Friday, 15 December 2017

IC417: the yellow spider

Rounding off my series about vast and faint nebulae in Auriga, I present you with IC417, otherwise known as the Spider Nebula. Again, it's not an easy object for visual astronomers but with a sufficiently dark sky and generous aperture you should be able to spot it. Although the nebula is a hot star forming region and would therefore benefit from the use of filters, I decided to make my observation without as I shall explain. 

The nebula complex lies somewhere around 7,500 light-years away, in the outlying Perseus arm of our galaxy. As I said, it is another giant stellar nursery in the heart of which we find a lovely, somewhat elongated cluster of young stars, denominated Stock 8. Interesting to note is that these young stars seem to have different ages, ranging from 1 to 5 million years, which indicates that stellar formation has continued over a long period of time here. 

Now let's turn our attention to the bright, yellow star which appear to be the protagonist of this sketch. As you might have guessed, this star (Phi Aurigae) is much closer to us, at a distance of 450 light-years, and is already visible to the naked eye under suburban skies (mag. 5.05). It is an orange giant (although I saw it rather as bright yellow), meaning that it has evolved off the main sequence and is now fusing helium into carbon and oxygen. Although nearly 300 times as bright as our Sun and 31 times its diameter, it does bear a lot of similarities to our star. For starters, it weighs in at 1.2 solar masses and it has a very similar chemical composition. In fact, it's a perfect example of how our Sun will look like in about 5 billion years, after it'll have consumed all of its core hydrogen.

I guess this is just an optical illusion, caused by the brightness and deep colour of Phi Aurigae, but I had the impression that the nebulosity in its immediate vicinity also had a slight yellowish hue. The sight was so lovely that I wanted to capture it this way, rather than to use nebula filters which make all stars appear blue.

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