The Triangulum galaxy is also called Messier 33 or NGC 604 is spiral galaxy whose claim to fame is a small bright cluster of star forming areas in the center of the galaxy that allows it to be the biggest “star nursery” within the Andromeda, Milky Way, and Triangulum galaxies.

Because of the high volume of light, the Triangulum galaxy is one of the more popular galaxies for studying and taking images.

Triangulum Galaxy

It’s close proximity (only less than 3 million light-years), makes it one of the easiest to see and research.

The Triangulum galaxy is part of the Local Group of galaxies that also contain the Andromeda and the Milky Way galaxies.

It’s believed that it is between 10-40 billion times the mass of our sun and has a little companion galaxy known as the Pisces Dwarf galaxy.

Triangulum Statistics:

Galaxy Type: Spiral

Diameter: 60,000 light-years

Mass: 50 billion M☉

Constellation: Triangulum

Group: Local Group

Number of stars: 40 billion

Distance to Galactic Center: 3 million light-years

The Triangulum galaxy is around half the size of the Milky Way galaxy and it’s one of the galaxies that is close to the same spiral structure as the Milky Way.

The closest galaxy to our Milky Way is the Andromeda galaxy and the Triangulum galaxy is the second closest, at around 3 million light-years away. The Triangulum is part of our Local Group of galaxies which includes around 50 galaxies.


Credit for discovery of the Triangulum galaxy goes to Giovanni Battista Hodierna, an Italian astronomer that discovered the galaxy some time before 1654.

He published a book, “De systemate orbis cometici” (“About the systematics of the cometary orbit”) that included a somewhat vague reference that could have been about the Triangulum galaxy.

Later, in 1764, Charles Messier included the Triangulum galaxy as designation M33 in his Messier catalog.

William Herschel, who is most well-known as the astronomer that discovered Uranus, made note of his observations of the Triangulum galaxy in the late 1700s.

He indicated that it was a large gaseous region. At that time, many of the observations were thought to be “spiral nebula” that were part of the Milky Way galaxy.

In the 1920s, Edwin Hubble indicated that M33 was a separate stellar system, independent of the Milky Way galaxy. He based his decision on the Cepheid variable stars observations.

These are the stars that have the same brightness or luminosity no matter where they are located and are used for cosmic distance measurements in space.

At a later date, observations of the Triangulum galaxy showed that it is moving closer to the Milky Way at around 62,000 mph/100,000 kph.

There are theories held by some scientists that involve the idea that the Andromeda galaxy has gravitationally trapped the Triangulum galaxy.

Andromeda is a large galaxy that is also moving toward the Milky Way and it’s believed that it will collide in around 4 billion years.


One of the key things to note about the Triangulum galaxy is its spiral. Scientists have indicated that the dust inside of the spiral is well distributed and this has led to the idea that Triangulum may never have had an interaction with any other galaxy.

Collisions as well as near misses cause the spirals to become misshapen and the dust inside to be irregularly distributed.

Astronomers aren’t sure if the Triangulum galaxy is one of the newer members to the group of galaxies that the Milky Way belongs to.


It has taken years of research to try to untangle the Triangulum galaxy’s story, and still there is so much that astronomers don’t know and don’t understand.

The first images of the galaxy were taken by the NASA Swift satellite in 2007-2008. During that time, they were some of the “most detailed ultraviolet image of an entire galaxy ever taken.”

Scientists noted the star forming bright blues and purples in the galaxy.The Chandra X-ray data offered additional insights into the structure and content of the Triangulum galaxy.

In its images scientists view diverse range of objects in the pink shades as well as neutron stars.

The pictures also showed black holes that seem to be pulling material from the remains of supernovas and a companion star.

Infrared image of M33 taken with the Spitzer Space Telescope

The Subaru Telescope in Hawaii showed details in reds, greens, and blues of the incredible sweep of the spiral galaxy’s arms.

The Hubble Space Telescope offered additional information with regions that seem to be scattered in blue tones, revealing that the rate of star formation in the Triangulum galaxy is around 10 times higher than the Andromeda galaxy average.

These areas are made up of ionized hydrogen clouds that are called H-II regions. The discovery of this star nursery has led scientists to note that this is the largest area for the formation of stars in the entire Local Group of galaxies.

Further inspection of the Triangulum galaxy has led some astronomers to believe that Triangulum may be affected by the Andromeda galaxy’s gravitational pull and including it along the way as it barrels towards the Milky Way for an eventual collision in 4 billion years.

The apparent magnitude is the measurement of brightness that scientists use to compare what can be seen by the human eye versus those objects that require more sophisticated telescopes.

The Triangulum galaxy has an apparent magnitude of 5.7, giving it the ability to be clearly seen with the naked eye in clear, dark sky nights.

