Home > Ephemeris Program, Observing, Stars > Ephemeris: 07/28/2025 – Deneb, a truly brilliant star

Ephemeris: 07/28/2025 – Deneb, a truly brilliant star

July 28, 2025

This is Ephemeris for Monday, July 28th. Today the Sun will be up for 14 hours and 48 minutes, setting at 9:12, and it will rise tomorrow at 6:26. The Moon, halfway from new to first quarter, will set at 11:06 this evening.

This evening when it gets dark enough 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 higher in the east, while Altair is lower in the southeast. Deneb’s apparent magnitude, or brightness as seen from Earth, is deceptive. Its vast distance of possibly 2,600 light years is over 100 times the distance of Vega. If brought as close as Vega, Deneb would be almost as bright as the quarter moon. It is possibly as bright as 200 thousand Suns; and a huge star, possibly as large as half the diameter of Earth’s orbit. For all this, it is only 19 to 25 times the mass of the Sun.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.

Addendum

Cygnus finder animation
Animated Cygnus finder chart. Included also are, beside Deneb, the other stars of the Summer Triangle: Vega and Altair and their constellations Lyra the harp and Aquila. See if you can find them. Created using Stellarium.
The ultraviolet light given off by Deneb is causing the nearby nebulae, rich in hydrogen to glow.
The intense ultraviolet light given off by Deneb, at the upper right edge, is causing the nearby hydrogen rich nebulae glow their characteristic red color. The North American Nebula is on the left, and the Pelican Nebula is to the right of it. The North American Nebula can be descerned with the naked eye just below Deneb as seen in the summer as a faint glow, though not its shape. Credit: KPNO/NOIRLab/NSF/AURA/Adam Block (CC BY 4.0)

Categories: Ephemeris Program, Observing, Stars Tags: , ,