Wednesday, 22 July 2009

Eclipsed

photo of 1999 eclipse (reproduced with kind permission from Luc Viatour)


This morning across Asia something rare and spectacular decorated Earth for, in some places, six minutes and 39 seconds.

Day-time darkness.

The 22 July 2009 total eclipse of the sun was the longest of this century; there won't be another that will cast that eerie silent night-time feel (I was a mere teenager during the 1999 South West (of England) astronomical display but I remember it well: dogs barking, birds sleeping, crowds oohing, me shivering) for so long until 2132. The solar eclipse - all to do with the burning sun. Ah, not so.

Let us not forget the moon in this affair.

A solar eclipse can only happen at new moon - when the moon is positioned between the sun and Earth. At new moon we usually don't see the moon. Firstly, because the side of the sphere we cannot see is lit, and also because the sun and moon rise together, thus we'd be looking at the sun. And that would hurt. Usually, the sun, moon and Earth don't align perfectly; there's a slight degree of discrepancy. But when they do line up at new moon, we get a solar eclipse.

But why is this one so talked about?

In eclipse parlance, this was a biggie. And there are a couple of reasons why. On 22 July 2009, the moon's new-moon phase was in perigee: closest to Earth during its egg-shaped cycle. About 222,000 miles away from your window. Earth, on the other hand, was almost at its furthest from the sun (aphelion*). Combine these and the moon appears 8% larger than the sun. So pass a big moon in front of a smaller sun and it takes quite a long time for the Earth to reappear from the moon's shadow. The centre of the darkness, in the umbral shadow, stays darker longer (than the penumbral).

In August, we have a penumbral lunar eclipse in the northern hemisphere across Europe and Africa. If you're lucky, you may see a slight dimming of the moon's surface during full moon. But I'll talk about this a little nearer the time.

So remember - don't just praise the sun for a solar eclipse; the moon plays an enormous part.

Great picture of 2009 total solar eclipse that I dare not reproduce here.


*for fellow language geeks, note perihelion/perigee (closet to: sun/Earth) and aphelion/apogee (furthest from: sun/Earth). From the Greek: prefix peri meaning "near"; prefix apo meaning "away". Combine with helion for the sun and gee/gea for earth. Very nice.

2 comments:

Maia said...

Lovely article thank you Rob
Blessed Be
Maia

Rob Self-Pierson said...

Thank you as always, Maia