1. Astronomy Unit 4, Section 2
Lunar Orbit

2. Natural Satellites Our Moon The Orbit of the Moon
Vocab Words for “The Orbit of the Moon”
1st Quarter
3rd Quarter
New Moon
Full Moon
Waxing
Waning
Synchronous Orbit
Near Side
Far Side
Lunar Eclipse
Solar Eclipse

3. Natural Satellites The Orbit of the Moon
The moon revolves around the earth every 29.5 days.
The moon rotates around itself every 29.5 days as well!
This means the moon’s orbit is synchronous
A Synchronous Orbit is when the period of revolution is equal to the period of rotation. The moon rotates at the same exact pace that is revolves at!

4. Natural Satellites The Orbit of the Moon
The Synchronous orbit of the Moon causes the moon to have a Near Side and a Far Side.
The Near Side of the Moon is the side of the moon that ALWAYS faces the earth.
The Far Side of the Moon is the side of the moon that NEVER faces the earth.
In 1959 the Russian Mission, Luna 3 (an unmanned space probe) photographed it. This is the first time people saw pictures of the Far Side.
It wasn’t until 1968 that people saw it first hand. Apollo 8 was able to orbit the moon and view the far side. Astronauts Frank Borman, Jim Lovell and William Anders were able to see it.

5. Near Side on the Left and Far Side on the Right
Natural Satellites
Near Side on the Left and Far Side on the Right

6. Natural Satellites
Note the differences between the Near Side and Far Side
This is why scientists believe the Earth has had some impact on the Formation of the Moon.

7. Natural Satellites The Orbit of the Moon
As the moon revolves around the earth it looks different in the sky each night.
The different appearances of the moon in the night sky are called the Moon Phases.
The moon is ALWAYS 50% lit up from the sun.
It isn’t always the lit up side that is facing the earth.
What we see at night (the different phases) are combination of the lit up portion of the moon and side of the moon facing the earth.

8. Natural Satellites

9. Natural Satellites
The Moon goes through 8 distinct phases during each of its revolutions.
New Moon
Waxing Crescent
1st Quarter
Waxing Gibbous
Full Moon
Waning Gibbous
3rd Quarter
Waning Crescent

10. Natural Satellites

11. Natural Satellites
New Moon is when none of the lit up portion of the moon is facing the earth.
The moon appears completely dark in the night sky from earth.
Full Moon is when all of the lit portion of the moon is facing the earth.
The moon appears completely bright in the night sky from earth.

12. Natural Satellites
The Waxing phases are the growing phases of the moon.
When the moon goes from new moon to full moon
The Waning phases are the shrinking phases of the moon.
When the moon goes from full moon back down to new moon

13. Natural Satellites The Orbit of the Moon
The moon’s orbit is tilted 5 degrees to the earth’s orbit.

14. Natural Satellites The Orbit of the Moon
This tilted orbit means that solar eclipses and lunar eclipses will NOT occur each month.
A Solar Eclipse is when the moon comes right in between the earth and sun and casts its shadow upon the Earth.
The Moon should be New Moon phase at this point.
A Lunar Eclipse is when Earth falls directly in between the sun and the moon and casts its shadow upon the moon.
The Moon should be in Full Moon phase at this point.

15. Natural Satellites Solar Eclipse Position of Sun, Moon & Earth
View from Earth
Total Solar Eclipse

16. Natural Satellites Lunar Eclipse View from Earth
Total Lunar Eclipse
Position of Sun, Moon & Earth