Monday, March 18, 2013

How big do stars look from habitable planets around them?

Standing on a habitable alien world, how big would that planet's host star look overhead? After a quick Googling, I didn't come up with any nice summaries. So I snagged Allen's Astrophysical Quantities and did a couple quick calculations.

This figure is the result, showing the apparent sizes of stars as seen from hypothetical habitable planets. around them, all scaled to the size our Sun appears in the Earth's sky. The estimates are fairly crude; I just approximated the distance at which the (bolometric) flux from each star would be equal to that which Earth sees from the Sun. This ignores complicating factors like effective albedo changes due to different peak wavelengths produced by each star, or tidal locking for close-in planets around the lowest-mass stars.

I added the approximate masses of a few notable stars on the left-hand side. Only a couple of these are known to have planets. 

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