What to Expect

Keep in mind that some of these stars may stay constant for months or years before showing any sign of variability. The mere fact that no one noticed their variations in the past argues that they are leisurely performers. The 3½-year Hipparcos mission simply didn't last long enough for their light curves to be established with any certainty.

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.)

Similar behavior — a normally constant star with occasional abrupt dips — seems to be what's going on with FM Leonis, V353 Hydrae, and GV Draconis on our list. The Hipparcos satellite viewed any given star on about 100 to 150 irregularly spaced dates during the 1989-93 mission. Astronomers discovered that V353 Hydrae had quite a sharp eclipse around December 18, 1991. When this star will dip again, no one knows.

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.