Triangulum and Aries

by | Jan 1, 2023 | 0 comments

Triangulum and Aries are a pair of small constellations that lie south of Andromeda, between the Great Square of Pegasus and the Pleiades. Triangulum, the Triangle, is the more northerly of the pair, lying just south of the eastern part of Andromeda. This unimaginatively named constellation is shaped like a thin isosceles triangle. Aries, the Ram, consists of a simple curved line of four stars sitting just south of Triangulum.

Triangulum is best known for its brightest galaxy, a spiral called M33 (also known as the Triangulum Galaxy). This galaxy is one of the Milky Way’s nearest neighbors, lying approximately 3 million light-years away. M33 lies just over 4° west of Mothallah, the star at the southwestern tip of Triangulum.

M33 is oriented nearly face-on to the Milky Way, which allows us to see its spiral structure. However, this orientation also spreads the light of the galaxy over a greater area. As a result, M33 is a large low-contrast object; in astronomers’ terms, it has a low surface brightness. This galaxy can be relatively easy to observe with low magnification in clear, dark skies; many stargazers have even glimpsed it with the unaided eye in a dark sky. However, M33 is far more difficult to see if the sky is hazy or brightened by moonlight or light pollution.

Due to its large size, M33 is at least as easy to spot with binoculars as it is with a telescope. However, ordinary binoculars will not show detail within the galaxy, though they will readily reveal its oblong glow. Telescopes give the best views of M33; just be sure to use low magnification, especially to find the galaxy. An 8”–10” telescope under good skies should show the major spiral arms of M33, although this structure will be much less obvious than in photographs. Along with the spiral structure, look for the emission nebulas that dot the arms of M33. Several nebulas are visible with larger telescopes as small knots of light that are slightly brighter than the surrounding parts of the galaxy. The brightest of these nebulas, NGC 604, is visible in any good mid-sized telescope.

Aries contains a few faint galaxies, but its most interesting telescopic targets are its double stars. One of these doubles, named Mesarthim, is the star at the southwest end of the constellation figure. Mesarthim is a perfectly matched pair of white stars separated by about 7.5 arcseconds—just wide enough to separate at low to moderate magnifications (try 50–80×).

A dimmer double star called Struve 326 lies on the opposite side of Aries from Mesarthim, just over 1° east of the star 41 Arietis. Struve 326 is a little too dim to be visible with the unaided eye, but it is easy to see with optical aid. The brighter component star is yellow-orange, while the dimmer component is a deeper orange or reddish color. This double is slightly tighter than Mesarthim, so you’ll probably need to use a little more magnification to split this one.

star map of Triangulum and Aries

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