A month is about as long as a natural cycle of the Moon. The word month comes from the word Moon. Not all months are the same length.

Here is one way of helping to remember them:
Thirty days hath September, April, June, and November. All the rest have 31, Except for February all alone, It has 28 each year,' but 29 each leap year.

Here are the months and their lengths:

1 January 31 days
2 February 28 days, 29 in leap years
3 March 31 days
4 April 30 days
5 May 31 days
6 June 30 days
7 July 31 days
8 August 31 days
9 September 30 days
10 October 31 days
11 November 30 days
12 December 31 days
In parts of the world away from the Equator, the months are marked by the height of the midday Sun. The Sun is at its highest on June 21st (called the Summer Solstice) and at its lowest on December 21st (called the Winter Solstice. The points half way between these are the Autumn Equinox (which means equal day and night) at September 21st, and the Spring Equinox on Marsh 21st. In many places the months are marked out by significant changes in the weather. You can find out about these monthly changes in the books below.