describe to me the sun-earth-moon system?

Answer 1

>> The Sun-Moon-Earth relation

The earth revolves around the sun every 365 days. The Earth is also rotating on its axis, once every 24 hours. This way, each 'side' of the earth is exposed to the Earth's rays, causing day. While the Earth is revolving around the Sun, the Moon is also revolving around the Earth, taking around 27.3 days to make a full revolution.

> Eclipses

Eclipses are formed around 4-7 times per year. There are two types, lunar and solar eclipse. When the Sun-Earth-Moon are in a perfect line [occasional, and in that order shown above], the Earth's shadow falls on the moon. During the full moon in the night, the Earth's shadow will fall on the moon, and the moon will 'disappear', forming lunar eclipse.

When the order is Sun-Moon-Earth, the sun is blocked by the moon. Though the moon is much smaller than the sun, it is much closer to the Earth, making it seem bigger. Solar eclipses, as they are, appear only during new moons, and tend to happen during equinoxes, for its orbit tends to get in the sun's rays.

>> Earth and moon

The phases of the moon can be seen every 29.5 days from Earth. The same side of the moon is visible from Earth because as it rotates, it also revolves around the Earth. All sides of the moon are exposed to the sun however. The moon 'starts' its lunar cycle between the sun and the Earth but not in a line, usually. That is a new moon. The side that is 'lit up' by the sun is facing away from us, so we see no moon. Then, gradually, sides of the moon are visible towards us as it moves counter-clockwise around the sun. In the steps of the lunar cycle: Waxing crescent [more than 1/4 of the lighted], First Quarter [half], Waxing gibbous [more than 3/4 of the lighted], full moon [all of the lighted], and then the amount of lighted surface we see gradually decreases. Waning gibbous [less than 3/4], Third Quarter [Half], and finally the Waning Crescent [less than 1/4], and a new moon once more, after 29.5 days.

The moon's gravitational pull also creates tides on Earth. Every day, every place on earth goes through two high tides and two low tides every day. When it is during the quarter moons of the lunar cycle, neap tides occur. When it is during the new and full moons [either sun and moon are on the same side, or different sides], there are spring tides, which show the largest difference between the high and low tides.

>> Earth and Sun

During the Earth's revolution around the Sun, it goes through 2 equinoxes, and two solstices. Note that the Earth has a tilted axis [at 23.5 degrees]. When the one of the poles are tilted towards the Sun, it is a soltice. These solstices occur during December and June. During December, the northern hemisphere is tilted away from the Sun, experiencing winter. The shortest day is also in the Northern Hemisphere, in the North Pole. During the June solstice, the northern hemisphere is tilted towards the sun, experiencing summer. The longest day is also in the North pole, during that time.

During the equinoxes [when eclipses tend to happen], neither poles are tilted towards the sun, making both hemispheres receive the same amount of energy. Therefore, while the Northern Hemisphere experiences autumn in the Autumnal Equinox [during September 21st], the southern experiences spring. During the Vernal Equinox, during March 21st, it is the Southern Hemisphere's turn to experience spring. The northern hemisphere now experiences autumn..

Good luck =)

Answer 2

The Moon orbits the Earth, which in turn orbits the Sun.

The mutual gravitational attraction between the Earth and the Moon is not the center of gravity of the Earth, even though the Moon "goes around" the Earth. The Earth actually wobbles around a bit as the Moon orbits it - pulling it a bit away from its own center of gravity. If you can picture the hammer toss in the Olympics, then this is very much the same as the Earth-Moon system.

The point around which the Earth and Moon spin is called the baricenter. This point is the common center of gravity between the two bodies. It is this point that actually orbits the Sun along the "Earth's" orbit.

Then you have the same situation between the Earth and the Sun. The earth-moon baricenter causes the Sun to wobble a bit as well as they orbit. There is, therefore, a baricenter between the Sun and the Earth-Moon system's orbits as well.

This phenominon is one of the ways astronomers detect planets orbiting other stars. Current imaging technology is not powerful enough to directly see planets that orbit other stars. In stead, astronomers can measure changes in the light coming from the star and deduce a wobble in the star. That wobble is caused by planets orbiting them. Unfortunatlely, planets as small as Earth don't wobble their stars very much - so this is a bad method to find possible habitable worlds, at least with current technology. Planets found in this way are usually as large as Jupiter, or larger, and they orbit their stars much closer than Jupiter - even as close as Mercury or closer!

Answer 3

From Mars Earth would probably look like a rather large blueish star. The colour of the planet affects how we see it - as Mars is red so it looks red from Earth. As Earth has a rather large moon the star may (but probably not with the naked eye) be seen to slightly change shape. However, unlike Mars the Earth would only really be visible just after sunset and just before sunrise because it's closer to the sun (like Venus and Mercury are on Earth). Because Earth is further away from the sun than Venus and Mercury it would be visible for longer than the other two. Distant constellations and Alpha centauri would look no different. In astronomical terms Mars and Earth are right next to each other. It's like taking one step closer to a distant mountain and expecting it to look larger.

Answer 4

The sun stays still, the Earth orbits the sun, the moon orbits the Earth.