Astronomy is full of superlatives. Farthest, closest, hottest, densest, biggest, smallest. It’s fun to prowl around the sky in search of these extremes.
Two nights ago, I found myself star-hopping across Canis Major the Greater Dog in search of this or that gas cloud and spotted the star VY Canis Majoris on my atlas. The use of the lettered name “VY” tells us first off that this is a variable star whose light is not constant like the sun’s.
A quick check on the American Association of Variable Star Observers (AAVSO) website shows that VY varies between magnitudes 7.4 at brightest to 9.6. For the past few months it’s been around 8.0, bright enough to see in ordinary binoculars.
But its variability is not exactly the reason I wanted to acquaint you with this star. VY is special for an entirely different reason – it’s the largest star known! Astronomers estimate its diameter at some 2,000 times the size of the sun. And since the sun is no slouch at 864,000 miles across, VY is truly a monster.
Put in place of the sun at the center of the solar system, it would puff out beyond the orbit of Saturn. If the sun were reduced to the size of one of those big rubber balls people use as chairs these days, VY would be a much bigger ball 1.4 miles across. Yet another way to think of its vast girth is to compare how long it would take jet airliner traveling at 550 mph to fly across Earth, sun and VY:
* 14.5 hours non-stop to fly across Earth’s diameter of 8,000 miles
* 65.5 days to cross the sun
* 394 years to complete the 1.9 billion mile flight across VY
Thinking about that makes me want to stand up right now and stretch my legs.
VY is about 5,000 light years from Earth and classified as a red hypergiant star with a temperature of some 5000 degrees F. Surrounding the star is a small nebula of dust and gases VY has expelled in fits and starts during its evolution from a white supergiant star to its present state. Really big stars like VY eventually run of off nuclear fuel in their cores, collapse under the pull of gravity and then explode as supernovas. VY is so enormous that scientists predict it will one day become a powerful hypernova – ah, yet another superlative! – and might even collapse to form a black hole.
You have plenty of time to see this magnificent star before that happens. First, shoot a line through the belt of Orion towards the east until you come to Sirius. An outstretched fist below Sirius, find a triangle of three easy-to-see stars, then use the detailed map (above) to star-hop your way to VY just as I did. For reference, the “triangle” fits nicely in a the field of view of typical binoculars.
Those with telescopes are in for a treat. If the air is steady and you study VY closely at medium and higher magnifications, you’ll see a very small red-colored nebula around the star.This is material that’s been expelled during the star’s outbursts.
I’ve also included two other “must-sees” on the map — the beautiful, colorful double star h3945 which any scope can split into two and the stunning little cluster surrounding Tau called NGC 2362. See them all and you’ll have a most satisfying night.