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Village Sky At Night with Brian Watkiss

Not so dim, after all

Posted on September 24 2011 at 11:16:31 0 comments

Amateur astronomer Brian Watkiss peers into the Village night sky.

I’ve had a few queries lately about items seen in the general press so I’d like to take this opportunity to answer them. Firstly, comet Garradd is still visible but you will need binoculars to see it. It is in a really good location for us at the moment – in the sky, yes – but in the middle of the south western sky.

Looking overhead as soon as it gets dark, Vega is easily visible, together with Deneb to its left and Altair below, the three forming the Summer triangle. Over to the right, a dimmer star forms an equilateral triangle with Vega and Altair and Garradd will drift slowly past this during the month, starting a little to the left and below.

Another comet, Elenin, would have been visible for a short period in the morning just before sunrise but it appears not to have survived going around the Sun, having broken up and “melted” as it got near.

It would have got as close as about 22 million miles to the Earth, giving rise to stories of global destruction but now we may never know – although the Moon is much closer than that and it just makes the sea go up and down a bit!

Finally, there has been a supernova near the Big Dipper. This has caused excitement because it is relatively close, in a galaxy 23 million light years away. This means, of course, that it actually happened 23 million years ago but it has taken that long for me to write about it.

Unfortunately, its brightness is the problem. If I can take you back to Vega for a moment, it is just about the brightest star in our sky at the moment, yet it has a brightness of – zero! What? You see, when men first started looking up at the night sky, the very first stars they could see after sunset were allocated a brightness (or magnitude) of one. The next ones to “come out” were a brightness of two and so on.

Many years later, when telescopes allowed more scientific studies, the system was tidied up and formalised and the brightest stars were given a magnitude of zero. If you look up at Cygnus, fairly high in the south, the brightest star, Deneb, has a magnitude of about 1.

In the middle of the cross is Sadr, with a magnitude of about 2 and at the very bottom is Albireo with a brightness of 3. In between these two is a little unnamed star with a brightness of 4, so Cygnus was obviously engineered to demonstrate the system.

If you now turn and look over to the east, you will see something even brighter that spoils things a bit. It is the planet Jupiter and much brighter than anything else (if the Moon isn’t around). To cope with this, the system had to go negative, so Jupiter has a brightness of minus 2.7, a bright Moon is minus 12 and the Sun minus 27!

In theory, the faintest object you can see with the naked eye is magnitude 6 but in Alvechurch it’s a struggle to see below 4. Binoculars can take you down to about 8 and my best telescope sees down to 11. The supernova in the Big Dipper was about 10 so a good telescope is needed to see it. Still, the International Space station is always negative so is always brilliant.


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