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How do we know how massive stars are?

8 Jul 2015, 11:24 UTC
How do we know how massive stars are?
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How do we know how massive stars are?
Mitch, London

As we discussed in the previous vlog our understanding of stars is still incomplete, but there are areas which we are very confident on what we know.
In general we tend to know three things about stars: their brightness, their spectrum, and if they are close enough or of known luminosity, we can also know their distance.
If the stars are close, the distance is calculated using the parallax technique. By measuring the angle between the sun, the star and the earth at opposite times of the year, one can calculate the distance using simple trigonometry. If the star forms an angle of 1 arcsecond (1/3600th of a degree) then its distance is 3.26 light years. This is what we call a parsec (parallax of one arcsecond). If somebody were to claim to have crossed an asteroid field in, let’s say, 12 parsecs, then you’d know they took just over 39 light years to do so.
The spectrum gives us information regarding the composition of the stars. Knowing the elements beyond hydrogen that are in stars is important to determine their age.
And finally the brightness. The ...

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