Home > Constellations, Ephemeris Program, stars, Summer Solstice > 12/15/2015 – Ephemeris – Procyon the star that’s “Before the dog”

12/15/2015 – Ephemeris – Procyon the star that’s “Before the dog”

December 15, 2015

Ephemeris for Tuesday, December 15th.  The Sun will rise at 8:13.  It’ll be up for 8 hours and 49 minutes, setting at 5:02.   The Moon, 3 days before first quarter, will set at 9:48 this evening.

Visible low in the east at 9:30 p.m. appears the star Procyon to its lower left is Sirius the brightest night-time star.  Procyon is the bright star in the constellation Canis Minor, or lesser dog.  I can find only one other star in Canis Minor.  Perhaps it’s a hot dog.  If Sirius, in Canis major is the Dog Star then Procyon should be the Little Dog Star.  However Procyon is an interesting name.  It means “Before the dog”, which is an allusion to the fact that Procyon, though east of Sirius actually rises before it.  This is due to Procyon’s more northerly position.  This effect doesn’t work south of the equator, however.  Sirius will rise at about 9 tonight.  Procyon is a star much like Sirius but is 32% farther away.  It’s 11.4 to Sirius’ 8.6 light years away.

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


Procyon, Sirius and the stars of winter. Created using Stellarium

Procyon, Sirius and the stars of winter. Created using Stellarium

In the above chart, beside the constellation lines, we have the grid of right ascension, from lower left to upper right; and declination, from upper left to lower right.  right ascension lines are like longitude on the Earth, while declination lines are latitude lines.  They are tipped because I don’t live at either the equator or one of the poles.  As the Earth rotates the Sun, stars and planets slide westward in the direction of the declination lines.  Note that Sirius is closer to the horizon than Procyon.  Also that Sirius is west of the 7 hour right ascension line. (Take my word for it.)  Procyon is  east of that line, thus Sirius is west of Procyon.

Other cool things can be seen in the chart.  Note the declination line that touches the horizon at the east compass point and runs just above Orion’s belt.  It is 0º declination, or the celestial equator.  It extends to the west compass point on the western horizon.  The Sun on the equinoxes will rise due east and set due west.  The 6 hour right ascension line runs past Betelgeuse in Orion.  At 23½º north declination, near Castor’s big toe in Gemini is where the Sun appears on the first day of summer, the summer solstice.

P.S. It was cloudy and rainy the last two days.  Didn’t see a Geminid meteor again this year, keeping my record intact.

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