Tuesday, 1 March 2016

There's an Eskimo in Gemini

I'm sorry, my dear Inuit friends, if the title of my message sounds a bit derogatory but I wasn't the one who invented the name of the object I'd like to talk about today. Irony aside, it does look a bit like a head surrounded by a parka hood, doesn't it (here seen lying down)? I already explained what planetary nebulae are in my message about the Crystal Ball and that's exactly what the Eskimo Nebula, or scientifically denominated NGC2392, is. The star inside of it was once very much like our own sun in terms of size and overall aspect but unfortunately it has reached the end of its life. Nuclear fusion became unstable and its atmosphere's blowing away into space. Already with a reasonably small telescope it's possible to distinguish the two main gas shells which give the Eskimo its peculiar shape. Very large telescopes reveal that the outer shell consists of unusual lightyear-long filaments, like sunrays around the star. The inner shell's also much more complex than what my home-built telescope could make me see and in reality looks a bit like a ball of twine or a sort of bubbly fishnet structure around the dying star. We estimate that the star began to fall apart some 10.000 years ago, so more or less around the time when humans started to abandon their roaming hunter existence and became settlers. When thinking in stellar terms, wouldn't you say that this nebula developed itself pretty quickly? The gas is expelled at a speed of a whopping 300.000 kilometres per hour and will eventually dissipate into space, while the star will cool down and extinguish.

Another interesting quality of planetary nebulae is that they usually have a very high surface brightness. They're often bright enough to show colour when observed through a telescope! In general our eyes are able to make out a blue-greenish hue in most of these small but bright objects, which corresponds to the presence of hydrogen (greenish) and oxygen (blue) in the nebula. It so happens that blue is also the colour to which our eyes are most sensitive in the dark. Let's just say that we're in luck! 

The sketch itself is already a couple of years old and it's not one of my best, according to my opinion. But this nebula's one of the easiest and brightest in the sky and definitely one of winter's favourites, so I couldn't just skip it.


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