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. (-:

The rising and setting Sun.

The Sun rises in the East and sets in the West, yes?...NO.  It only does this at two points in our year.

Equinox - sun rises due east and sets due west.  

These are around 21 MAR and 21 SEP in the Northern Hemisphere - they are the days of equal day and night hours.  In between it gets darker and lighter as the tilted earth moves one cycle around the sun. If the earth did not tilt we would not have Seasons.

Winter solstice - Shortest Daylight hours at midwinter around 21 DEC....There is a  low arc as we tilt away from sun in northern hemisphere - sun rises nearer south east and sets nearer south west - ie it arcs over the south - at midday the sun will indicate which way is south.

Summer solstice - Midsummer is around 21 JUN . There is a higher arc so sun seems higher overhead at midday - rises nearer north east, sets nearer north west.