Constellation · Triangulum · Tri

Triangulum constellation: how to find it, when to see it and what is in it

northernbest in december1 bright star

In short

Triangulum (Tri) is a northern constellation covering 132 square degrees, number 78 of 88 by size. Its brightest star is Alaybasan, a white giant, magnitude 3.0. It is best seen in the evening in December. Over London it rises and sets and is well placed in its season. Its neighbours in the sky: Andromeda, Aries, Perseus, Pisces.

Area: 132 square degrees, 78 of 88 · Neighbours: Andromeda, Aries, Perseus, Pisces · Updated 10 October 2026

How to find Triangulum

1
When to look
The best time is in December in the evening: in the south, around 20:29.
2
Use the neighbours
Find it from the neighbouring constellations: Andromeda, Aries, Perseus, Pisces.
3
Brightest stars
The brightest stars of the figure: Alaybasan (3.0ᵐ), Mothallah (3.4ᵐ), Apdu (4.0ᵐ).

When it is visible over London

Month	Where and when	Conditions
January	in the south, around 18:26	in the evening
February	in the southwest, around 18:29	in the evening
March	in the west, around 19:17	in the evening
April	in the northwest, around 21:16	low, needs an open horizon
May	—	not visible, behind the Sun
June	in the northeast, around 02:36	low, needs an open horizon
July	in the east, around 03:00	before dawn
August	in the southeast, around 04:18	before dawn
September	in the south, around 03:28	before dawn
October — november	in the south, around 01:34	around midnight
December	in the south, around 20:29	in the evening