In this article, we’ll be sharing with you everything you need to know about the constellation of Triangulum, including how to find it, deep space objects contained within it and how to use it to find other night sky objects more easily.

The Constellation of Triangulum 

This constellation was known to several ancient cultures and they all associated its shape with triangular objects.

To the ancient Egyptians, it represented the Nile River delta. Ancient Babylonians knew it and Gamma Andromedae as the plough. Ancient Romans called it ‘Sicilia’ due to its resemblance to the island of Sicily.

Triangulum is one of the constellations that Greek astronomer Ptolemy cataloged over 2000 years ago. The Greeks knew this constellation as ‘Deltoton’ as its shape resembled the capital Greek letter ‘delta’. ‘Triangulum’ is Latin for ‘the triangle’ and there are no myths associated with this constellation. 

To help you spot Triangulum, here’s what SkySafari 6 shows.

Triangulum as shown by SkySafari
Triangulum as shown by SkySafari. Click for full-screen.

Triangulum has an area of 132 square degrees making it the 78th largest of the 88 recognized constellations. Triangulum’s brightest stars (Alpha Trianguli, Beta Trianguli and Gamma Trianguli) form the shape of a nearly perfect isosceles triangle.

The boundary and neighboring constellations for Triangulum.
The boundary and neighboring constellations for Triangulum. Click for full-screen.

In the next section, we’ll show you how to discover Triangulum for yourself.

How To Find Triangulum In The Night Sky

Triangulum is part of the Perseus family of constellations and is visible to observers at latitudes between +90° and -60°. Northern Hemisphere observers can see it in the fall and winter, while Southern Hemisphere observers can see it in the spring and summer. The constellation of Triangulum is bordered by Andromeda, Aries, Perseus and Pisces

Triangulum at 9 p.m. in mid-December
Triangulum at 9 p.m. in mid-December. Click for full-screen.

To find Triangulum, do a naked-eye search for The Great Square of Pegasus. Draw an imaginary line from Scheat to Alpheratz (~14°) then extend this line ~22° to Alpha Trianguli. You can measure these distances with your hand at arm’s length.

To find Triangulum’s exact position for your location on any night, use software such as Stellarium (free) or SkySafari.

Triangulum’s Brightest Stars 

Being such a small constellation, it should come as no surprise that Triangulum contains only a few bright stars. Below, we’ve detailed the six that shine around magnitude 5 and brighter.

The brightest stars of Triangulum
The brightest stars of Triangulum. Click for full-screen.

Alpha Trianguli (Metallah, Ras al Mothallath, Caput Trianguli) – This variable double star is the second brightest star in Triangulum and is located at the southwestern apex of the triangle. The magnitude 3.42, yellow-white subgiant primary and magnitude 13.27, secondary components are 100.2 arcseconds apart. Metallah is a rotating variable ranging in magnitude from 3.52 to 3.53. It’s 64 light-years away. ‘Metallah’ and ‘Mothallah’ mean ‘the triangle’ in Arabic. ‘Caput Trianguli’ is Latin for ‘head of the triangle’. 

Beta Trianguli – This variable double star is the brightest in Triangulum and marks the western apex of the triangle. The magnitude 3.01, white, subgiant, primary and secondary components are too close together to be split by a backyard telescope. Beta Trianguli is 124 light-years away. 

Gamma Trianguli – This double star is the third brightest star in Triangulum and marks the eastern apex of the triangle. The magnitude 4.01, white, main sequence, primary and magnitude 19.00, secondary component are 4.7 arcseconds apart. Gamma Trianguli is 118 light-years away.

Delta Trianguli – This double star is the fourth brightest star in Triangulum. The magnitude 4.86, yellow, main sequence, primary and magnitude 13.60, secondary stars are 166.8 arcseconds apart. Delta Trianguli is 35 light-years away. This may be a multiple system. 

Epsilon Trianguli – This variable double star is 392 light-years away. The magnitude 5.51, white, main sequence, primary and magnitude 11.40, secondary components are 4.2 arcseconds apart. This is an eruptive variable. 

6 Trianguli – This double star is 305 light-years away. The magnitude 5.15, yellow-orange giant, primary and magnitude 6.67, blue, secondary component are 3.7 arcseconds apart. This rotating variable ranges in magnitude from 5.19 to 5.28 over 14.7 days.

The primary and secondary stars are both binary stars, making this a quadruple system. 

Star Hopping From Triangulum

Triangulum is too dim to be a good starting point for star hopping.

Objects To See Within Triangulum 

Triangulum contains one Messier object and no other deep sky objects suitable for small telescope users. 

M33 (NGC 598, Triangulum Galaxy, Pinwheel Galaxy) – This spiral galaxy has a magnitude of 5.79 and an apparent size of 62.1 x 36.7 arcminutes. It’s ~3.0 million light-years away and is at right ascension 01h 33m 51s and declination 30° 39’ 36”.

Summary

Triangulum is a small constellation containing only a few bright stars and one deep sky object for small telescope users. Look for it between Aries and the Great Square of Pegasus this fall and winter. 

Author