Spring Equinox

Today is the first day of Spring in the Northern hemisphere. It is defined as the time when, in the first half of the year, the tilt of the Earth's axis is neither inclined away from nor towards the Sun. But it means more than that. Winter is, hopefully, over. Days and nights are the closets to being roughly of equal length and historically many cultures celebrate the end of darkness and the re-birth of light and life. In Egypt the day has been celebrated as far back as 2700 BC. The ancient Persians celebrated it as the day when Jamshid, the mythical king, ascended to the throne. Indeed it is still observed by many people in Iran to this date. In Japan it is an official national holiday, and time is spent visiting family graves and holding family reunions. The Jewish feast of passover falls on the first full moon after the spring equinox. Easter is also calculated by reference to the spring equinox. Many cultures, from the Vikings in Europe to the Tamils in South Asia recognise it as a special day, one to be celebrated.

Interestingly, equinox happen on other planets. Any planet that has a significant tilt to its rotational axis experiences an equinox. The most dramatic of these is on Saturn, where the equinox places the normally majestic ring system edge-on facing the Sun. As a result, they are visible only as a thin line when seen from Earth. Also, they pick up very little light from the sun and shine themselves by planet-shine only. This happens approximately every fourteen years, the last being in August 2009. Since then its ring system has been slowly 'opening up', making for good viewing.

For modern day astronomers it represents not only an astronomical landmark, it often heralds the return of the spring and summer constellations. Familiar friends begin to return to the night sky, however short they are. For many others as well today represents a significant event. The days are getting longer, the sun is getting warmer, the garden is starting to fill out with new life. Enjoy, for summer is on its way.