Welcome to the Moon
Pictures from the Moon
The Apollo Missions (1)
The Apollo Missions (2)
The Full Moon
Tides
Phases of the Moon
Facts about the Moon
Phases of the Moon
The Moon is the second brightest object in the sky after the
Sun and is one of the most familiar objects to human
beings. However, unlike the Sun, which always appears round, the Moon's shape changes as the nights go by. One
night it will be a full bright disk (a Full Moon) and several nights later, it will be half a disk. Look at it a
few nights later again and it may appear to be the shape of a banana, or a crescent if you want to use its proper
term. Eventually, the Moon will not even be visible before going on to be crescent-shaped again, half full and then
completely full. The image to the left shows what the Moon should look like tonight.
The different shapes of the Moon are known as its phases and each phase has a name. As the Moon is such a familiar and easy-to-observe object, its phases have been studied for centuries. We now know a great deal about the Moon's phases, when they occur and what causes them.
The different shapes of the Moon are known as its phases and each phase has a name. As the Moon is such a familiar and easy-to-observe object, its phases have been studied for centuries. We now know a great deal about the Moon's phases, when they occur and what causes them.
The reason why the Moon goes through phases is because of
its changing position in relation to the
Sun and Earth. Earth is a planet which travels around, or orbits, the
Sun. It takes just over 365 days (a year) for
Earth to
complete one orbit. But, while Earth is orbiting the
Sun, the Moon orbits Earth. It takes the Moon just over 27 days to
complete one orbit of Earth (27.3 days to be precise). As the
Sun is a star, it generates its own light. It is the only
object in the Solar System to produce light. All other objects in the Solar System - the planets and their moons, the
asteroids and comets - reflect light shone on them from the
Sun. This means that only the sides of the objects receiving
light from the Sun will be lit up. It is only possible for half of a round object, like a planet or most larger moons, to be
lit up by the Sun. And this is the simple reason why there is day and night on
Earth. The half of Earth where it is day is the
side that is receiving light from the Sun. The half of
Earth where it is night is the side that isn't receiving light from the
Sun.
Diagram showing how day and night is caused by light from the Sun.
As mentioned above, a New Moon occurs when the Moon is in between Earth and the Sun. Sometimes, when the Moon is new, it is positioned so that it actually blocks the view of the Sun from Earth. The results in an eclipse. By an amazing coincidence, the Moon is 400 times smaller than the Sun, but it is 400 times closer to Earth than the Sun is. This means that, when viewed from Earth, the two objects actually appear to be the same size. This means that when the Moon is exactly in front of the Sun, it completely obscures the Sun's disk and can turn day into night. This event is known as a total solar eclipse. See this page for more information.
It is also sometimes possible for
Earth to block sunlight to the Moon. This happens when
the Moon is in its Full Moon phase. When this happens,
Earth simply casts a shadow on the Moon. It can either be partially or
totally eclipsed. During a total lunar eclipse, the Moon doesn't appear totally dark as light from the
Sun is refracted through Earth's atmosphere which reflects dimly on the Moon and gives it a dull brownish colour as shown in the image below.
