Sun, Moon and Earth

Most of the answers lie in the fact that the Moon orbits the Earth and the Earth orbits around the Sun. The Earth also rotates on its own axis, anti-clockwise from west to east, thus giving night and day. The simplest way to understand this and to demonstrate it to a child is by means of a globe, with a light shining on it brightly from one side. By gently rotating the globe anti-clockwise, you will see quite clearly that it is "daytime" on the side nearest the light and "nighttime" on the other side. This will also help to show how it is that there are different time-zones in the world.

The Earth takes a full year, 365¼ days, to complete one revolution of its path around the Sun. The Earth's axis is also tilted, so, at one point in its path, the North Pole is closer to the Sun and the South Pole further away from it. This gives summer in the northern regions and winter in eg Australia. At a later point, when the South Pole is closer to the Sun, the seasons are reversed. During the winter months the Sun is low in the sky. Its rays fall obliquely and must therefore cover a much larger surface area. Consequently, they cannot heat the Earth's surface so much and the weather is therefore colder.

The phases of the Moon
The Moon orbits around the Earth. The time it takes to go from one phase and to return to the same phase again is about 29 days and 12 hours, roughly a month. All the various phases of the Moon seen by us are determined by the position of the Moon in relation to the Earth and Sun.

New Moon
When it is new Moon, the Moon lies between the Earth and the Sun. The side away from us is lit by the Sun but the side close to us is in darkness so the Moon is, therefore, invisible. About two days later a narrow crescent Moon will appear in the western sky: the side of the Moon nearest to us is still mainly in darkness but, as it orbits, the crescent Moon gets a little larger at night.

First quarter
After about seven days in its orbit around the Earth, the Moon reaches a position where it forms an angle of 90° with the Earth and Sun. We can now see the right half of the Moon, lit by the Sun in the southern sky. Through field glasses one can see the outline of the other half of the Moon, though it is not brightly illuminated by the light of the Sun.

Full Moon
Another seven days sees the Moon half-way through its orbit around the Earth. The Sun, Earth and Moon are now in a straight line. That half of the Moon turned towards us is lit up entirely by the Sun. The Moon is now full and will remain visible for the entire night, rising at sunset and setting at sunrise.

Last quarter
From now on the Moon rises later and gets a little smaller each night. Seven days after full Moon, it again reaches a position forming a right angle with the Earth and the Sun, but this time we can see only its left half. The highest position is reached at sunrise in the southern sky. In the following day’s time between Moon-rise and Sunrise will become shorter until the Moon vanishes altogether and the cycle is due to be repeated.

Eclipses of the Sun and Moon
An eclipse of the Sun is only possible in daytime during the period of the new Moon, ie when the Sun, Moon and Earth are in a straight line. It is not the Sun but the Earth which is shadowed, as the Moon hides the Sun from our sight. A total eclipse is caused when the Moon is sufficiently close to the Earth for its shadow to cover the Sun completely. Partial eclipses occur when the Moon is not quite in a straight line with the Earth and Sun but slightly below or above it; if too far from the Earth, the Moon is not able to cover the Sun completely but produces an "annular" eclipse, with the outline of the Sun shining as a ring around the outline of the Moon.

An eclipse of the Moon occurs when it is covered by the shadow of the Earth. This can only occur at the time of the full Moon, when the Sun, Earth and Moon are in a straight line. If the Sun, Earth and Moon were always in a straight line, eclipses would occur each month; this does not happen because the Moon's orbit is not on exactly the same plane as that of the Earth but inclined to it at an angle.