A Close, Quick, and Beautiful Double Star
Posted by Brian Ventrudo
Astronomers best know the sprawling constellation Virgo for its rich trove of distant galaxies. But Virgo holds a much closer object, the fine binary star Porrima, one of the few stars close enough to show detectable motion during the brief span of a human lifetime. Here’s how to see this fine double star…
Porrima lies at the southern end of a large arc of stars which starts at Vindemiatrix, then swoops south to delta Virginis, then Porrima itself, then to Zaniah and Zavijava (see map below). This arc of stars represents the “arms of the maiden” Virgo.
Also known as gamma Virginis, Porrima is a lovely double star and at just 39 light years away, a nearby neighbour of our solar system.
Location of the double star Porrima (gamma Virginis). Click to enlarge.
The two stars in this system revolve about each other in 169 years, which means you can see, in a good backyard telescope, the motion of the stars over the course of only a decade or so. Until 1995, a small scope easily split this pair. From 1996 through 2010, the two stars moved too close together to resolve in a small telescope. But by 2010, they separated enough to once again split in a telescope on nights of very steady seeing.
To split Porrima, which is split now by about 1.7″, pick a night when the air is steady and the stars twinkle very little. You’ll need a 3″ or 4″ telescope or larger and a magnification of 200x. Each star in the Porrima system is about magnitude 3.6, and each is a white F-type main sequence star just a little bigger and brighter and hotter than our Sun.
Nestled within the arms of the maiden just north of Porrima are hundreds of galaxies belonging to the Virgo Cluster, the closest major galaxy cluster to Earth. Dozens of these galaxies are visible with a small telescope, including the famous “Markarian’s Chain”, a graceful arc of seven interacting galaxies visible in a small telescope. To tour the Virgo Cluster for yourself, look to the latest deep-sky guide from One-Minute Astronomer. Click here to learn more…
