Science & history · Asterism guide
The Summer Triangle
The Summer Triangle is three bright stars in three different constellations: Vega in Lyra, Deneb in Cygnus and Altair in Aquila. It is an asterism, and its name is a Northern Hemisphere name.
About this picture
NASA/Goddard Space Flight Center Scientific Visualization Studio. Gaia DR2: ESA/Gaia/DPAC. Constellation figures based on those developed for the IAU by Alan MacRobert of Sky and Telescope magazine (Roger Sinnott and Rick Fienberg). NASA's page (opens in a new tab).
The map is a composite of 1.7 billion catalogued stars, not a photograph from one place: it shows stars far too faint for the eye, and no weather, Moon or city light. It is drawn here in this chart's projection, with each star where it was in 2000; the fastest-moving bright star has shifted about a minute of arc since, far less than a pixel here.
How to spot it: Three bright stars in a big triangle: Vega, Deneb and Altair. Source (opens in a new tab)
Three constellations, one shape
Three bright stars, one from each of three constellations: a pattern, not a group.
NASA (opens in a new tab) describes the Summer Triangle as the three very bright stars Vega, Altair and Deneb, and the IAU (opens in a new tab) uses it as an example of an asterism built from stars of three different constellations: Lyra, Cygnus and Aquila.
Because it belongs to no one constellation, it is one of the familiar patterns (opens in a new tab) people use rather than an official area of sky. Constellations and asterisms explains the difference.
Sources for this section Preston Dyches, What Are Asterisms?, NASA Science (2021, updated 2024) (opens in a new tab); International Astronomical Union, The Constellations (opens in a new tab)
Neighbours only in the sky
The three corners lie at wildly different distances, from 17 to about 1,400 light-years.
The corners are nowhere near each other in space. Altair is 16.8 light-years (opens in a new tab) away and Vega 25.3, while Deneb is about 1,400 (opens in a new tab), the most distant of all first-magnitude stars.
Deneb looks almost as bright as the others only because it is a hugely luminous supergiant. How bright a star looks depends on both its power and its distance, as NASA explains (opens in a new tab); brightness and distance goes further.
Sources for this section ESA, Hipparcos: The 50 Brightest Stars (opens in a new tab); Ian Ridpath, Star Tales: Cygnus (opens in a new tab); NASA Science, Stars in an Exoplanet World (opens in a new tab)
Summer where?
High on northern summer evenings; low in the north on southern winter evenings.
“Summer” is a northern name. NASA (opens in a new tab) notes that the Triangle stands high overhead on summer evenings in the Northern Hemisphere, and the Night Sky Network (opens in a new tab) that Altair, the last corner to rise, is high overhead at sunset by the end of the season in September.
By this site's calculation (opens in a new tab), the Triangle's middle stands about 82° up in the south at its highest from 40°N but about 23° up in the north from 35°S, so from the Southern Hemisphere it is a winter sight low in the north. It is highest at about 9 p.m. local time in mid-September; the computed block gives the latitudes where it rises.
How to see it It shows even in light-polluted city skies (opens in a new tab), so it is a good first pattern to learn: three bright stars in a big, long triangle, with Vega the brightest corner.
Sources for this section Preston Dyches, What Are Asterisms?, NASA Science (2021, updated 2024) (opens in a new tab); Kat Troche (Astronomical Society of the Pacific), Summer Triangle Corner: Altair, NASA Night Sky Network (opens in a new tab); Bright Star Catalogue, 5th Revised Ed. (Hoffleit & Warren 1991), as computed by this site's star engine (opens in a new tab)
The Milky Way through it
Under a dark sky the Milky Way runs through the Triangle, split by a dark lane.
The Milky Way crosses the Triangle, and the Night Sky Network (opens in a new tab) describes a dark lane, the Great Rift, running from the Summer Triangle down toward Sagittarius: massive clouds of dust between us and the inner Galaxy.
Unlike the three stars, the Milky Way is faint. Seeing it (opens in a new tab) takes clear, dark skies, eyes adapted to the dark, no bright lights, and a new or crescent Moon; many city dwellers first see it on a trip to the countryside.
Keep in mind Photographs of the Milky Way show far more detail and colour than the eye can (opens in a new tab).
Sources for this section Kat Troche (Astronomical Society of the Pacific), The Great Rift, NASA Night Sky Network (2025) (opens in a new tab)
Where on Earth, and when
The whole key pattern rises from anywhere north of about 45°S.
South of about 81°S, none of it rises.
North of about 81°N, the whole key pattern never sets.
Its middle climbs at least 20° high, the finder's threshold for a suggestion, from anywhere north of about 38°S.
It is highest in the evening sky, at about 9 p.m. local time, in mid-September, from either hemisphere, wherever it rises. With daylight saving time, that is nearer 10 p.m. on the clock.
Worked out by this site from the Bright Star Catalogue, for a flat, clear horizon. Hills, buildings, haze and city light all cut into this; the air also lifts objects near the horizon by about half a degree. For your own place and night, use the sky finder.
Sources
- Astronomy Preston Dyches, What Are Asterisms?, NASA Science (2021, updated 2024) (opens in a new tab) for the three stars, city skies and northern summer evenings · checked 27 September 2026
- Astronomy International Astronomical Union, The Constellations (opens in a new tab) for an asterism from three constellations · checked 27 September 2026
- Astronomy ESA, Hipparcos: The 50 Brightest Stars (opens in a new tab) for the distances of Vega and Altair · checked 27 September 2026
- History Ian Ridpath, Star Tales: Cygnus (opens in a new tab) for Deneb's distance · checked 27 September 2026
- Astronomy NASA Science, Stars in an Exoplanet World (opens in a new tab) for brightness and distance · checked 27 September 2026
- Astronomy Kat Troche (Astronomical Society of the Pacific), Summer Triangle Corner: Altair, NASA Night Sky Network (opens in a new tab) for Altair rising last · checked 27 September 2026
- Astronomy Kat Troche (Astronomical Society of the Pacific), The Great Rift, NASA Night Sky Network (2025) (opens in a new tab) for the Milky Way and the Great Rift · checked 27 September 2026
- Astronomy Bright Star Catalogue, 5th Revised Ed. (Hoffleit & Warren 1991), as computed by this site's star engine (opens in a new tab) for its height from 40°N and 35°S, and best month
