I should have known that when I said on Friday "The skies are clear and nothing can stop me now."(previous post) this was sure to bring the curse of 4AoS down upon me, and indeed the clouds immediately rolled in and stayed rolled in for 4 days.
Last night the BBC predicted total cloud cover with not the slightest chance of a break, so of course the skies were clear. As is almost always the case, the rare occasions when the clouds do clear also almost always coincides with the rare occasions when you have other things planned, and so it was last night. But I DID get half an hour to myself to drag the telescope out, attach the SA100 Star Analyser, and set up the camera, and here is my first ever spectrum of starlight:
The star, visible on the right side, is Betelgeuse.
The spectrum is quite pretty but it's also a long way away from revealing any useful information. The first problem is that it's very overexposed so the subtle detail is lost.
Here's a later attempt of the star Sirius:
This shows another problem which is that the firing of the shutter wobbles the camera, blurring the image (see the star isn't sharp and the line of the spectrum isn't clear)
After Photoshop:
The really important information revealing the chemical composition of the star is contained in the dark lines (more on that later) but if we compare the spectrum to a better one of Betelgeuse, we can already see something interesting:
The spectra look quite different.
What's going on here?
If you take a metal bar and heat it up the atoms gain energy and they give off radiation with very long wavelengths. This is infrared radiation and with an infrared camera you can see warm objects glowing in the dark. As it gets really hot it will begin to radiate more of its energy in the shorter wavelengths and the bar will glow in the visible spectrum. What colour? A deep red.
As it gets even hotter the body will radiate more energy at shorter wavelengths and it will become more orange-coloured, then yellow, and eventually a blue-white colour. At this point it is giving off most of its energy in the green and blue part of the spectrum.
A new star is very hot and gives off a lot of energy, then as it get old, like most of us, it produces less energy. So by looking again at the 2 spectra together, what can you say about Sirius and Betelgeuse?
Careful now, there may well be a short written test on this stuff in the future.
I'm sure you noticed that Sirius is much brighter in the higher end of the green and blue area, and much dimmer at the red end. Betelgeuse on the other hand is very bright at the red end and the light falls off at green and blue end.
So which is the old star and which is the young one?
Sirius is very young in star years; 200 - 300 million years old, and it's very hot; around 10,000K at the surface. Betelgeuse on the other hand is right at the end of its life and is around as third as hot as (Sirius 3000 - 3500K) It is around 10 million years old, which is also very young for a star, so the fact that's it's on its last legs is something of a puzzle. It's probably evolved quickly because of its vast mass. Live fast die young.
Now I need to get to grips with the software which will allow me to callibrate the images and turn them into proper date. Watch this space, though it make take time; I read that the learning curve is steep...
Recent Comments