Although Errai (Gamma Cephei) in the constellation Cepheus only rates as a third-magnitude star, it is fairly easy to find, and quite visible in a dark country sky. To many stargazers, Cepheus looks like a child’s depiction of a house, with Errai marking the peak of the roof. Try your luck and see if you can star-hop to Errai, the future North Star, tonight!
First of all, use the Big Dipper “pointer stars” (Merak and Dubhe) to locate Polaris, the present-day North Star. Then jump one fist-width beyond Polaris to hop on over to Errai. (Hold your fist at arm’s length.)
The 26,000-year precession cycle causes the north celestial pole to move counter-clockwise in front of the backdrop stars at about one degree every 72 years
Cepheus the King is not a particularly prominent constellation. But you’ll know that you’ve found Cepheus, because you’ll see his more striking wife – the M or W-shaped constellation Cassiopeia the Queen – standing at his side. Errai is nearly on line with the stars Polaris and Caph of Cassiopeia (see sky chart at top of page).
For most of the Northern Hemisphere, orange Errai shines as a circumpolar star. Circumpolar stars are stars that neither rise nor set, but always appear above the horizon.
Polaris will continue to reign as the Northern Hemsiphere’s pole star for centuries to come. Yet Polaris won’t remain the North Star forever. Errai stands next in line to inherit the title. Errai will most closely mark the north celestial pole around 4000 AD. Alderamin – Cepheus’ brightest star – will become the northern pole star around 7500 AD.
Animation showing 26,000-year precession cycle relative to backdrop stars. Image credit: Wikimedia Commons
Errai is a binary star – two stars revolving around a common center of mass. It’s one of the few binary stars known to harbor a planet.
