07/27/2015 – Ephemeris – Deneb, the dimmest of the Summer Triangle stars. But is it really?

Ephemeris for Monday, July 27th.  The Sun rises at 6:23.  It’ll be up for 14 hours and 51 minutes, setting at 9:14.   The Moon, 3 days past first quarter, will set at 3:36 tomorrow morning.

This evening when it gets dark the bright star Deneb in Cygnus the swan will be high  in the east northeast.  Deneb is the dimmest star of the summer triangle.  Of the other stars of the triangle, Vega is very high in the east, while Altair is lower in the southeast.  While Deneb’s apparent magnitude, or brightness as seen from earth, makes it the dimmest of the three bright stars, Deneb’s vast distance of possibly 2,600 light years makes it over 100 times the distance of Vega.  If brought as close as Vega, Deneb would be almost as bright as the full moon.  It is as bright as two hundred thousand suns.  It apparently has run out of hydrogen in its core.  Once a blue super giant star, it’s currently evolving through the white supergiant stage.

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

Addendum

The Summer Triangle. Created using Stellarium and The Gimp.

One of my old photographs of Deneb and the North American Nebula digitized from a slide.

The Hertzsprung-Russell diagram of star luminosity vs. surface temperature. Note that Deneb is at the top center, while the Sun is lower on the main sequence. Credit: European Southern Observatory (ESO).