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Triangulum the Triangle

Gen: Trianguli
Abb: Tri
Dec: +25.4° to +37.0°
RA: 1h 29m to 2h 48m

Triangulum is not a Zodiac constellation, but it is home to a wonderful galaxy M33, also known as the Pinwheel Galaxy.

To the Greeks it was known as Deltoton, because of its resemblance to the Greek Letter Delta. The Romans called this area of the sky Sicilia, as it reminded them of their island of Sicily. It has also been described as the Nile Delta and as an Isosceles Triangle by many other early civilizations. There is another, smaller, group of three stars to the south of Triangulum that Hevelius tried to separate into another constellation, Triangulum Minor. This constellation was not universally accepted so the IAU dropped it from its official list of constellations in 1920.

Exploring in Triangulum

All of the deep sky objects this month are galaxies, with most being very faint. One object in particular is really worth looking at: NGC 598 (M33).

To start out, use your planisphere to locate the long point of the Triangle, Alpha (a) Tri. Also locate b And: (starting at the Great Square of Pegasus, the eastern corner star is Alpheratz (a And); count it as "one". Moving to the east to the 3rd star along the bottom of Andromeda, this is b And). Roughly halfway between a Tri and b And, you will find M33.

M33 is very large so its light is spread over a very large area, making it much fainter than its listed magnitude of 5.7 would suggest. Once you find it, take your time and look at it. At Peddler Hill, my 10" will make out the arms. It generally appears as a large sweeping "S" with a bright core. This galaxy has undergone a tremendous amount of study. The outer reaches of its four arms are dominated by hot, young, blue stars and over 80 HII emission nebulae. On the northeast edge, the largest nebula is NGC604. Several of the others also have NGC numbers but they are not listed in my books. Try using an OIII Filter to bring out these regions.

Return to Alpha Tri and travel a little over 2 degrees northeast; there are two 6th magnitude stars to point the way to NGC777, an E2 galaxy at magnitude 11.4. NGC777 is a large, round appearing galaxy in pair with a much fainter galaxy NGC778.

Continue moving northeast toward Beta Tri (the brightest star in the triangle). About 2/3 of the way from Alpha to Beta you will find Epsilon Tri. Epsilon is an Open Double with its companion located 129 arc sec away to the northwest. From Epsilon hop 1 degree west to NGC750 and NGC751. For those members with large scopes, these two galaxies sit in a cluster of very faint galaxies, including NGC733, 736, 738, 739 740, and NGC760; all are dimmer than 12th magnitude.

Return to Epsilon then move east to the fainter member of the Triangle, Gamma (g) Tri. From here move 2 degrees just south of east to NGC925. NGC925 is a spiral galaxy with a magnitude of 10.1 that sits in a field of 10th magnitude stars; it appears as an elongated patch of light compared to the stars.

That ends the tour of Triangulum. There are a few other galaxies in this area but they are extremely faint.

Clear Skies...Eric

Copyrighted © 2000 by Stockton Astronomical Society
Lasted Updated: 11/30/2000