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August 2, 2016

The Sun is pretty big as stars go — bigger than perhaps 80 or 90 percent of the stars in our entire galaxy. To get an idea of just how big, consider this: At the speed of a jet airliner, it would take about seven months to circle all the way around the Sun’s equator.

But if you really want to rack up the frequent-flier miles, try circling around the star at the tail of Cygnus, the swan.

Deneb is classified as a white supergiant. The “white” designation means that its surface is thousands of degrees hotter than the Sun’s. And the “supergiant” designation means that it’s one of the biggest stars in the galaxy. In fact, some recent measurements say it could be 200 times the diameter of the Sun. So even at the quick pace of a typical airliner, it would take more than a century to circle Deneb’s equator.

One problem you might have is deciding just where the star’s “surface” is. Supergiants are so puffed up that their outermost layers of gas are quite thin. And Deneb is blowing a strong “wind” of material out into space, which makes it even harder to tell where the star ends and space begins.

But from our distance of perhaps 2500 light-years or so, that’s not a problem — Deneb looks like a sharp little point of light. It’s high in the east-northeast at nightfall, at the left point of the bright Summer Triangle. The rest of the swan stretches to its right, with the body parallel to the horizon and the wings spread above and below.


Script by Damond Benningfield

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