02/16/2015 – Ephemeris – The little Dog Star
Ephemeris for Tuesday, February 16th. The Sun will rise at 7:42. It’ll be up for 10 hours and 29 minutes, setting at 6:12. The Moon, 1 day past first quarter, will set at 3:45 tomorrow morning.
Procyon is the bright star to the east or left of Betelgeuse in the sky tonight, which puts it in the east-southeast at 9 tonight. Procyon is the brightest of the two stars in Canis Minor, Orion’s little hunting dog. Procyon is sometimes called the Little Dog Star for that reason. The Dog Star Sirius is a ways below and right of it. The name Procyon means “Before the Dog”, because Procyon, though east of Sirius, rises before it due to its more northerly position. This only works if one is north of 30 degrees north latitude. South of that, Sirius rises first. Procyon is a white star 11 and a half light years away, 3 light years farther than Sirius, and like Sirius it has a faint white dwarf companion. It’s a bit less than half the Sun’s age.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Note that at their rising Procyon is higher in the sky than Sirius.
There are some grid lines on the chart. The ones running from lower left to upper right are lines of declination, which are like latitude lines on the Earth. On this chart they are 10º apart. The line that intersects the horizon at the east compass point is the celestial equator. It will meet the western compass point at the horizon. As the Earth rotates the stars and planets will move westward in the direction of these declination lines. The lines that run from upper left to lower right are hour lines of right ascension. Here they are 15 degrees or one hour apart, The Earth rotates 360º in a sidereal* day. 360 divided by 24 hours gives 15º an hour. So the celestial sphere of stars and planets will slide 15º westward in a sidereal hour.
* A sidereal day, rotation with respect to the stars, is about 4 minutes shorter that the solar day, the day and time we keep based on the Sun. The Sun moves about one degree eastward each day, so the rotation has to catch up that one degree each day. The rotation of one degree takes 4 minutes. I’ll let you work that one out for yourself.