The Deep Sky

I put last night to good use.

Late in the evening, I found that I couldn’t sleep. About midnight, I looked out of the window, and I saw that the sky was incredibly still and clear. So, why not? I put on my boots, my hat, my scarf and the gloves and I walked out to the park at the top of the hill.

The Moon was up and the park was covered in snow. It was bluish-silver in the moonlight. It was completely still. And the sky was amazing – a proper ‘deep sky’, the sort you don’t normally see from the middle of a town.

I looked at the Plough, and located Mizar. (Mizar is the star where the ‘handle’ of the Plough bends.) And to my great surprise, I was startled to pick out Alcor next to it! Alcor is (possibly) a companion to Mizar*, and it’s a test of seeing coditions as it’s a fifth-magnitude star. Being able to see it from the middle of a town, on a Moonlit night, is pretty downright odd. And yet, there it was. You do not expect to be able to see things fainter than +4 mag inside a large town!

I can only account for it by two things. One was the incredible stillness of the air – there was no wind and it was cold. The stars were barely flickering at all. The only other places I’ve seen them that still were up at the summit on La Palma and on Mauna Kea. (You kind of expect them to look more still when you’re above more than half the mass of the atmosphere! You don’t expect them to look still from near sea-level. In England. In Stevenage. Thirty miles from London.)

The other thing was the day’s rain and then snow. I guess all the precipitation had washed most of the usual pollutants out of the air. (Certainly it seems fresher at the moment then it usually does here.) And the combination of the two led to quite a spectacular night sky.
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*There’s debate on this. The separation is rather large – about a parsec or so. On the other hand, Mizar and Alcor are a common proper motion pair, which would tend to argue in favour of some sort of link. So there’s debate. There’s always debate…

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