Triangulum
Triangulum, a slender triangle formed by three stars. It hides the spiral galaxy M33, one of the farthest objects visible to the naked eye.
Science
The scienceTriangulum is a small constellation whose three stars form a slender, elongated isosceles triangle, and thanks to that simple, distinct shape it has been recognized as a constellation since ancient times. It has no bright stars, yet within it hides a treasure — the "Triangulum Galaxy" (M33). This spiral galaxy is counted, along with the Andromeda Galaxy and our own Milky Way, among the three principal galaxies of the "Local Group"; lying about 2.7 million light-years away, it is very faint, and under exceptionally dark, clear skies it is often taken up as a challenge, one of the farthest objects visible to the naked eye.
Mythology
How it became a constellationTriangulum resembles delta (Δ), the fourth letter of the Greek alphabet, and so the ancient Greeks called it "Deltoton." Rather than the hero of any clear myth, it was thought to represent the delta of the Nile or the triangular outline of the island of Sicily. Because Demeter (Ceres), goddess of grain, held Sicily especially dear, one tale says the goddess asked Zeus to set a triangle modeled on the island in the sky. Small but ancient and distinct, it is the constellation of geometry.
Observing Guide
how to observe🔭 How to find it
On autumn evenings, look south of Mirach (the bright star of Andromeda), beside Aries, for a slender, elongated isosceles triangle of three stars. There are no bright stars, but the three form a clear triangle that's simple and easy to recognize, and it lies right along the path leading down from the Great Square of Pegasus through Andromeda, so its position is easy to pin down.
✨ What to look for
Small as it is, Triangulum hides a great treasure: the "Triangulum Galaxy," M33. Along with the Andromeda Galaxy and our own Milky Way, it's one of the three great spiral galaxies of the Local Group. At about 2.7 million light-years away, it's a target for attempting the most distant object visible to the naked eye under a very clear, dark sky. Its surface brightness is low and it spreads out so broadly that binoculars can actually serve better than a telescope.
📍 Where to see it (US · Canada · UK · Australia)
With its stars around +29° to +35°, Triangulum is well placed for the US, Canada, and the UK, riding high in the southern sky on autumn evenings (September–December); a dark, transparent night is essential to glimpse the galaxy M33. From Australia the little triangle appears low in the northern sky during the southern spring, so northern observers enjoy the better view.