Some celestial yardsticks are visible in the night sky

The stars Vega, 61 Cygni and Delta Cephei are located near the zenith, or the point directly overhead, around 8 p.m. local time as seen from mid-northern latitudes.  (Image credit: SkySafari app)

One of the questions I am sometimes asked is, “How do astronomers know how far away a star or a distant galaxy happens to be from Earth?” In our sky this week, there are three stars that have been used to demonstrate how to measure stellar distances: Vega, 61 Cygni and Delta Cephei.

Step outside at around 8 p.m. local time as the sky is getting dark, look straight up above your head and you’ll see Vega in the constellation of Lyra, the lyre, shining with a brilliant, bluish tinge. It’s the second-brightest star of our current evening sky. 



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