Wednesday, 6 January 2016

NGC869-884, the sparkling double cluster in Perseus

When you take out your camper bed in autumn (don't forget that warm blanket and a hot cup of tea), look to the east. You will easily notice the constellation of Cassiopeia, which doesn't really look like the old queen from Greek mythology but rather like a bright, slanted W. Now if you take the left lower point of the "W" and go down a little bit, you will notice that there's a faint little patch, at first not that easy to see with the naked eye. Take your ordinary 10x50 binoculars and point at it. Go on! It'll make your jaw drop! 

Here's my impression with my somewhat bigger 100mm astronomical binoculars and a couple of 8mm TeleVue Delos eyepieces (resulting magnification 63x):

What you see are two open clusters of stars which lie at a distance of a whopping 7.500 lightyears, meaning that light, with its formidable speed, needs 7.500 years to travel from those clusters to Earth. The term "open cluster" means that the individual stars in it can be resolved quite easily, contrary to a "globular cluster" which is much denser and can only be resolved with larger telescopes. Open clusters also lie within our galaxy whereas globular ones are in fact a kind of "mini galaxies" which accompany our own. These particular open clusters are also still very young, with their age estimated at less than 13 million years. In comparison, the famous Pleiades, also still young, have an estimated age ranging from 75 to 150 million years. Therefore the thousands of stars in these clusters are incredibly hot and it is very unlikely that we'll find extraterrestrial life there because planets probably still haven't formed and the vicinity of so many hot stars would make any planetary surface quite unfriendly. But that's exactly why these fairly remote clusters are so bright and sparkling. I'm sure that you'll want to see them again and again.

About the drawing itself, the original was made with a simple pencil on white paper, which I subsequently inverted and edited in Photoshop to render it as realistic as possible. You can imagine that given the enormous amount of stars I've spent about 2 hours behind my binoculars in order to draw them all. One of the main difficulties with drawing rich and complex clusters is that eventually your head will start to spin and you wonder whether you've already drawn a certain tiny little star or not. You'll start seeing stars all over the place and think that you're about to go crazy! :-) Another difficulty is that with time, the image in the binoculars will rotate, as the sky moves along with the rotation of the Earth. So the references you use to determine the position of the stars for your drawing will rotate likewise and this creates a lot of confusion. But in the end I'm quite pleased with the result and I hope you like it too.

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