Summer Triangle: 3 Stars From 3 Constellations
The Summer Triangle is a prominent star pattern. Its stars (Vega, Deneb, Altair) are so bright that the pattern is visible even on bright summer evenings in the Northern Hemisphere. But don't let the name fool you — although it's called the "Summer" Triangle, it's actually visible all year round! Use the Sky Tonight app to easily find the Summer Triangle tonight. Read on to learn all the interesting things about this star pattern.
Contents
- Summer Triangle stars
- How to see the Summer Triangle
- When can you see the Summer Triangle
- Is the Summer Triangle a constellation?
- Constellations that form the Summer Triangle
- Constellations inside the Summer Triangle
- The Summer Triangle and Milky Way
- Deep-sky objects inside the Summer Triangle
- The first mention of the Summer Triangle
- The Summer Triangle: bottom line
Summer Triangle stars
The Summer Triangle is an asterism visible all year round (at least partially) from the Northern Hemisphere. The best season for spotting it is the warm summer when it rises the highest in the sky. No surprise that it is one of the most famous asterisms in the sky! The Summer Triangle is also large; it’s formed by the brightest stars from three constellations. These stars (from brightest to dimmest) are:
- Vega (α Lyrae, HIP 91262) in Lyra (the Harp);
- Altair (α Aquilae, HIP 97649) in Aquila (the Eagle);
- Deneb (α Cygni, HIP 102098) in Cygnus (the Swan).
How to see the Summer Triangle
The size of the Summer Triangle is its distinguishing feature. Once you understand the scale of this star pattern, it becomes easy to identify.
On any summer night in the Northern Hemisphere, look east to see blue-white Vega (mag 0.03) — the brightest star in Lyra and the Summer Triangle and the third-brightest star in the Northern Hemisphere (after Sirius and Arcturus). It’s so bright that it can even be visible from light-polluted cities! To make sure that you’re looking at Vega and not some other star, use the mobile sky map (like Sky Tonight) and identify the star.
From Vega, look down to the left — 24 degrees away is Deneb (mag 1.25) in Cygnus. To measure degrees without special tools, stretch out your arm and make a fist. A clenched fist measures about 10 degrees.
To the lower right of Vega is Altair (mag 0.77), the brightest star in Aquila. The distance between them is 34 degrees (one clenched fist more than from Vega to Deneb).
That’s it! Connect these three dots, and you’ll get the Summer Triangle. To check if you identified it correctly, open the Sky Tonight app and go to the search window. Start typing the “Summer Triangle” in the search bar, and once the corresponding result appears, tap the blue target icon next to it. The app will show you the Summer Triangle’s location in your sky. Point your device at the sky — the app will show you the live star map and track your movements.
When can you see the Summer Triangle
The Summer Triangle can be seen at any time of the year, but it rises the highest in the sky during summer in the Northern Hemisphere. From June, the three bright stars appear in the eastern sky and travel across the night sky all night long.
In the late northern autumn and winter, the position of Vega, Deneb, and Altair changes. They start to appear high above the western horizon, while the southernmost Altair sets by about 22:00 local time. In spring, the asterism is again visible in the east, but during the early morning.
Is the Summer Triangle a constellation?
The Summer Triangle is a famous asterism, not a constellation. The difference, in reality, is only an official recognition: the boundaries of 88 constellations were adopted by the International Astronomical Union in 1928, and the rest of the known star patterns became asterisms. By definition, an asterism is a well-known star pattern that can fit into a single constellation (like the Big Dipper, a part of the Ursa Major) or span across several ones. This is the case with the Summer Triangle — its endpoints lie in three constellations, Lyra, Cygnus, and Aquila. But inside of this asterism lie two more — Sagitta and Vulpecula. So in total, it spans across five constellations!
Constellations that form the Summer Triangle
Vega (constellation Lyra)
Can you see the four fainter stars forming a small parallelogram just below Vega? This shape is the body of the musical harp that makes up the constellation of Lyra. Vega marks the top of the instrument’s neck.
