Jan. 9, 2006

Erica Hupp 
Headquarters, Washington 
(202) 358-1237 

Donna Weaver 
Space Telescope Science Institute, Baltimore 
(410) 338-4493 

David Aguilar 
Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. 
(617) 495-7462 

RELEASE: 06-004

THERE'S MORE TO THE NORTH STAR THAN MEETS THE EYE

By stretching the capabilities of NASA's Hubble Space Telescope to the 
limit, astronomers photographed the close companion to Polaris, known 
also as the North Star, for the first time. 

"Hubble's exceptional pointing capabilities combined with the 
wonderful performance of its instruments allow scientists to see the 
universe in finer detail than ever before," said Michael Moore, 
NASA's Hubble program executive. "It is that clear vision that makes 
these types of images possible," he added. 

The North Star is thought to be a steady, solitary point of light that 
guided sailors for ages, but there is more to this star than meets 
the eye. The North Star is actually a triple star system. While one 
companion is easily viewed with small telescopes, the other hugs 
Polaris so tightly that it has never been seen until now. 

"The star we observed is so close to Polaris that we needed every 
available bit of Hubble's resolution to see it," said astronomer 
Nancy Evans of the Harvard-Smithsonian Center for Astrophysics, 
Cambridge, Mass. The companion proved to be less than two-tenths of 
an arcsecond from Polaris. That is an incredibly tiny angle 
equivalent to the apparent diameter of a quarter located 19 miles 
away. At the system's distance of 430 light-years from Earth, that 
translates into a separation of about 2 billion miles. 

"The brightness difference between the two stars made it even more 
difficult to resolve them," said astronomer Howard Bond of the Space 
Telescope Science Institute, Baltimore. Polaris is a super-giant more 
than two thousand times brighter than the sun, while its companion is 
a dwarf star. "With Hubble, we've pulled the North Star's companion 
out of the shadows and into the spotlight," he said. 

"Our ultimate goal is to get the accurate mass for Polaris," Evans 
said. "To do that, the next milestone is to measure the motion of the 
companion in its orbit," she added. Astronomers want to determine the 
mass of Polaris, because it is the nearest Cepheid variable star. 
Cepheids' brightness variations are used to measure the distances of 
galaxies and the expansion rate of the universe. It is essential to 
understand their intrinsic physics makeup and evolution. Knowing 
their mass is the most important ingredient in this understanding. 

The researchers plan to continue observing the Polaris system for 
several years. The movement of the small companion during its 30-year 
orbit around the primary should be detectable. The researchers 
presented their data today during the 207th meeting of the American 
Astronomical Society in Washington. 

The Hubble Space Telescope is a project of international cooperation 
between NASA and the European Space Agency. The Space Telescope 
Science Institute in Baltimore conducts Hubble science operations. 
The Institute is operated for NASA by the Association of Universities 
for Research in Astronomy, Inc., Washington. 

For images and additional information about this research on the Web, 
visit: 

http://hubblesite.org/news/2006/02

For information about NASA and agency programs on the Web, visit: 

http://www.nasa.gov/home 

	
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