Moon

Retrograde motion of Mars, June to November, 2003

Who is this guy?Use SkyGazer or StarCal to find out!

The Moon

The moon revolves around the earth with a period of about 29 ½ days ~ one month!

Facts about the Moon…• We see the moon changes its

appearances and position in the sky with approximately 30-day cycle.

• Unlike the stars, Moon can also be seen during the day.

• We also see that the Moon is always involved in eclipses, and

• Its position seems to be well correlated with the tide of the ocean.

• Understanding the motion of the Moon with respect to the Sun and the Earth will explain these phenomena.

Motions of the Sun-Moon-Earth System1. Earth orbits the Sun every 365 ¼ days2. Moon orbits Earth every 29 ½ days

Click on the image to start animation: This is what the orbit of the Moon looks like…

3. The orbit of the Moon around Earth is tilted about 18.5 degrees with repect to the ecliptic plane

4. Moon’s orbit around Earth precesses with a period of 18.5 years

Click on the image to start animation

• The changing phase of the Moon…

• The un-changing face of the Moon…

• Eclipses– Lunar Eclipse– Solar Eclipse

The Face and Phases of the Moon

• The phase (how much and which side of the Moon is illuminated) of the Moon changes with about one month period…

• The face (the features on the surface of the Moon) does not change at all…

The Phase of the Moon

The phase of the Moon depends on the relative position between the Sun, the Earth, and the Moon…

Phases of the Moon

Click on the image to start animation

Moon Rise/Set by Phase

Click on the image to start animation

Why do we Always See the Same Side of the Moon?

The rotation period of the Moon with respect to the universe is exactly the same as the rotation period of the Moon around the Earth.

Is this a coincidence? No! Tidal Lock, Chapter 5.

Seasons, moon, eclipses, tides

• http://qldscienceteachers.tripod.com/junior/astro/tides_etc.html