ERIK MARTIN WILLÈN: What Are Asterisms?

Saturday, January 20, 2024

What Are Asterisms? - UNIVERSE

There are 88 star patterns known as constellations that are recognized by astronomers and the International Astronomical Union. The constellations are, technically, regions the sky is divided into in order to help with identifying where objects are located on the sky. In addition to the star patterns within the constellations, there are a variety of other familiar patterns of stars. These are called asterisms.

Some well-known asterisms include:

· The Big Dipper and the Little Dipper – The Big Dipper is also known as the Plow (or Plough, in the United Kingdom). Its stars are part of the constellation Ursa Major, the Great Bear. The Little Dipper is part of the constellation Ursa Minor, the little bear. These asterisms are located very close to each other in the northern sky, and are generally easy to observe.

· The Summer Triangle – Consisting of the three very bright stars Vega, Altair, and Deneb, the Summer Triangle is visible even in light-polluted urban skies. This asterism appears high overhead on summer evenings in the Northern Hemisphere.

· The Winter Circle – Also known as the Winter Hexagon, it’s a ring of six bright stars that spans a very wide region of the sky. In the Northern Hemisphere, you’ll see it rising in the east early in the evening during the time of long, cold nights, and setting in the west earlier and earlier as the season turns to spring.

· The Winter Triangle – This asterism is formed by the bright stars Sirius, Betelgeuse, and Procyon. It’s also visible during winter in the Northern Hemisphere (in fact, it’s part of the Winter Circle).

· The Teapot – Within the constellation Sagittarius is a fun pattern that looks something like a teapot. It’s best seen under skies without a lot of light pollution.

January’s Night Sky Notes: Connecting the ‘Dots’ with Asterisms

An asterism is a pattern of stars in the night sky, forming shapes that make picking out constellations easy. Cultures throughout history have created these patterns as part of storytelling, honoring ancestors, and timekeeping. Orion’s hourglass is just one of many examples of this, but did you know Orion’s brightest knee is part of another asterism that spans six constellations, weaving together the Winter night sky? Many asterisms feature bright stars that are easily visible to the naked eye. Identify these key stars, and then connect the dots to reveal the shape.

Try looking for these asterisms this season and beyond:

· Winter Circle – this asterism, also known as the Winter Hexagon, makes up a large portion of the Winter sky using stars Rigel, Aldebaran, Capella, Pollux, Procyon, and Sirius as its points. Similarly, the Winter Triangle can be found using Procyon, Sirius, and Betelgeuse as points. Orion’s Belt is also considered an asterism.

· Diamond of Virgo – this springtime asterism consists of the following stars: Arcturus, in the constellation Boötes; Cor Caroli, in Canes Venatici; Denebola in Leo, and Spica in Virgo. Sparkling at the center of this diamond is the bright cluster Coma Berenices, or Bernice’s Hair – an ancient asterism turned constellation!

· Summer Triangle – as the nights warm up, the Summer Triangle dominates the heavens. Comprising the bright stars Vega in Lyra, Deneb in Cygnus, and Altair in Aquila, this prominent asterism is the inspiration behind the cultural festival Tanabata. Also found is Cygnus the Swan, which makes up the Northern Cross asterism.

· Great Square of Pegasus – by Autumn, the Great Square of Pegasus can be seen. This square-shaped asterism takes up a large portion of the sky, and consists of the stars: Scheat, Alpheratz, Markab and Algenib.