Summer Triangle Complete Guide: How to See It Tonight
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
- Where is the Summer Triangle visible?
- How to find the Summer Triangle?
- When can you see the Summer Triangle?
- Is the Summer Triangle a constellation?
- Stars that form the Summer Triangle and their constellations
- 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
Where is the Summer Triangle visible?
The Summer Triangle is a prominent group of stars called an asterism¹. It's visible year-round from most of the Northern Hemisphere, but the best time to see it clearly is in the summer months, when it rises highest in the night sky. Its brightness and easy visibility have made it one of the most popular star patterns!
In the Southern Hemisphere, this star pattern is also visible, but not everywhere: the northernmost star of the pattern, Deneb, doesn’t rise above the horizon for locations south of about 45° latitude. From southern locations like South Africa, southern Australia, and northern New Zealand, Deneb is visible low on the horizon from May through October.
¹Constellations are the 88 star patterns officially recognized by the International Astronomical Union (IAU) in 1922. Other star patterns are called asterisms.
How to find the Summer Triangle?
Finding the Summer Triangle is quite easy — it’s a large asterism 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).
Now, let’s see how to locate these stars in the sky from both the Northern and Southern Hemispheres.
How to see the Summer Triangle from the Northern Hemisphere?
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.
How to see the Summer Triangle from the Southern Hemisphere?
On a clear winter night, look low above the northern horizon to spot the Summer Triangle. In June, it becomes visible around midnight, and each following month, it rises a bit earlier. The nearest star to the horizon is Deneb (mag 1.25) in Cygnus. To its west — approximately the distance of two clenched fists held at arm’s length — is Vega (mag 0.03), the brightest star in Lyra. Above these two stars is Altair (mag 0.77), the brightest star in Aquila, completing the triangle.
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.
From the Southern Hemisphere, observers can see the entire asterism from about May to October. In May, it rises above the horizon closer around 3 a.m., while in August, it rises from evening until about midnight.
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!
People used to create their own constellations all the time, and some of their depictions are just hilarious. Take a look at weird constellations images from old atlases and try to guess if they are still officially recognized by the astronomical society.
Stars that form the Summer Triangle and their constellations
Vega (constellation Lyra)
- Apparent mag: 0.03
- Absolute mag: 0.58
- Type: A0V
- Distance: 25.05 light years
- Mass: 2.1 times the Sun
- Luminosity: 47 times the Sun
- RA: 18h 36m 56s
- Dec.: 38º 47′ 1″
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)
- Apparent mag: 1.25
- Absolute mag: -8.38
- Type: A2Ia
- Distance: 2,616 light years
- Mass: 19 times the Sun
- Luminosity: 196,000 times the Sun
- RA: 20h 41m 25s
- Dec.: 45° 16′ 49″
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)
- Apparent mag: 0.76
- Absolute mag: 2.22
- Type: A7V
- Distance: 16.73 light years
- Mass: 1.86 times the Sun
- Luminosity: 10.6 times the Sun
- RA: 19h 50m 46s
- Dec.: 08° 52′ 05″
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. It contains no stars brighter than fourth magnitude and is the third smallest of the 88 constellations.
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, moonlight, or city lights — the darker the sky, the better your chances of seeing it. So the short, bright summer nights of the Northern Hemisphere aren’t the best time to view the Milky Way. However, the galactic core, the Milky Way’s brightest and densest part that lies in front of the constellation Sagittarius, is visible all night long in June and July, high above your head.
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.
Want to learn what other deep-sky objects are visible in summertime from the Northern Hemisphere? Here are guides by months:
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 and in the winter months in the Southern 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.
