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A Tour of Planetary Systems in the Night Sky
 
Artist's concept of the star Iota DraconisClick here for larger image.
 
Artist's concept of the Iota Draconis planetary system
 
 
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(PLANET QUEST) -- Did you know that when you walk outside and look up on a clear night, some of the stars you see with your naked eye are circled by planets? While you can't actually see the planets themselves, you can locate several stars at the heart of other planetary systems -- without using a telescope.

The following tour will introduce you to four of the brightest extrasolar systems, meaning planetary systems beyond our own solar system. You can locate them in the night sky this month by using our printable sky map. Some of these stars are just on the border of visibility, but you can find their approximate place in the sky. To see them clearly, you may need binoculars or a small telescope.

(For a multimedia tour of extrasolar planets in the night sky, see NASA's 3D New Worlds Atlas.)

Iota Draconis

The first stop in our tour is the giant star Iota Draconis. With a magnitude, or apparent brightness, of 3.3 it can easily be spotted with the unaided eye on a clear night. The Iota Draconis system is located 100 light-years from Earth in the constellation Draco, the dragon. If you connect the "dots" in this constellation, this star forms one of the joints in the dragon's body.

The planet circling this star is a gaseous giant, about eight-and-one-half times the size of Jupiter. It was discovered in 2002.

The host star is not like our star, the Sun, but is an old star that has already burned the hydrogen fuel in its core. This discovery provides evidence that planets at distances from their stars comparable to Earth's distance from the Sun can survive the evolution of the host star into a giant.

Tau Boo

This star is located 49 light-years away in the constellation Bootes, the herdsman. You can easily find Bootes by following the Big Dipper's handle. Bootes is a diamond-shaped constellation and contains the fourth brightest star in the sky, Arcturus. The star Tau Boo is located near the diamond's point, and is barely visible to the eye, with a magnitude of 4.5 (the higher the magnitude, the dimmer the star appears).

The planet circling Tau Boo, discovered in 1996, is nearly four times as large as Jupiter.

Upsilon Andromedae

Digitized Sky Survey image of the star Upsilon AndromedaeClick here for larger image.
 
Digital Sky Survey image of the star Upsilon Andromedae, which is orbited by three unseen planets
 
The Upsilon Andromedae system is located 44 light-years from Earth in the well-known Andromeda constellation. It contains at least three planets, and is one of the first multiple-planet extrasolar systems discovered.

All three planets that circle the star are gas giants. One of them, known as a "hot Jupiter," is located extremely close to the star and completes its orbit every four-and-one-half days. The second planet is located slightly closer to the star than Earth is to the Sun, while the third orbits at about twice that distance.

This system is located around the knees of the princess, but at magnitude 4.1 is at the limit of what you can see from suburban skies.

70 Virginis

This Sun-like star is located 59 light-years away in the constellation Virgo, the virgin, near Bootes. At magnitude 5, this is the most challenging of the four stars on this tour. Each step up in magnitude is a change in brightness by 2.5 times.

Astronomers Geoff Marcy of San Francisco State University and Paul Butler of the Carnegie Institution announced the discovery of a giant planet more than six times the mass of Jupiter orbiting 70 Virginis in January 1996. Their discovery helped usher in a new era of extrasolar planet observations. To date, this worldwide quest has led to the discovery of more than 100 planets orbiting stars other than the Sun.

Future NASA missions such as the Space Interferometry Mission and Terrestrial Planet Finder will be able to search for much smaller and potentially habitable planets that may exist around stars such as these.

(Click here for August sky map.)

 

Written by Randal Jackson / PlanetQuest

 
 
NASA's PlanetQuest