Volume XVII, Issue 35 # August 27 - September 2, 2009

Sky Watch

by J. Alex Knoll

It’s All a Matter of Scale

While our sun is the biggest light in our lives, it’s a puny star

It’s easy to get lost in the cosmos gazing at a star-filled sky these late-summer nights. Yet looking at a backdrop of tiny, glowing lights with our feet planted on terra firma, you may not realize just how vast space truly is — and, by extension, how small we are.

The waxing gibbous moon reaches first-quarter Thursday, appearing low in the south at sunset, before 7:45 this week. The red light shining beside the moon’s outer edge is Antares, the lead star in the constellation of Scorpius.

While we see the moon dwarfing Antares, the truth is something altogether different. Located some 500 light years from us, this super-giant burns 10,000 times brighter than our own sun. Astronomers have long known that Antares is far more massive than the sun. But more recent observations with NASA’s orbiting infrared Spitzer Space Telescope have revealed a massive nebula surrounding Antares, making its diameter more than 700 times that of the sun.

In place of our own sun, Antares would engulf our solar system almost to Jupiter. In the to-scale comparison at right, our sun disappears. Yet astronomers continue to find ever larger stars, the biggest today being VY Canis Majoris, a hyper-giant 5,000 light years away and more than 2,000 times the size of our sun.

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