Clear skies to you!

One of the joyous portents of coming summer in my bit of the northern hemisphere, is the arrival of the Orion constellation rising high in the night sky - invisible during the winter months.

It is home to the famous 'Horse Head' nebula, but you need a 50 foot telescope perched on the top of a mountain in Hawaii to see it, nestling amongst that little red blob on the belt.

It is Her Indoors' favorite star formation and, over the years, it has become mine too. It has such a pleasing shape and it looks like an old friend - an exclusively summer friendship. When we went to Cuba a few years ago, we arrived at night and looked up into the sky over Havana to see Orion waiting for us, but this time he was lying on his side.

There are certain constellations that only those living in the southern hemisphere will see, like the Southern Cross. I expect they have similar connotations for the people that live under them, like travelers in the Antarctic. One of the few drawbacks of living in our compact but adorable city apartment is the light pollution from all the cadmium lamps, but Orion is strong enough to cut through them on a clear night. When you compare satellite pictures of Havana and London, you realise just what a problem this can be. The title of this post is the traditional greeting or sign-off amongst amateur astronomers.

There is an astronomical, photographic technique which enables amateur photographers to pick out nebulous details without using long exposure and all the attendant problems - like the satellite trails that you can see in the picture above - and it was developed by a man in the USA, using nothing but a simple video camera, telescope and $20 worth of old computor.

One day, he trained his telescope (using a cheap tracking device) on a patch of clear sky in bright sunshine, through which he knew the space shuttle was passing. He fed the images through his computor which he had programmed to select split-second samples during which the air-turbulence had come to a standstill for a millisecond or so as it changed direction in the desert heat. These images were then 'stacked' one over the other, layer upon layer, until he had a crystal-clear, digital picture of the shuttle on which you could clearly read the logo, 'NASA'.

He telephoned NASA to ask why they had the loading-bay doors open when it passed overhead that day, and there was a stunned silence on the other end of the line. A day later, two NASA officials turned up on his doorstep to demand to know how he had obtained that information, and he showed them his images.

You can now buy that simple software for astro-photography when you buy a cheap little telescope, and it has changed the nature of terrestrial observation forever. It probably changed espionage and defence too!