Home > stars > 02/11/2016 – Ephemeris – What do star colors reveal?

02/11/2016 – Ephemeris – What do star colors reveal?

February 11, 2016

Ephemeris for Thursday, February 11th.  The Sun will rise at 7:49.  It’ll be up for 10 hours and 15 minutes, setting at 6:05.   The Moon, 3 days past new, will set at 10:06 this evening.

The bright stars of winter have subtle differences in color.  But what do those colors mean?  In stars color is indicative of surface temperature.  From coolest to hottest are red, orange, yellow, and white to blue, the hottest.  Interior decorators may disagree, but that’s how it is.  Coolest of the bright stars is red Betelgeuse in Orion’s shoulder, then orange Aldebaran in the face of Taurus the bull, and Pollux in Gemini.  Hotter yet is yellow Capella in Auriga the Charioteer, about the temperature of the Sun.  Then we come to the white-hot Procyon and Sirius in the little and big dogs of Orion.  Hottest is blue-white Rigel in Orion’s knee.  There are hotter stars in Orion, the center and rightmost stars of Orion’s belt are bluer and hotter yet.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Bright stars of winter

Bright stars of winter with hints as to their colors.  The star label is the color of the star. Created using Stellarium.

Color vs. Surface Brightness

A table of star color and surface temperatures. Created from data in Wikipedia.

The star Alnilam is the center star of Orion’s belt, while Mintaka is the rightmost star of the belt.  The temperature scale K is the Kelvin scale which is the Celsius scale plus 273.15.  Zero on the Kelvin scale is absolute zero.  1 degree Celsius equals 1 Kelvin.  One never says degrees Kelvin.

Betelgeuse is a variable star, so its surface temperature varies.

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