Why phases of the moon happen

Our Moon's day and night cycles are a little longer than Earth's — the Moon spins on its axis once every Our Moon's period of rotation matches the time of revolution around Earth. In other words, it takes our Moon the same length of time to turn once on its axis as it takes it to go once completely around the Earth!

Do other planets have moons? Several of the planets in our solar system have natural satellites that orbit them. Some are so recently discovered that they have not yet been named. Mars has Phobos and Deimos, two small moons that circle very close to the martian surface.

Jupiter has more known satellites than any other planet — 61! Saturn has at least 31 satellites, Uranus has 27, and Neptune has 13 — and more are being discovered all the time! Pluto has one moon — Charon — the largest moon with respect to the size of the planet it revolves around. Only Mercury and Venus do not have any known satellites. Satellites are not restricted to planets; tiny Dactyl was discovered orbiting the asteroid Ida in ! LPI Education. Why does our Moon's shape change? Nearside view of Earth's Moon as seen by the Galileo Spacecraft.

Farside view of Earth's Moon as seen. False color view of Saturn's moon Epimetheus. Jupiter's moon Europa. If we could magically look down on our solar system, we would see that the half of the Moon facing the Sun is always lit.

But the lit side does not always face the Earth! As the Moon circles the Earth, the amount of the lit side we see changes. These changes are known as the phases of the Moon and it repeats in a certain way over and over.

At new moon, the Moon is lined up between the Earth and the Sun. We see the side of the Moon that is not being lit by the Sun in other words, we see no Moon at all, because the brightness of the Sun outshines the dim Moon!

When the Moon is exactly lined up with the Sun as viewed from Earth , we experience an eclipse. As the Moon moves eastward away from the Sun in the sky, we see a bit more of the sunlit side of the Moon each night. A few days after new moon, we see a thin crescent in the western evening sky.

The crescent Moon waxes, or appears to grow fatter, each night. When half of the Moon's disc is illuminated, we call it the first quarter moon. This name comes from the fact that the Moon is now one-quarter of the way through the lunar month. From Earth, we are now looking at the sunlit side of the Moon from off to the side.

The Moon continues to wax. Once more than half of the disc is illuminated, it has a shape we call gibbous. The gibbous moon appears to grow fatter each night until we see the full sunlit face of the Moon. We call this phase the full moon. As a result, we can see the whole of the lit side of the moon. At new moon, exactly the opposite alignment exists, with the moon being between the Earth and the sun.

At that point, we can only observe the shadowed side of the moon. At first and third quarter moons, the moon is at a 90 degree angle from the Earth and sun. We can see half of the lit side and half of the shadowed side. The crescent and gibbous periods are observed as the moon transitions between these points in its orbit.

There are four terms used to describe the "in between" moon phases: waxing, waning, crescent and gibbous. Waxing is when the moon's lit area appears to be increasing, whereas waning is when the lit area appears to be decreasing.

Crescent is when the moon appears less than half illuminated, and gibbous describes when the moon appears more than half illuminated. An eclipse occurs at full moon phase when the Earth casts a shadow on the moon, temporarily making it go fully or partially dark.

Partial eclipses occur several times per year, whereas a total eclipse occurs very infrequently. Eclipses are relatively short events, and you can observe over the course of a few hours the moon going from full to dark and back to full again.

Christopher Williams has spent over 11 years working in the information technology, health care and outdoor recreation fields. He has over seven years of technical and educational writing experience, and has brought strong skills and passion to the Demand Studios team in articles for eHow and Trails in Related Articles Dark Moon Vs. New Moon.