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Wandapec (June 20, 2009, 17:47:22 PM):
I saw this on Phil Plait's blog the other day. I've watched it over and over. It is just mind blowing!

Watch it here.
Tweefo (June 21, 2009, 10:25:36 AM):
How can one save a You Tube movie so that you can look at it off line?
Wandapec (June 21, 2009, 12:08:00 PM):
How can one save a You Tube movie so that you can look at it off line?

If you Google "Youtube video download", you will get lots of options. I have just tried this one - Youtube Catcher, and it works brilliantly. Just follow the instructions - paste the video address in the box and click download. You then right-click the link and save the file with a .flv extension. I played it using VLC media player, my preferred player.

Rigil Kent (June 21, 2009, 16:03:05 PM):
Realplayer also does the job nicely. A "download tab" pops up when you hover over the Youtube clip.

Wandapec, many thanks for posting the link, it really is awesome.

But it did give me something to be provisionally sceptical about ;) , and that is: how can astronomers be so sure of these sizes?

We cannot observe and measure the disk of these stars like planets through a telescope, with Betelgeuse as a possible exception.

We can gather the star's spectrophotometric data. From that, the scientists can infer the chemical composition, and velocity. Paralax measurements will tell us the distance of closer stars. But size? How on earth can they measure that? Oh, and the mass for that matter.

I know I'm wrong, just not sure in what way. ???


Mefiante (June 21, 2009, 17:03:40 PM):
In a nutshell, gravitational redshift. It’s a little more complicated than a direct calculation because it involves several unknowns that are solved for simultaneously as a system from a set of measured observables. Known binary and multiple star systems are often used to confirm calculated parameters.



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