Brian Jones: Triangulum
During December evenings, the tiny constellation Triangulum can be seen virtually overhead, located immediately to the south of a line between Mirach and Alamak in the neighbouring Andromeda as shown here. Triangulum is unusual in that it’s one of the few constellations that actually resembles the object that it is supposed to depict, its three main stars forming a small, elongated triangle which, once spotted, is unmistakeable. The constellation includes its three main stars along with the fainter Delta and 7 which both lie close to Gamma and which form a pretty little group when viewed through binoculars.
Alternative names for this tiny constellation include Delta, or Deltaton, by which it was known to Greek and Roman astronomers due to the resemblance of the constellation to the Greek capital letter Delta (Δ) leading also to ‘Home of the Nile’ or ‘Gift of the Nile’, which names reflected the general shape with that of the Nile Delta. The Latin author Hyginus recorded that the group was considered by some astronomers to have a shape not unlike that of the island of Sicily, home of Ceres, the goddess of agriculture and an island originally known as Trinacria due to its three promontories.
Alpha, along with Beta, were known as Al Mizan, the Scale-beam, to Arabic astronomers.
Triangulum plays host to the spiral galaxy M33, also know as the Triangulum Spiral galaxy or Pinwheel Galaxy. Discovered by the French astronomer Charles Messier in 1764, this object is a member of what is known as the Local Group, a collection of galaxies of which our own Milky Way galaxy is also a member (as is the Andromeda Spiral galaxy featured in last month’s blog). Lying at a distance of around 2.4 million light years, M33 has a tiny nucleus and huge sweeping spiral arms.
M33 has a very low surface brightness and is easily blotted out by moonlight. However, if the sky is really dark and clear, and you have a good pair of binoculars, you may be able to locate the galaxy by following the line of stars from Alpha as shown on the accompanying finder chart. The rule is to look for a faint and extensive patch of light rather than a more concentrated light source. If you can mount your binoculars on a camera tripod that will help in picking out objects such as the Triangulum Spiral.
While you’re looking at Triangulum, check out the much-smaller triangle of fainter stars located just to the southeast of the group. This is Triangulum Minor and was introduced to star charts by the Polish astronomer Johannes Hevelius in 1687. This tiny triangle of faint stars is no longer recognised as an individual constellation on modern star charts.
Take a trip to check out what this tiny constellation has to offer and to search for the elusive Triangulum Spiral galaxy! Happy stargazing!