01/30/2012 – Ephemeris – Getting Sirius about color
Ephemeris for Monday, January 30th. The sun will rise at 8:04. It’ll be up for 9 hours and 43 minutes, setting at 5:47. The moon, at first quarter today, will set at 1:51 tomorrow morning.
The bright star shining so bright low in the south southeast at 9 p.m. is Sirius the Dog Star. I talked about it Friday in the context of its constellation Canis Major, Orion’s larger hunting dog. Sirius itself is a remarkable star. It’s name means dazzling one and a look at it in binoculars or a telescope will prove it.. The twinkling effects are due to the earth’s atmosphere, but the bright arc light color is all his. Sirius is a perfect white star. Compare it with the brightest star now overhead Capella which has the same color as our sun. Star colors tell us the temperature of the star surfaces, which run from cool red to hot blue. On our Fahrenheit temperature scale, the sun’s surface is about 10,000 degrees, Sirius is nearly twice that.
* Times, as always are for the Traverse City/Interlochen area of Michigan.
Addendum
Orion and his Hunting Dogs. Created using Stellarium.
Sirius actually looks blue-white to me. Of course during the day our yellow sun looks white. I think it has to do with out night vision.
