VERNAL EQUINOX Beckons..

There are two equinoxes every year – in March and September. 

The Sun will rise due east and set due west on the equinoxes (on all other days the Sun will rise either north or south of east, and set north or south of west)
The length of day and night are nearly equal (No need for exact maths on this page)

1. SEPT - Autumn Equinox = equal day/night

2. Night increases , Daylight decreases

3. DEC - Winter Solstice = shortest daylight/longest night - northern hemisphere tilts away from sun so least exposure to sun and shorter days.

4. Daylight increases, Night decreases until ..

5. MAR - Spring Equinox = equal Day/night

6. Daylight hours continue increase until..

7. JUNE - Summer Solstice = longest daylight/shortest night - northern hemisphere tilts towards sun so gets max daylight.

8. Daylight decreases until... Goto 1.

Without the earths axis tilt it would be equinox all the time and we would have no Winter or Summer.

Spring equinox 2012 in Northern Hemisphere:
March 20, at 05:14 am

Back to skool for the overall picture: 

....and for those who want to sing-a-long-a-science:

nb. Disclaimer - As with all science if you go into it at a professional level you find the above is so basic that it is almost misleading, but without the above framework it would be practically impossible to really understand the movement of the earth around the sun at a higher level. (-: