The Earth with its moon, as seen from space.
Click on image for full size
NASA.
The Moon's Orbit and Rotation
The Earth's Moon is the fifth largest in the whole solar system, and
is bigger than the planet Pluto. The Moon has a nearly circular orbit
(
e=0.05) which is tilted about 5° to the
plane of the Earth's orbit. Its average distance from the Earth is
384,400 km. The combination of the Moon's size and its distance from
the Earth causes the Moon to appear the same size in the sky as the
Sun, which is one reason we can have total solar eclipses.
The Moon's orbital period is 27.322 days. Because of this motion, the
Moon appears to move about 13° against the stars each day, or about
half of a degree per hour. If you watch the Moon over the course of
several hours one night, you will notice that its position among the
stars will change by a few degrees. The changing position of the Moon
with respect to the Sun leads to lunar
phases.
Have you ever heard the term the 'far-side' of the Moon? Because of
the effect on the Moon of tidal
forces due to the Earth, the same side of the moon always faces
the Earth. The rotation period and the orbital period of the Moon are
the same. Therefore, Earth-bound observers can never see the
'far-side' of the Moon. Tidal forces cause many of the moons of our
solar system to have this type of orbit.
Shop Windows to the Universe Science Store!
The
Summer 2010 issue of The Earth Scientist, available in our
online store, includes articles on rivers and snow, classroom planetariums, satellites and oceanography, hands-on astronomy, and global warming.
You might also be interested in:
The force of gravity caused by an object gets weaker as you move farther away from that object. In this picture, the Earth is pulling on the Moon, and the Moon is pulling on the Earth. The Moon pulls more
...more
What phase was the Moon in on December, 22 1962? How long does it take the Moon to travel from one phase to the next? Suppose that the Moon spun twice on its axis during each orbit around the Earth. How
...more
Pluto has // Call the moon count function defined in the document head print_moon_count('pluto'); known moons. Charon, the largest by far, was discovered in 1978 by the American astronomer James Christy.
...moreCharon is by far the largest of Pluto's // Call the moon count function defined in the document head print_moon_count('pluto'); known moons. Charon was discovered by the American astronomer James Christy
...more
By 30,000 B.C,. Asian hunter-gatherers had crossed the Bering Strait into North America. These people were the first to inhabit this new land and so they are known as the Native Americans of North America.
...more
"The movements of the heavenly bodies are an admirable thing, well known and manifest to all peoples. There are no people, no matter how barbaric and primitive, that do not raise up their eyes, take note,
...more
The stones of Carnac, France, are probably the most famous stones markings outside of those found at Stonehenge in England. Where Stonehenge is composed of standing stones, the Carnac area has many different
...more
