Archive for September 10, 2020

09/10/2020 – Ephemeris – The bright star Deneb will pass overhead tonight, what does that mean?

September 10, 2020 Comments off

This is Ephemeris for Thursday, September 10th. Today the Sun will be up for 12 hours and 45 minutes, setting at 8:01, and it will rise tomorrow at 7:17. The Moon, at last quarter today, will rise at 12:29 tomorrow morning.

Around 11 pm tonight the bright star Deneb in Cygnus the Swan and the northernmost star of the Summer Triangle will be overhead, or just about at the zenith. Just as on the Earth we have a coordinate system of longitude and latitude for position east-west and north-south, we have the same for the celestial sphere the imaginary sphere of the heavens east-west is called right ascension and north-south is declination. I’m going to ignore right ascension’s relation to longitude. Declination directly relates to latitude in that a star the with the same declination as your latitude will pass directly overhead. Deneb’s Declination is about 44 degrees 20 minutes north. Check the GPS on your smart phone to see how close your latitude is to that.

The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Celestial coordinates are actual projections of earthly coordinates. CNP = Celestial North Pole, CSP = Celestial South Pole are directly above the earthly poles. Same with Celestial Equator. Therefore a star or any celestial object passes overhead or at the zenith for locations with the same latitude on the Earth. That’s what the diurnal or daily circle is as the Earth rotates.