Vega’s visual magnitude, or brightness, is the zero reference point for the scale we use to define stars’ brightness values. Objects brighter than Vega have values lower than zero, and vice versa. For example, Antares, the bright, reddish star sitting over the southern horizon in Scorpius, has a value of about 1.0, making it 2.5 times dimmer than Vega. (It’s a logarithmic scale.)
Deneb (constellation Cygnus)
The bright star Deneb marks the tail of the great Cygnus. A faint star about two fist diameters (22°) to its right, in the middle of the Summer Triangle, is Albireo, a colorful double star that marks the swan’s head. If you are in a dark location, you should also be able to see that the Milky Way runs right through Cygnus, as if the swan is about to land for a swim on that celestial river!
Altair (constellation Aquila)
The most southerly of the triangle’s corners is marked by Altair – the head of the great eagle Aquila. At only 16.8 light-years away, Altair is one of the nearest bright stars – so close that its surface has been imaged! The star also seems to be spinning 100 times faster than our Sun.
Constellations inside the Summer Triangle
Sagitta
Sagitta comprises five faint stars, aligned left to right, located midway between Altair and Albireo. The three stars on the constellation's right end form the feathers.
Vulpecula
There’s one more small constellation inside the Summer Triangle, but its dim stars make it difficult to see from the city. It’s called Vulpecula. It is made up of only two magnitude 4.5 stars and is located north of Sagitta, near Albireo.
The Summer Triangle and Milky Way
Did you know that the Summer Triangle can help you find the Milky Way galaxy? The Milky Way is located between Vega and Altair, with Deneb in the middle of this river of stars. The problem is actually seeing the Milky Way. In fact, due to the light pollution, the Milky Way is hidden from more than a third of humanity, including 60% of Europeans and nearly 80% of North Americans.
To view the galaxy, you'll need a clear sky with no clouds, Moon, or city lights — the darker the sky, the better your chances of seeing it. We’ll have a better view of the galaxy starting in August.
Deep-sky objects inside the Summer Triangle
Once you have mastered the Summer Triangle, you can level up your observations and search for more difficult objects within it. Grab your binoculars and look about midway between Vega and Altair for a little grouping of stars called the Coathanger. It’s composed of a rod made of a line of six stars plus a hook made up of four stars. (Hint: For North American observers, it’s oriented with the hook downwards to the right.) Its fancier names include Brocchi’s Cluster, Al Sufi’s Cluster, and Collinder 399.
In the constellation Sagitta, near the bright Altair, there's a fairly bright globular star cluster named Messier 71 or the Angelfish Cluster. Under a dark sky, binoculars should show it as a small, faint, fuzzy star. In a backyard telescope, it will resemble a mound of sugar sprinkled on black velvet.
One of Vulpecula’s claims to fame is the spectacular planetary nebula known as the Dumbbell, also known as the Apple Core Nebula, Messier 27, NGC 6853. From a dark location, aim your telescope 3° to the celestial north-northwest of Sagitta’s arrow tip and look for a small, faintly glowing cloud of gas that resembles an apple core.
Learn more about the space objects visible in the Summer Triangle asterism from Chris Vaughan's (aka Astrogeoguy) Skylights.
The first mention of the Summer Triangle
The earliest “official” mention of the Summer Triangle dates back to 1839, according to Sky & Telescope. The asterism’s name itself was popularized in the 1950s by the British astronomer Sir Patrick Moore and American author H.A. Rey. By the way, it was also called the Navigator's Triangle because military navigators used it for orientation before GPS and other navigation devices were invented.
The Summer Triangle: bottom line
The Summer Triangle is an asterism that shines nearly overhead in the evening sky during summer nights in the Northern Hemisphere. It’s formed by the bright stars Deneb, Vega, and Altair from three different constellations and also crosses two smaller constellations. The Summer Triangle is huge: from Vega to Altair, it measures 34 degrees, or about one-fifth of the sky's dome! The easiest way to find this prominent star pattern in the sky is to use the Sky Tonight astronomy app.
