Portfolio ESO/ESA collaborations Cosmic Collisions Deep Sky Catalogue Publications About me

M33, the Triangulum Galaxy
as seen by the "Mayall" 4-meter telescope at Kitt Peak

Powered by Zoomify

Get the hi-resolution 16 Megapixel version - Get the 4 Megapixel version

The Triangulum Galaxy is a spiral galaxy approximately 3 million light years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598. The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, which includes our own Milky Way Galaxy, the Andromeda Galaxy and about 30 other smaller galaxies. It is one of the most distant permanent objects that can be viewed with the naked eye. Being a diffuse object, its visibility is strongly affected by small amounts of light pollution.

The Triangulum Galaxy was probably discovered by the Italian astronomer Giovanni Battista Odierna before 1654. The galaxy was independently discovered by Charles Messier on the night of 2526 August 1764. It was published in his Catalog of Nebulae and Star Clusters (1771) as object number 33; hence the name M33.

It was among the first "spiral nebulae" identified as such by Lord Rosse in 1850. In 192223, John Charles Duncan and Max Wolf discovered variable stars in the nebulae. Edwin Hubble showed in 1926 that 35 of these stars were classic cepheids, thereby allowing him to estimate their distances. The results were consistent with the concept of spiral nebulae being independent galactic systems of gas and dust, rather than just nebulae in the Milky Way.

With a diameter of about 50.000 light years, the Triangulum galaxy is the third largest member of the Local Group, a group of galaxies which also contains the Milky Way Galaxy and the Andromeda Galaxy, and it may be a gravitationally bound companion of the Andromeda Galaxy. Triangulum may be home to 40 billion stars, compared to 400 billion for the Milky Way, and 1000 billion stars for Andromeda.

Text adapted from Wikipedia.

This image is based on observations made with the "Nicholas Mayall" 4.0-Meter Telescope located at the Kitt Peak National Observatory (KPNO), part of the National Optical Astronomy Observatory (NOAO). Data provided by Dr. Philip Massey (Lowell Obs.) as distributed by the NOAO Science Archive. NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under a cooperative agreement with the National Science Foundation. Please, refer to for further info about the Observatory.

The dataset is part of  "The Resolved Stellar Content of Local Group Galaxies Currently Forming Stars" program. Investigators were: P. Massey (Lowell Obs.), P.  W. Hodge (UW),  G. H. Jacoby (NOAO), K. A. G. Olsen (NOAO), C. Smith (NOAO),  and S. Strong (Lowell Obs.)

The raw images taken by the scientists at the telescope were corrected over cross-talk between the amplifiers, bias corrected, flat-fielded, and rectified to the same spatial scale ("/pixel). This process involved several years of software development by the NOAO IRAF group, and took several months of experimentation and work on the investigators part to find just the right way of doing it. For the technical detail of the data reduction and the scientific purposes of the survey, please refer to the following papers:

An easily accessible description of the project can be found at

The reduced data were retrieved from the NOAO Science Archive and have been used in order to produce the color image shown here.
The filter used are: B-V-R-Ha (respectively assigned blue-green-orange-red hue). The full resolution is 7899
7968 pixel, or about 63 megapixel.

Credit: KPNO, NOAO, AURA, Dr. Philip Massey (Lowell Obs.) - Image processing (dynamic range compression, color composition, cleaning, tuning): Davide De Martin.

Use of images | Contact me

All images presented in this website are copyrighted Davide De Martin (2005-2014) otherwise noted. Reproduction or distribution of these images is not permitted without written consent. See also my policy of the use of images for further details or email me. Comments are welcome.
The astronomical images presented in this site were created with the help of the ESA/ESO/NASA FITS Liberator.