, mph

5. Earth’s Seasons The Earth is tilted 23.5 degrees
This tilt causes our seasons
So we get…
Spring equinox (March 20 or 21)
Autumn equinox (Sept. 22 or 23)
Summer Solstice (June 21 or 22)
Winter Solstice (Dec. 21 or 22)

6. Vernal Equinox – 21 March arctic circle tropic of Cancer equator
sunlight
tropic of
Cancer
equator
tropic of
Capricorn
sunlight
antarctic
circle

7. Autumnal Equinox – 21 September
arctic
circle
sunlight
tropic of
Cancer
equator
tropic of
Capricorn
sunlight
antarctic
circle

8. Summer Solstice – 21 June tropic of Cancer arctic circle equator
sunlight
equator
antarctic
circle
sunlight

9. Winter Solstice – 21 December
tropic of
Cancer
arctic
circle
sunlight
equator
sunlight
antarctic
circle
tropic of
Capricorn

10. Earth-Sun Motion
The Earth & the sun are revolving around the Milky Way Galaxy at 250 km/s or around 560,000 mph

11. Earth-Sun Motion
And our Galaxy is approaching, and will collide, with the Andromeda Galaxy

12. The Earth - Moon We have one satellite…the moon
It is about 384,000 km or 239,000 miles from Earth
Perigee is the closest approach
Apogee is the furthest

13. Phases of the Moon

14. Half of the Moon is always lit up by the sun
Half of the Moon is always lit up by the sun. As the Moon orbits the Earth, we see different parts of the lighted area.

15. The Moon passes through four major shapes during a cycle that repeats itself every 29.5 days. The phases always follow one another in the same order: New moon First quarter Full moon Third quarter

16. New Moon… The lighted side of the moon faces away from the Earth.
This means that the sun, Earth, and moon are almost in a straight line, with the moon in between the sun and the Earth. 

17. First Quarter Moon
The right half of the Moon appears lighted and the left side of the Moon appears dark

18. Full Moon The lighted side of the moon faces the Earth and the Sun
The Earth, Sun, and moon are almost in a straight line, with the Earth in the middle
Photo by Robin Afinowich

19. Third Quarter Moon Also called a last quarter moon.
Only the left side of the moon appears lighted
The next main phase will be a new moon again

20. Other Phases
There are other phases that fall between the ones we already looked at
Like…
Waxing cresent
Waxing gibbous
Waning gibbous
Waning cresent