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Find the Planets
The dream of finding worlds beyond our solar system is now a reality. In 1992,
 Alex Wolszczan and Dale Frail announced the landmark discovery of planets
orbiting a distant pulsar. Three years later, Michel Mayor and Didier Queloz
ended the long quest to detect a planet around a star like our own sun. The
pace of discovery since then has been astounding -- heralding nearly a dozen
new alien worlds.
Now you can join the planet hunt by locating some of the brighter stars with
known planetary systems on a map of the sky. If conditions are right, you might even
spot the actual stars in the night sky.
You Can't See Them -- But They're There
 Even with the most advanced telescopes, astronomers cannot image the planets
beyond our solar system directly. They see evidence for their existence in the
wobble of stars pulled by their gravity. The movement is so subtle that it's
difficult to detect visually. So, some astronomers look for periodic shifts in
the frequency of a star's light -- using a technique called Doppler
spectroscopy. Other scientists listen to distant pulsars for the telltale sign
of an irregular beat.
Follow The Stars
The planets themselves may be impossible to see, but you can locate some of the
stars at the heart of planetary systems. Knowing star names can point you in
the right direction, because the name of a star often refers to its location
within a constellation. For instance, 51 Pegasi, the first sun-like star to be
found with an orbiting planet, lies in the constellation Pegasus.
 Whether or not a star can be spotted easily in the night sky depends on its
apparent brightness, or magnitude. Magnitude is signified by a numerical value,
and the dimmer the star, the higher the number. The brightest star in the sky,
Sirius, has a magnitude of -1.5, while stars with magnitudes higher than about
4 are difficult or impossible to perceive with the naked eye.
The stars listed below are just at the border of visibility with the naked eye. With
our limited vision, we can locate their approximate place in the sky, using
constellations to guide the way. But to clearly pinpoint these stars, you may
need binoculars or a small telescope.
This star, 78 light years away, lies on the border of the constellation
Virgo. In January of 1996, Geoff Marcy and Paul Butler announced their
discovery of a massive planet -- over six times the size of Jupiter -- orbiting
70 Virginis. The planet's surface temperature is estimated at 85 degrees
Celsius, well within the range for liquid water. But the massive planet is
likely a lifeless gas giant. If this alien world has moons, they may be more
hospitable to life.
See where Virgo lies on the Star Map.
Lying near the Big Dipper in the constellation Ursa Major, this star may be the
easiest for amateur sky watchers to locate. Announced at the same time as 70
Virginis, its orbiting planet is a third the size and, with a surface
temperature of -80 degrees Celsius, considerably cooler. The planet lies
roughly twice as far from its parent star as the Earth does from the sun.
See where Ursa Major lies on the Star Map.
When Mayor and Queloz first described the planet they had discovered around 51
Pegasi, many astronomers were stunned. It raced around its parent star in a
4.2 day orbit -- putting it 500 times closer to its star than the Earth is to the
sun. This broiling world challenged previous notions of where a Jupiter-sized
planet would be found.
Pegasus, marked by its distinctive Great Square, is known as an autumn
constellation. See where Pegasus lies on the Star Map.
Geoff Marcy and Paul Butler were among the scientists surprised by 51 Pegasi.
But in April of 1996, they found another massive planet orbiting close to its
sun. The planet around 55 Cancri orbits every 14.76 days -- far more quickly
than our own speedy Mercury.
See where Cancer lies on the Star Map.
Photo (1) copyright © John Whatmough, JTW Inc; (3) copyright © STScI/NASA. Visualization (2) produced by the Cornell Theory Center based on
research by Alex Wolszczan, Penn State. Sky charts adapted from John Whatmough, JTW Inc.
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