Upsilon Andromedae, a star in Andromeda, is the first star aside from the Sun known to have more than one planet orbiting it. One of several dozen stars now know to have large planets in orbit, Upsilon Andromedae has three planets similar in mass to Jupiter, and possibly others below our current abilities to detect them.

Upsilon Andromedae is, in many ways, similar to the Sun. It's slightly whiter and hotter (spectral type F8V, for the astrophysically savvy), and it is about three times more luminous. In principle, a planet similar to Earth could exist around a star like this -- it would just have to orbit somewhat further from Upsilon Andromedae than the Earth does from the Sun. Right now, we lack the instrumentation to detect Earth-size planets around other stars, so whether Upsilon Andromedae has such planets is an open question.

Upsilon Andromedae is visible without a telescope: in the United States and other Northern Hemisphere sites, it's best seen during the fall and winter. It's not an especially bright star -- it's only about one-fifth as bright as Polaris, the North Star, so you'll need a fairly dark sky to see it well. Nevertheless, it is brighter than most other stars known to have planets, and hence one of the easiest to find.

Upsilon Andromedae Renditions

1. Here's a rendition of the Upsilon Andromedae system with a Hipparcos-based starfield. One of the Jupiterlike planets is in transit across the star's disk, which is somewhat hotter (whiter) and more luminous than the Sun's. Although the size, orientation, and coloring of the planets necessarily involve considerable artistic license, the star background is as accurately determined as existing data (mostly from Hipparcos) allow.

2. The Sun's actually in this starfield -- can you guess which star it is? Check out the same image with text labels to see if you were right.

3. The Big Dipper as seen from Upsilon Andromedae. The five central stars, which are actually grouped together in space, appear much as they do from Earth; by contrast, Alkaid, the star that would be at the end of the handle, and Dubhe, the one at the end of the bowl, are really in different locations in space from the rest. This isn't readily seen from Earth, but from here, the difference in star positions is enough to destroy the familiar Dipper shape.

4. Orion from Upsilon Andromedae. It's still recognizable -- its stars are far away enough that the 44 light-year trip to Upsilon Andromedae doesn't totally rearrange them -- but it's warped in places. In particular, the star Bellatrix, which makes up the left "shoulder" of Orion as seen from Earth, is closer than the rest and now is in an
   unfamiliar place. Also, traveling to Upsilon Andromedae takes us about 1/3 of the way to the Hyades, a star cluster in Taurus, which thus seems much larger and brighter. The Hyades is the large group of stars above and slightly to the right of Orion.