Sky and Telescope - May 2012 - (Page 12)

News Notes
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Vast New Trove of Variable Stars
13.8 14.0

Algol type

14.2 14.4 14.6 14.8

W Ursae Majoris type
13.6

13.8 14.0 14.2 14.4

14.6 14.8

RR Lyrae type

Magnitude

15.0 15.2 15.4 15.6 15.8 0.0 0.5 1.0 1.5 2.0

Phase These light curves of faint variable stars were plucked from the tens of thousands now online courtesy of the Catalina sky surveys. The thin vertical lines are the error bars for each brightness measurement. Algol stars are eclipsing binaries in which the two stars are separated; W Ursae Majoris stars are contact binaries resembling ﬁgure 8s; RR Lyraes are pulsators. These three variables have periods of 0.536934, 0.74429, and 0.331798 days, respectively.
S&T: LEAH TISCIONE, SOURCE: CATALINA SKY SURVEY / ANDREW DRAKE

We live in a golden age of automated sky surveys, and it’s getting more golden all the time. One way that massive sky surveys are changing astronomy is by producing gigantic numbers of uniform, high-quality light curves for new variable stars. Usually these are merely the byproducts of surveys designed for other purposes. But when some project measures the brightnesses of millions of stars over and over, why not save the data and mine it? The largest such variable-star database yet has been compiled by the Catalina Sky Survey and the Catalina Real-Time Transient Survey. Their main jobs are looking for near-Earth asteroids and watching for transient events among the stars and galaxies. But along the way they have collected 20 billion brightness measurements of 198 million stars and other objects since 2004. That’s an average of 100 magnitude measurements for each one. The objects range from magnitude 12.5 to 20 and span a little more than half the celestial sphere. The new light curves include more than 1,000 distant supernovae, some of unusual or new varieties; about 3,000 other transient objects including ﬂare stars, dwarf novae, and erupting galactic nuclei; and tens of thousands of other new variable stars of every kind. By comparison, the oﬃcial General Catalog of Variable Stars, the bible of the ﬁeld since 1948, contains 43,675 named variables. The Catalina light curves are uniform and consistent, with measurements typically accurate to 0.06 or 0.08 magnitude. “This set is an order of magnitude larger than the largest previously available data sets of the kind,” says Andrew Drake (Caltech) of the Catalina project. He also notes, “We discover transient events and publish them electronically in real time, so that anyone can follow them and make additional discoveries.” In this way the program is a precursor to the much bigger Large Synoptic Survey Telescope (LSST) project, which should begin watching the sky with a unique, wide-ﬁeld 8.4-meter scope around the end of this decade. The LSST’s capabilities will be mind-boggling: it’s designed to measure everything across half the celestial sphere from magnitude 16 to 24.5 in six colors an average of once every three or four days for at least 10 years. Catalina’s observations so far come from the Univer-

12 May 2012 sky & telescope

Magnitude

Table of Contents for the Digital Edition of Sky and Telescope - May 2012

Sky and Telescope - May 2012
Table of Contents
Spectrum
Letters
75, 50 & 25 Years Ago
News Notes
Saturn’s Raging Superstorm
Stars Above, Earth Below: Astronomy in National Parks
The Remarkable Case of Comet Lovejoy
In This Section
May’s Sky at a Glance
Binocular Highlight
Planetary Almanac
Northern Hemisphere’s Sky
Sun, Moon, and Planets
Celestial Calendar
Exploring the Solar System
Deep-Sky Wonders
Going Deep
S&T Test Report
New Product Showcase
Telescope Workshop
Planetary Imaging with Your DSLR Camera
Gallery
Focal Point

Sky and Telescope - May 2012