Interesting Information:

  • The Space Telescope Institute examined the star nursery of the Triangulum galaxy, which is one of its most distinctive features. In 2003 they estimated that there were over 200 blue stars in the gas cloud and described the area as “monstrous” at over 1,300 light-years across. This is larger than the Orion Nebula which is around 1,500 light-years.
  • Scientists said that if the Triangulum galaxy was the same distance from Earth as the Orion Nebula is, it would be the second brightest object in the sky, with the moon being the first.
  • The stars that are newly formed are referred to as “young stars.” The temperatures of these young stars is around 72,000 degrees F/40,000 degrees C. The largest young stars are nearing 120 times the mass of our sun and they have radiation being expelled from them that flood into the gas regions of the galaxy causing it to glow.
  • Our Local Group contains over 50 galaxies and only the Large Magellanic Cloud and Tarantula Nebula have a high number of young stars.

NGC 604, a star-forming region in the Triangulum Galaxy

Exploration and Study:

The Triangulum galaxy has been one of the most studied. The NASA Hubble Space Telescope created a mosaic portrait of this galaxy that is listed as the largest high-resolution image ever assembled.

It is made up of 54 Hubble fields of view. Astronomers feel that they are still in the beginning of mining the intense amount of data that has been generated by this and the second Hubble image collection.

In 2011, NASAs Wide-field Infrared Surveyor Explorer (WISE) located and displayed the hotspot activities within the Triangulum galaxy.

It also showed that there wasn’t much activity occurring in the center of the galaxy. However, the lack of activity was only assumed due to visible light observations.

The spiral arms areas that have been hidden within dust with visible light that shined through the infrared light exposed the locations where there are concentrations of clouds of cool gas.

Viewing the Triangulum galaxy with more sophisticated telescopes brought about a bit of a surprise as the galaxy seems to be a lot bigger than the images have made it appear.

Astronomers acknowledged that the image size difference was due to the fact that cold dust is more visible in space that the scientists assumed.

If you are looking to see the Triangulum galaxy, look for the constellation at:

Right ascension: 2.11 hours

Declination: 32.03 degrees

Visible between latitudes 90 degrees and -50 degrees

Facts about Triangulum Galaxy for Kids:

  • The Triangulum galaxy is considered to be a spiral galaxy without a central bar or having a weak central bar.
  • There is a nebula at the Triangulum galaxy core filled with dust and gas called an HII region. These are identified in galaxies as those that have the highest formation of stars.
  • The star nurseries in the Triangulum galaxy arms create so many new stars that they beat the percentage of the Andromeda galaxy.
  • The Triangulum and Andromeda galaxies have streams of embedded stars and hydrogen gas that link them together. This has led scientists to believe that they had past interactions and may have interactions again in around 2.5 billion years.
  • The close proximity and possible interaction of the Triangulum galaxy with the Andromeda galaxy might lead to the destruction of the Triangulum galaxy when Andromeda and the Milky Way collide.
  • The Triangulum galaxy is sometimes called the Pinwheel galaxy in error.
  • Both the Milky Way and Andromeda galaxies are bigger than the Triangulum galaxy.
  • Some astronomers refer to the Triangulum galaxy as an example of what they call an “inside-out” galaxy formation. This is a process where the galaxy’s inner core gas is exhausted and then begins to build up at the galaxy’s outer edges. The results of this actions ends up with the outer halo and inner core being made up of compositions that are different.
  • In 2016, an astrophotographer became famous for taking an image of the Triangulum galaxy that looks like three bubbles that are positioned inside of each other. Astronomers think that this odd occurrence is due to three different supernovae. One exploded and expanded to create the outer shell and then two more exploded to create each of the small inner shells.
  • The creation of stars in the Triangulum galaxy is so intense that astronomers have calculated that they happen at a rate of around half of the mass of our sun every year.
  • Thus far, the biggest black hole stellar mass that was discovered was in 2007 in the Triangulum galaxy. It has an estimated size of around 15 times the sun’s mass.
  • The official designation of Messier 33 means that Charles Messier, the French astronomer listed it as the thirty third object in his catalog.

Pop Culture:

Since the Triangulum galaxy is not only easily visible but has been the source of a lot of research, it has also been included as a topic and background in many science fiction books, television shows and movies.

  • E. Van Vogt’s Voyage of the Space Beagle book had a starship named Space Beagle that reaches the Triangulum galaxy.
  • In the television show Star Trek: The Next Generation, the Triangulum galaxy is the location where the USS Enterprise-D is warped to after the alien known as The Traveler influences the warp drive of the ship.
  • Television series seaQuest DSV had the last episode of the seaQuest being transported to the Triangulum galaxy.
  • Gene Roddenberry’s Andromeda included a territory within the Triangulum galaxy.
  • The video game series, Crysis, included aliens from the Triangulum galaxy.
  • The move E.T. the Extra-Terrestrial had move promotional posters that included the phrase “three million lightyears from home.” This led people to believe that the little alien character came from the Triangulum galaxy.
  • Easter eggs in film relate to hints and secrets that can offer information about the movie or other topics. In the movie E.T. the Extra-Terrestrial, there was an appearance of E.T. race in the Star Wars: Episode I- The Phantom Menace so that it was hinted that the “galaxy far, far away” was actually the Triangulum galaxy.