Although the bright moon is sure to erase many stars from the slate of night tonight, the three stars of the signpost Summer Triangle are likely to withstand the moonlit glare. Oftentimes, you can see these Summer Triangle stars – Vega, Deneb and Altair – from the downtown region of a light-polluted city.
If you live at middle latitudes in the Northern Hemisphere – like in the U.S. and Europe – look for the humongous Summer Triangle to fill up much of the sky above tonight’s waxing gibbous moon. This evening, the moon sits rather low in the southern sky, while Vega – the Summer Triangle’s brightest star – shines high overhead. Deneb, the faintest of these three bright stars, also shines way high in the sky, to the east of Vega. The Summer Triangle’s southernmost star – Altair – is found roughly midway between the horizon and straight overhead.
You can also see the Summer Triangle from the Southern Hemisphere, except that you’ll see it in the northern sky and “upside down.” From places such as South Africa or Australia, tonight’s moon shines way up high, whereas the Summer Triangle shines beneath it in the northern sky. Altair shines at top whereas Vega and Deneb glimmer way down low, near the northern horizon.
The ecliptic – the sun’s yearly path in front of the backdrop stars – passes through the constellations Sagittarius and Capricornus to the south of the Summer Triangle. When the sun is in front of these constellations, we have winter in the Northern Hemisphere and summer in the Summer Hemisphere. That’s why these two constellations of the Zodiac lodge so low in the Northern Hemisphere sky yet so high in the Southern Hemisphere sky.
Sky chart of the constellation Sagittarius
When the moon drops out of the evening sky in another week or two, use the Summer Triangle to find the constellations Sagittarius and Capricornus in a dark sky. In the meantime, let the brilliant moon help you locate the Summer Triangle, as it swings to the south of this brilliant triangle of stars in late August 2012.