November's star, Alpheratz

This month look for the star, Alpheratz, the lucida, or brightest star of Andromeda. Alpheratz is one of the few stars connecting together two constellations. In this case, Alpheratz units the constellations of Andromeda and Pegasus. Alpheratz passes just south of the overhead position at 9:00 PM in early November and about two hours earlier in late November. Alpheratz is 97 light years, so if you know someone born in 1916, Alpheratz is his or her birthday star this year.

The surface temperature of Alpheratz is approximately 23,000 degrees F (making it what astronomers call a class B star). Being 150% hotter than the surface of our sun, Alpheratz produces significantly more ultraviolet radiation than the sun. In addition to producing more ultraviolet radiation, the star is producing 200 times more radiation than our Sun. To emit this amount of radiation, Alpheratz must be more massive than the sun. As a result of this additional mass, mathematical calculations predict that Alpheratz will live a shorter life than the Sun.

Alpheratz is not alone in space. It has a companion star with an orbital period of 97 days. Alpheratz is too distant and its companion too close for telescopes to see the two stars separately. Astronomers determine that stars like Alpheratz are binary stars by measuring the variations occurring in their combined spectra. The lines in the spectra of Alpheratz shift back and forth over a period of 97 days, giving away the fact that there are two orbiting each other in this period of time. We call stars like these spectroscopic binaries because of the way astronomers detect them.