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UA sky survey captures hundreds of millions of stars

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UA sky survey captures hundreds of millions of stars

Project offers celestial data for public and professionals

  • Data is collected using the Catalina Schmidt telescope on Mount Bigelow.
    CSS Survey Team/University of ArizonaData is collected using the Catalina Schmidt telescope on Mount Bigelow.
  • A graph shows the brightness history of a dwarf nova over a period of seven years. The pictures at the top correspond to the high and low states, indicated by the arrows.
    CRTS Survey Team/California Institute of TechnologyA graph shows the brightness history of a dwarf nova over a period of seven years. The pictures at the top correspond to the high and low states, indicated by the arrows.

 The drama of exploding stars and changing galaxies has been playing out on through the lenses of scientists' telescopes for years.

But now the images and data for over 200 million celestial bodies — from stars to supernovas — are now available to the public thanks to the work of astronomers from the University of Arizona and the California Institute of Technology.

The Catalina Sky Survey has produced trillions of bytes of information depicting the brightening and dimming of stars since 2004.

The project originally was commissioned by NASA to keep tabs on asteroids that potentially could collide with Earth.

In 2007, colleagues at CalTech who wanted to use UA's data to investigate stationary objects approached the scientists.

"This set of objects is an order of magnitude larger than the largest previously available data sets of their kind," said Andrew Drake, a staff scientist at CalTech, in a press release.

The Catalina Real-Time Transient Survey (CRTS) notes of the objects that change. The quintessential star twinkles, but they also pulsate, or ring like a bell, explained Ed Beshore, the principal investigator of the Catalina Sky Survey.

Technically, a star is a sphere of gas that has ignited in space. The push and pull of gravity and radiation causes its brightness to fluctuate. As a star dies, its usual brightness can change dramatically.

“Some stars fade away with a whimper and some stars explode catastrophically,” Beshore said.

These show-stopping explosions are supernovas.

Sharing the wealth

“There’re no barriers for people to use this data, so it’s open,” Beshore said. “So we invite anybody, both the public and professionals, to come access this data.”

The Catalina Real-Time Transient Survey collects images from 33,000 square degrees of sky from three telescopes. This wide range captures images of other galaxies and their hundreds of millions of stars.

S. George Djorgovski, an astronomy professor at CalTech and principal investigator on CRTS, said the program is a good example of data sharing.

"We hope to set an example of how data-intensive science should be done in the 21st century," Djorgovski said in a press release.

The information is invaluable to observers who believe they have stumbled upon an object out of the ordinary. 

“If you met somebody on the street and they were kind of odd in behavior, you might go to one of your friends and ask ‘Has this guy ever done this before?’ ” Beshore said.

Observers can compare “odd” star behavior with the information in the database using celestial coordinates, which are comparable to the longitude and latitude of a body in space.  Observers also can search stars by name.

Prospective astronomers can view the brightness history of the star and download the information.

The historical data can help indicate whether additional funds and time should be allocated toward a potential “new and exciting object.”

“Astronomers have a whole arsenal of instruments they can use to study the heavens, but some of those instruments are very expensive,” Beshore said.

The program receives about $300,00 annually from the National Science Foundation, Drake said.

If their grant is renewed, they hope to add the information from telescopes on Mount Lemmon and in Australia to the database in the coming months, he said.

Technology doesn’t do all the work

On roughly 24 clear nights a month, two scientists from the UA Lunar and Planetary Laboratory venture out to the 0.7-meter telescope on the top of Mount Bigelow in the Catalina Mountains.

During the winter, the astronomers begin observing the skies at 5 p.m. and don’t rest until 7 the next morning.

“Scientists very rarely put their eyes to a telescope because the eye is a relatively poor sensor of light compared to the devices we use now,” Beshore explained.

Instead, the sensors of these imaging devices are akin to those found on digital cameras.

“Without computers this would have been totally impossible to manage,” Beshore said.

He recalled that as an undergraduate at the University of Arizona in the 1970s, it could take hours to process a single star image.

Now 450 images are collected from each telescope every night of observation. There are hundreds of thousands of individual star images analyzed, Beshore said.

The computers filter out previously discovered objects and alert scientist to new subjects. Researchers at Cal-Tech then analyze these images.

A human eye can distinguish stray cosmic rays or even planes from objects of real interest. 

“At that point, it goes into a database and a notification of the brightness is transmitted observers around the world,” Beshore said. He likens the notification to Twitter for astronomers.

Historically, astronomy has only studied static images. Now scientists are starting to look at behavior of moving objects over time.

“It would be arrogant for us to think that we have found everything that is really interesting,” Beshore said.

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