Although the bright moon is sure to erase many stars from the slate of night tonight, the three bright stars of the signpost Summer Triangle asterism 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. So look for tonight’s moon. It may be your guide to the stars of the Summer Triangle. As seen from northerly latitudes, the brilliant Summer Triangle stars Altair, Deneb and Vega appear above the moon on the evenings of August 7, 8 and 9.
Keep in mind that today’s chart covers a lot more area than our charts usually do. As viewed from northerly latitudes, the moon is low in the south, while the stars Vega and Deneb shine high overhead.
If you live at middle latitudes in the Northern Hemisphere – for example, in the U.S. or Europe – look for the humongous Summer Triangle to fill up much of the sky above tonight’s waxing gibbous moon. By mid-to-late evening (roughly 10 p.m. local time or 11 p.m. local daylight-saving time) the moon sits rather low in the southern sky as seen from the northern part of Earth, 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 when contrasted to our northerly perspective. From places such as South Africa or Australia, tonight’s moon shines way up high, while 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 south of the Summer Triangle, through the constellations Sagittarius and Capricornus. 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. You know how the sun travels low in winter, and high in summer? At those times, it’s located in front of these constellations.
Sky chart of the constellation Sagittarius
Bottom line: Let the brilliant moon help you locate the Summer Triangle. The bright waxing gibbous moon swings to the south of this brilliant triangle of stars on August 7, 8 and 9.