Peanuts by Charles Schulz for November 21, 1961
November 20, 1961
November 22, 1961
Transcript:
Lucy and Linus are standing in the field looking up at the night sky with all the stars. Lucy says, "The biggest star measured so far has a diameter 2000 times wider than that of the sun." <br> <br> Linus turns and looks at Lucy as she says, "I wonder how they measured it..." <br> <br> the two continue looking at the stars in silence. <br> <br> Linus finally turns to Lucy and questioningly says, "With string?" Lucy just looks at him. <br> <br>
Astrophysicist Ethan Siegel explains how it’s actually done here:
https://www.forbes.com/sites/startswithabang/2017/06/10/ask-ethan-why-do-stars-come-in-different-sizes/
Basically, astronomers infer the size of a star by by measuring its temperature (which can be determined from its colour), its distance, and its brightness. Given that information, it is possible to infer its size. A red star (cool) that is very bright must also be very big, because it has to have a higher surface area to radiate so much even though its light emission is of lower energy, while a blue star (hot) that is the same brightness has to be smaller, since its emission for a given surface area has higher energy.