What is an Asterism?

An asterism is a pattern or group of stars that form a recognizable shape in the night sky.

They can include stars from one constellation or span across multiple constellations.

Asterisms are typically smaller and easier to spot than constellations, making them popular targets and helpful reference points for stargazers to locate celestial objects.

Asterism vs Constellation

An asterism is a familiar and easily recognizable star pattern, but doesn’t hold official status in astronomy.

Unlike constellations, asterisms are informal groupings of stars without official designation.

Constellations are formally defined regions of the sky with set boundaries established by the International Astronomical Union (IAU). Despite their unofficial status, asterisms are still widely used by stargazers to navigate the night sky.

Famous Asterisms

There are many well-known asterisms in the night sky that are easy to locate, even from light-polluted areas. Here are some favorites:

The Big Dipper

Probably the most famous asterism, the Big Dipper is part of the larger constellation Ursa Major, also known as the Great Bear. Its distinctive shape looks like a ladle or dipper, making it easy to recognize.

The two stars at the end of the “bowl” of the dipper are known as the ‘pointer stars’ because they point towards Polaris, the North Star.

The Big Dipper asterism

The Summer Triangle

The Summer Triangle is an asterism made up of three bright stars: Vega (in the constellation Lyra), Deneb (in Cygnus), and Altair (in Aquila).

These stars form a large triangle that’s visible in the northern hemisphere throughout summer and fall.

Each star belongs to a different constellation, but they come together to form one of the largest and most noticeable asterisms in the sky.

The Winter Triangle

The Winter Triangle is a prominent asterism visible in the winter sky, made up of three bright stars: Sirius (in Canis Major), Betelgeuse (in Orion), and Procyon (in Canis Minor).

These stars form a large triangle and are easy to spot during clear winter nights.

The Teapot

Found in the constellation Sagittarius, the Teapot asterism is a group of stars that form the shape of, you guessed it —a teapot.

It’s an easy target during the summer months. Sagittarius is located in the direction of the center of the Milky Way, so stargazers often use the Teapot as a guide to locate the densest parts of the galaxy.

The Teapot asterism

Orion’s Belt

Orion’s Belt is one of the most iconic and easiest to find asterisms in the night sky. It consists of three bright stars (Alnitak, Alnilam, and Mintaka) lined up in a nearly straight row in the middle of the constellation. These stars mark Orion’s waist and are often used as a starting point to find other objects in the sky.

Orion’s Belt asterism is shown in the constellation Orion

Asterism and Deep-sky Objects

Asterisms are handy tools for helping you find deep-sky objects, such as nebulae, star clusters, and galaxies.

Since many asterisms are bright and easy to spot, they act as useful guides for locating fainter objects nearby.

Here are a few examples:

The Teapot (Sagittarius): Look just above the spout of the Teapot to find the Lagoon Nebula (M8), Trifid Nebula (M20), and M22, a bright globular cluster.
The Big Dipper (Ursa Major): Extend a line from the two stars at the end of the bowl to find Polaris, but also use the handle to curve your way toward Arcturus, then to Spica, passing near deep sky objects like the Whirlpool Galaxy (M51).
Orion’s Belt (Orion): This three-star asterism in the constellation points directly to the Orion Nebula (M42), one of the brightest and most popular deep sky objects. Follow the line down and left to find Sirius, the brightest star in the sky. Follow it up and right to find Aldebaran and the Pleiades star cluster.

Ashley is an environmental educator, communication professional, and astrophotographer. She has extensive experience writing for diverse audiences to increase public awareness and engagement. Ashley is an active Advocate and Delegate with DarkSky International, helping to protect the nighttime environment from the harmful effects of light pollution through advocacy and outreach.