Home > Asterism, Ephemeris Program, Stars > 07/21/2015 – Ephemeris – Vega, the brightest star of the Summer Triangle

07/21/2015 – Ephemeris – Vega, the brightest star of the Summer Triangle

July 21, 2015

Ephemeris for Tuesday, July 21st.  Today the Sun will be up for 15 hours and 3 minutes, setting at 9:20.   The Moon, 3 days before first quarter, will set at 12:01 tomorrow morning.  Tomorrow the Sun will rise at 6:17.

The bright star high in the east is Vega, one of the stars of the Summer Triangle an informal constellation called an asterism. Vega belongs to the official constellation Lyra the harp, which includes a narrow parallelogram of stars to its south. Vega was regarded by astronomers as a standard calibration star. Though a first magnitude star, its actual magnitude is 0.03 and slightly variable. It is a type A0  (A-zero) pure white star, and is 25 light years away. Astronomers however got a shock in 1983 when calibrating the Infrared Astronomy Satellite (IRAS) on it: Vega showed an excess of Infrared radiation that means the star is orbited by a disk of dust, perhaps the beginnings of a planetary system.  Due to the slow wobble of the earth’s axis Vega will be our pole star in 14 thousand years.

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


The Summer Triangle July 5, 2012 at 11 p.m. Created using Stellaruim and The Gimp.

The Summer Triangle. Created using Stellarium and The Gimp.


Magnified view of Lyra. Created using Stellarium.


Vega in the mid-infrared from the Spitzer Infrared Satellite. Credit: NASA/JPL-Caltech/University of Arizona

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