As soon as the summer Sun dips below the horizon, the sky lights up with countless stars. Amidst this bright scattering, the eye immediately notices a familiar and prominent shape – the Great Summer Triangle. This dependable celestial marker for observers worldwide has one interesting feature: despite its popularity, it is not an official constellation.
What is the Great Summer Triangle?
Image Credit & Copyright: Bob King
In astronomy, there is a term “asterism” (from the ancient Greek asterismos – literally “group of stars”). It is used to describe any noticeable star pattern that is not included in the list of 88 constellations officially recognized by the International Astronomical Union (IAU).
It is important to understand the difference: while a constellation is an area of the sky with clearly defined boundaries, an asterism is just a pattern “drawn” by a few bright stars. Therefore, these stars often have nothing to do with each other-they can belong to different constellations and be scattered in space at gigantic distances.
The Summer Triangle is a perfect example of an asterism, as it consists of the main bodies of three different constellations:
- Vega (Lyra);
- Deneb (Cygnus);
- Altair (Aquila).
As for the origin of the name, everything is simple. “Great” because it occupies a huge area of the celestial sphere. “Summer” because it dominates the sky in the Northern Hemisphere at this time of year. “Triangle” – because if you connect its three stars (peaks) with imaginary lines, you will get a triangle.
By the way, did you know that the well-known Plough is also an asterism? Its seven bright stars are only part of the official constellation Ursa Major.
How to find the Great Summer Triangle
Image Credit & Copyright: A. Fujii
Wait for a clear summer evening and look at the eastern part of the sky, focusing on the east azimuth. Vega, the brightest star in the night sky for this part of the sky, will be dominating the sky. At the height of summer, around midnight, it will be almost at its zenith, so you will recognize it unmistakably by its dazzling white-blue light.
Once you find the Vega, look to the right and below. You will see Altair, the second peak that completes the Triangle.
Finally, look to the left and below Vega to find the third star, Deneb. Although it appears to be the dimmest of the trio, its true luminosity (internal luminosity) is incredibly powerful.
A special sight awaits those who observe far from the city lights. Right through the Triangle, between Vega and Altair, a hazy silver streak stretches – this is a cross-section of the disk of our Milky Way galaxy, which we can see from the inside. The Great Triangle is the best guide to finding it.
Not only summer: a tireless celestial traveler
Image Credit & Copyright: Bob King
Despite its name, the Summer Triangle is visible almost all year round. The fact is that due to the Earth’s rotation, its position in the sky is constantly changing, so you just need to look for it at different times of the day in different seasons.
If you are in the Northern Hemisphere, in the fall, it will be waiting for you high in the southwest right after dark; in the winter, it appears in the west for only an hour or two and quickly sinks below the horizon. And in the spring, it returns, rising in the east after midnight and rising high before dawn, as if it were a harbinger of the warmth to come.
If you are in the Southern Hemisphere, get ready to see everything upside down! There, our Summer Triangle becomes the Winter Triangle, dominating the northern part of the sky in an inverted form.
