Friday, 4 March 2016

Two jewel boxes for the price of one

In my previous post I talked about the advantages of binoculars over telescopes. Here's an example of a view that would simply be unthinkable through a telescope: these two wonderful star clusters in the same field of view. They haven't got a name as such, or at least that I'm aware of, and are scientifically referred to as M46 (on the left) and M47 (on the right). They're located a bit to the left of the brightest real star in our sky, Sirius, in the obscure constellation of Puppis, the stern of the ship Argo. The differences between the two are striking and loyal readers of my blog will already have guessed that they are completely unrelated to one another. M47 is fairly young (78 million years est.), not too rich and its stars are still very bright and hot. M46 on the other hand is much more mature (300 million years est.) but also much richer with an estimated 500 members. The image also completely fools us because M47's actually much closer to us: 1.600 lightyears against 5.400. But here on Earth we see them very close to one another. Not quite close enough to admire them as a couple through a telescope, however. As I explained, telescopes magnify more and will never allow you to observe these two in the same field of view and at the high level of brightness of a good pair of binoculars. 

The image also hides a little surprise for keen observers. Dim the lights, relax and concentrate as if you were truly looking through a telescope. Focus on M46... towards the top of the cluster... (I'll leave you for a moment with this sketch and continue writing under the image)

Have you seen that tiny little faint patch? It's a planetary nebula! And... no, it has nothing to do with the cluster itself as it lies more than 2.000 lightyears closer to us. High-resolution photographs reveal that it has a very faint but large outer halo whereas the visible part marks the death of the red giant star in its centre. All that is left of the star is a small white dwarf which is in fact one of the hottest stars we know. It has a surface temperature of 75.000°C, compared to 5.500°C on the surface of our Sun! Next time we'll zoom in a little bit, so keep following this blog!

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