Press Release

Astronomers Map 40 Million Stars

By SpaceRef Editor
June 12, 2012
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Astronomers will soon have access to a new map of the sky that accurately measures the brightness and position of over 40 million stars.

This map is a result of the AAVSO Photometric All-Sky Survey, which has completely covered the sky at a level 100 times fainter than any prior stellar catalog. Millions of stars will have their brightness and color measured accurately for the first time in this survey.

“Prior surveys have done a good job measuring the brightness of bright stars. Other organizations have announced plans to measure faint stars. But this goldilocks zone of stars that are neither too bright or too faint has been neglected, until now,” Dr. Arne Henden, Director of the American Association of Variable Star Observers (AAVSO), said.

“This catalog of stars will serve a key link between existing bright catalogs and fainter catalogs planned for the future, such as those created by Pan-STARRS and the LSST observatories,” Dr. Doug Welch, a professor of Physics and Astronomy at McMaster University.

The survey will measure stars ranging from magnitude 10 to 16.5. This is typically the range of stellar brightness that amateur astronomers can see with backyard telescopes. The faintest stars visible to the unaided eye are about 6th magnitude, and 11th-magnitude stars are only 1/100th as bright as that.

“We estimate nearly all of the stars mapped in this survey will be accurately measured for their first time in their history. Tens of thousands of these stars will likely change in brightness over time and need follow up monitoring by amateur astronomers,” Henden said.

The new catalog will also help save professionals valuable time when using major observatories. “Time available for imaging targets on the largest telescopes will be increased by APASS since calibrated stars will exist on the target images themselves. Different pointings for calibration fields won’t be necessary,” Welch said.

This new map of the stars is being generated by telescopes located at two locations: New Mexico and Chile. Each location has two 8-inch (20cm) telescopes that take images of the sky through five colored filters from very blue through deep-red, and cover up to 1,000 square degrees per night. The use of numerous color filters will make it easier for astronomers to combine APASS data with their own observations of a star. The survey began in 2009 and, while having complete sky coverage now, is expected to be available in final form by 2014. Early data has already been released and is available to the public at

The survey is predominantly a pro-am volunteer effort. A team of professional astronomers is primarily responsible for the photometry while a team of amateur astronomers is helping with the equipment, purchased with support from the Robert Martin Ayers Sciences Fund.

Dr. Arne Henden
American Association of Variable Star Observers
+1 (617) 354-0484, cell: +1 (617) 945-6356

The press release accompanies AAS poster 133.06: “The AAVSO Photometric All-Sky Survey Completes the Sky”. Authors: Arne A. Henden (AAVSO), T. C. Smith (DRO), S. E. Levine (Lowell Observatory), D. Terrell (SwRI).

The AAVSO is a non-profit worldwide scientific and educational organization of amateur and professional astronomers who are interested in stars that change in brightness — variable stars. It was founded in 1911 to coordinate variable star observations for Harvard College Observatory.

SpaceRef staff editor.