Summer Triangle

The signature star pattern of summer climbs high across the sky on July nights. It’s so big that it incorporates stars from three constellations. And it’s so bright that it’s easily visible even from light-polluted cities.

The Summer Triangle is well up in the east and northeast as night falls. It passes directly overhead after midnight.

The stars that outline the triangle are Vega, Deneb, and Altair. Vega is the brightest, and it stands at the top of the triangle in early evening. Deneb marks the left point of the triangle, with Altair to the lower right of the other two.

Altair is the closest member of the triangle -- less than 17 light-years away. It’s bigger and brighter than the Sun, but not amazingly so. And it spins much faster than the Sun does, so it’s much fatter through the equator than through the poles.

Vega is about nine light-years farther than Altair. Since it looks brighter, that means it’s much more impressive. In fact, when you add up all wavelengths of light, it’s almost four times Altair’s brightness, and 40 times the Sun’s. And Vega also has a bulging waistline.

The real stunner of the trio, though, is Deneb. It’s about 20 times heavier than the Sun, 200 times wider, and 200,000 times brighter. So while Deneb looks meeker than the others, that’s an illusion -- caused by its distance of about 2600 light-years -- dozens of times farther than the other members of the beautiful Summer Triangle.

Script by Damond Benningfield