posted on Jan, 10 2014 @ 08:05 AM
reply to post by ErosA433
Betlegeuse, is a red super giant. It's cooler than our sun, but larger than our solar system's entirety.
Color, goes along with temperature, but it does not go along with size. In fact as our star cools, it will expand, and become less dense.
Indeed though I was speaking of the main sequence and not the giant and sub-giant branch. And Betelgeuse is big, but not THAT big... it extends
somewhere between Mars and the Asteroid belt, from the most recent estimates id seen.
Giants are relative rarities because they are short lived in the grand scheme of things. On a HR diagram, the mains sequence stars peel off of the
main-sequence and move off into the sub-giants branch. Truly enormous stars of the mains sequence don't live all that long, and spend a short period
on the main sequence and then move straight into super-giant territory, some of which don't explode at the end of life, they just blow off all their
outer material and fade away. The luminosity and colour of the giant branch is also used to date star clusters, as if all stars are born at around the
same time and are of similar size (remember the statement regarding the sun?) then it follows that the older the cluster, the cooler the giant branch.
It does reach a limit however because very red and very small stars go on living for what seems like forever, never swelling or expanding, they just
slowly fade away.
The lives of stars and all their different types is pretty amazing.
If you are looking at a main sequence star (can be determined by spectral type) and you know the distance, you can use the relative luminosity to
calculate an estimated size.
Pretty basic, you look at two red stars that are at the same distance, they appear to be the same temperature, except one is giving you 10x more
light. The brighter one is thus larger.
edit on 10-1-2014 by ErosA433 because: (no reason given)
edit on 10-1-2014 by ErosA433
because: (no reason given)