…continuedMining Hipparcos's Buried Treasure
What to Expect
For example, a well-known star that changes only rarely is Epsilon (e) Aurigae, the eclipsing binary whose companion comes around to hide part of the primary star only once every 27 years! The system then loses half its normal luster for 13 months at a stretch. These episodes, first noticed in 1821, happen only once for each new generation of astronomers. (Don't hold your breath; Epsilon's next eclipse isn't due to start until 2009.)
Other new variables behave quite differently. The light-curve fragment for HS Ursae Majoris, for example, shows a gradual rise in brightness (with minor ups and downs) from magnitude 8.9 at the start of 1990 to an apparent peak of 8.3 in November 1991. The star then faded back to the middle of this range by November 1992. Clearly it's an intrinsic variable, probably irregular, but only by continued monitoring can anyone really know.