Our Earth's Satellite, the Moon

Have you ever asked yourself, what is the name of the moon? All the other moons of all the other planets have a name, so what is the Moon's name? Is it Luna? Actually, Luna is the Latin word for Moon. But what is the name of the moon? The Moon. Yep, that's it. The name of the moon is the Moon. Capitalized. Okay, so why is that? Couldn't they think of anything better?


Well, when the Moon was named, it was different. You see, the Moon was the first satellite known to man, so "moon" was not considered a generic name. Think of it this way...we usually call all gelatin "Jello", but it's not all Jello. Jello is just a brand name. What about "Band-aids"? That's also a brand name, since all adhesive bandages are not Band-Aids. Sometimes, a product becomes so popular, that it's name is used to refer to ALL similar products. That's what happened with the Moon. All planetary satellites are called moons, but they are not the Moon!

3753 Cruithne was discovered by telescope on October 10, 1986, by Duncan Waldron and in 1997 it's orbit was determined by Paul Wiegert, Kimmo Innanen, and Seppo Mikkola. It is an asteroid that was captured by the Sun's gravitational pull and is now in orbit around the Sun.
Cruithne is officially 3753 Cruithne, but for ease we will refer it to just Cruithne. Cruithne has been refered to as another moon of Earth, but it doesn't orbit Earth, but orbits the Sun instead. As you can see from the image to the left, Cruithne's revolution around the Sun is so similar to the Earth's that it appears to follow Earth.
If you think they may be in danger of colliding, you have nothing to worry about. Cruithne is many times farther from the Earth than the Moon, and orbits at a different speed. If you look at Cruithne from the Earth's perspective, it would look like a bean shaped orbit, as in the image to the right.

Cruithne is not the only captured asteriod, there have been several other asteroids recently captured by the Sun's gravitational pull which now also orbits the Sun, none of which poses any threat to our Earth.

The tides on Earth are a result of the Moon's gravitational pull. While the Sun also has a gravitational pull, it's strength is less than half that of the Moon. The tides are not caused solely by the Moon's gravity alone, but by the Moon pulling the water towards itself, while the Earth's gravity pulls the tides towards itself.

This constant pulling back and forth helps to create the tides. While the Moon pulls at everything on Earth, the Oceans are especially effected because they are always moving. The Earth experiences higher tides when the Moon and Sun are aligned, these are called Spring Tides, and occur when there is a New Moon and Full Moon. The lower tides occur when the Moon is at it's quarter phases, and is not aligned with the Sun, these are called Neap Tides.

Why does the Moon shine? Why does it sometimes look white and sometimes orange or golden? What is a blue moon?
Lets take these questions one at a time, first: Why does the Moon shine?
The Moon doesn't give off it's own light but reflects the light of the Sun. When the Sunlight hits the surface of the Moon, some of the Moon's material reflects the light back. This reflection is called Albedo, which is expressed in percentage. The Albedo of the Moon is 7%.


For example, ice has a high Albedo because it reflects light back into space, and water has a low Albedo because it absorbs the light.


Earthshine occures when the Earth reflects the sunlight onto the Moon. You only see it when the Moon is in it's quarter phase, and the reflection shows the outline of the whole Moon.

The atmosphere causes the Moon to look orange, gold, or slightly red. When the Moon is near our horizon, the light has to go through more atmosphere than it does when it is overhead. By the time the light reaches your eyes, the blue, purple, and green light has been scattered by molecules, so that only the oranges, reds, and yellows get through. If the Moon looks orange or golden when overhead, that is because of increased pollution in the air at that particular time.
Many times, a large orange Moon is called the Harvest Moon. Many farmers are harvesting their crops and stirring up a lot of dust particles that get into the atmosphere in the Autumn. The Moon is also closer to the Earth at this time of year. These two effects combined give you the large orange, or Harvest Moon.

A Blue Moon is rare. You could say that a Blue Moon happens once upon a Blue Moon.
When there is an extreme amount of dust and smoke in the air, the effect is a Blue moon.

A very large forest fire will cause a Blue Moon effect. When the volcano Krakatoa erupted in 1883, there was a Blue Moon that lasted for 2 years!

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There are hundreds of moons in our solar system, and our Moon is the 5th largest.

The distance from the Earth to the Moon is constantly changing, but according to NASA, the distance from the center of the Earth to the center of the Moon is 238,857 miles (384,403 km).

The Moon has a diameter of 2,159 miles (3,474 km).

The Moon takes 27.3 days to complete one orbit around the Earth, and repeats it's lunar phase every 29.5 days.

It takes 1.225 seconds for light to travel from the Moon to the Earth.

The Moon has a very insignificant atmosphere, so much so that the Moon is usually considered to have no atmosphere, so therefore, there is no "daytime", and no sound. The Sun needs the atmosphere to reflect light back to the Moon's surface, and sound needs air to travel.

The image above right shows the Earth and Moon to scale.

The Moon is tidally locked, meaning the same side of the Moon is always facing the Earth, but we can actually see 59% of the Moon. So how is that possible? It's called libration. The Moon seems to sway, allowing us to see slightly more than the 50% we would see if this didn't happen. Of course, we don't see 59% at once, we see different parts of the Moon at different times, adding up to 59%.

So why does the Moon do this? The moon isn't physically swaying as much as it looks, it just seems to, because of the view we have of it from Earth. The position of the Moon on it's axis, combined with it's rotation, and then the angle from which we see the Moon from Earth, causes it to look like it's swaying. The Moon does actually sway a bit, but never more than 0.04 degrees, this is called Physical Libration.

The dark spots seen on the moon are called Mare, which means "sea" in Latin, because that's what astronomers used to think they were. Maria is the plural form, and I don't mean a girl with a split personality. I mean the lunar maria, which is pronounced differently, you put the emphasis or stress on the first syllable for Mar/i/a and Mar/e.



The lunar maria cover about 16% of the Moon, and most of this coverage is on our side. Nearly 36% of the near side of the Moon is covered by maria. The lunar maria are pools of basaltic lava that flowed into depressions caused by meteors, comets, or asteroids striking the Moon. These solidified lava depressions do not reflect the Sun as much as the Terrae, which are more commonly called the Highlands (and you thought only Scotland had the Highlands). While the mare are associated with an impact basin, Oceanus Procellarum (Ocean of Storms) is an exception. This extremely large area of lunar mare doesn't cover a well defined basin like the other maria of the Moon.

Our Moon is literally covered with impact craters, with more than 500,000 of them close to a mile in diameter, or larger. The Moon has been bombarded with so many celestial bodies that it has what is believed to be the second largest crater in the solar system, the South Pole-Aitken basin which is on the far side of the Moon. This basin is seen as the dark spot in the image to the right. Notice how little mare there is on the far side of the Moon as compared to the near side we see at night?


If you want loads of real time information on our own Moon, you've got to try this Lunarphase software. It's really cool if you are totally into the Moon.

You may have heard of Google Maps and Google Earth, but have you heard of Google Moon?

Check out Google Moon and get a map of the Moon, Lunar landmarks, and information about the six Apollo missions. This is a great site!

Our Astounding Universe
The Major Moons of Jupiter
The Planet Saturn
The Rings of Saturn
The Major Moons of Saturn
The Major Moons of Neptune
The Major moons of Uranus
The Planet Mercury