A galaxy contains a large percentage of stars, dust, gas, and rocks, all of which are bound together by gravity. Galaxies span thousands of light-years across and are home to anywhere from billions to trillions of stars.

Research with the sophisticated high technology telescopes that are both on Earth and in the sky has opened up a window so that we now know that there are billions and billions of galaxies in the universe.

Scientists have devoted many years to studying galaxies and have placed them in classifications by type.

As you might assume, the Pinwheel galaxy got its name because of its spiral shape. It’s well-proportioned shape has allowed it to be called “a grand design” spiral.


It is located in the Ursa Major constellation, also called the Big Dipper or “Greater Bear” in the Northern Hemisphere. The Pinwheel galaxy has around nine additional companion galaxies, including NGX 5238, UGC 8508, and UGC 9405. This grouping of galaxies is called M101 or NGC 5457.

Although the Pinwheel galaxy is around 21 million light-years from Earth, it has been viewed with the naked eye by people all over the world for thousands of years.

This galaxy is also around 70% bigger than our Milky Way galaxy, and on a clear dark night in areas that don’t have light interference from cities or towns, you can see the Pinwheel galaxy with a small telescope or binoculars.

The near-perfect spiral of the Pinwheel galaxy displays the dust lanes in the arms of the galaxy that spiral and extend all of the way around the galaxy body.

The Pinwheel galaxy is often used as an example for those interested in astronomy and space exploration. The fact that it is one of the closest galaxies to Earth has made viewing the trillions of stars a unique experience.

Pinwheel Statistics:

Galaxy Type: Spiral

Designation: M101 or NGC 5457

Diameter: 170,000 light-years

Mass: 1 billion M☉

Constellation: Ursa Major

Group: Local Group

Number of Stars: 1 trillion

Distance to Galactic Center: 21 million light-years

At around 170,000 light-years across, the Pinwheel galaxy appears as a huge spiral disk of stars, gas and dust. It has “arms” that are easy to see in the night sky and they contain nebulas that are star nurseries.

The nebulas contain giant molecular hydrogen clouds that are home to newborn stars that sprinkle out throughout the arms of the spiral.


Even though the Pinwheel galaxy was viewed by civilizations for thousands of years, it was the French astronomer, Pierre Méchain, who is given credit for the discovery of the Pinwheel galaxy in 1781.

Méchain was one of the colleagues of Charles Messier, and although he was hunting comets, he discovered the Pinwheel galaxy and then a year later many globular bodies and around 8 comets.

In 1784, William Herschel made note of a mottled nebular using his 7, 10, and 20 foot focal length reflectors in his telescope.

During the second half of the 19th century, Lord Rosse used a 72-inch diameter Newtonian reflector and observed the Pinwheel galaxy.

He is thought to be the first to ever make extensive notations on the spiral structure and created quite a few sketches.


The Pinwheel galaxy or Messier 101 is listed at an apparent magnitude of 7.9. This is the measurement of the amount of brightness that a celestial object can have to compare it with the ease of viewing with the naked eye.

On this scale, the Pinwheel galaxy is really bright and on a dark night, viewers can see the galaxy and its spiral arms.


Scientists believe that M101 could contain as many as 1 trillion stars and when you look at the arms of the spiral you can see that they are evenly distributed throughout the arm configurations.

It has an unusually high number of areas that are called H 11 regions, and these contain large, bright new stars that are ionized.

A 1991 observation discovered 1,264 of the H 11 regions in the Pinwheel galaxy, with three of them so bright that they achieved their own designations of: NGC 5461, NGC 5462 and NGC 5471.

Images using a combination of visible, X-ray and infrared wavelengths display a linear extension of around 170,000 light-years, which is nearing 70% bigger than our Milky Way galaxy.

The smaller bulge in the center is believed to have a mass that is 3 billion times the mass of the sun, but there is little or no evidence of star production in the central bulge.

M101 is called a “star maker” because it has so many areas within the galaxy for the production of new stars. It’s estimated that there are over 3,000 of these H 11 regions in the spiral arms where new stars are born.

They are given the name of H 11 because they have such a high concentration of hydrogen gas and both hydrogen and helium are the two main ingredients for stars.

The death of a star is called a supernova and their brightness can be so extreme that they block out the light of other galaxies around them.

Supernovas are the main source of the universe’s heavy elements and are critical for the formation of other celestial objects. Astronomers have recorded at least four supernovas in the Pinwheel galaxy.

They also recorded a “red nova,” which is the result of two stars colliding, exploding, and then becoming one.

M101 - noting Type Ia supernova SN 2011fe

Interesting Information:

  • Almost all galaxies have a black hole. We say “almost” because the Pinwheel galaxy is one of those that doesn’t have a center containing a black hole. Instead, the galaxy seems to contain a large quantity of x-ray sources, which are stellar-mass black holes. These form after a star dies and the remaining material falls into the stellar-mass black holes, heats up, and then sends out x-rays.
  • The Pinwheel galaxy is 21 million light-years from Earth and is called the “Face-on Spiral Galaxy.”
  • When you look at the Pinwheel galaxy at night you are seeing the light that traveled to Earth over 21 million years ago. That light was shining before humans existed on our planet.
  • The Pinwheel galaxy has a mass that’s equal to the mass of putting 100 billion suns together.
  • Some astronomers define the Pinwheel galaxy as a weakly-barred spiral galaxy.
  • The number of regions in the Pinwheel galaxy where stars are born is so high that it sets the record for the largest quantity found in any similar galaxy observed so far.
  • The central bulge of the Pinwheel galaxy is somewhat small when compared to the entire size of the galaxy. The weight of the bulge is only around the mass of 3 billion suns.
  • The arms of the Pinwheel galaxy are incredibly bright due to the number of star nurseries that they contain. However, the central bulge isn’t as bright because there are almost no new stars that are born in this area.
  • One side of the Pinwheel galaxy is asymmetrical, or off-balance. Scientists think that the Pinwheel galaxy had some sort of encounter with another galaxy in the past, with the possibility that another galaxy had a collision with the Pinwheel galaxy.

Exploration and Research:

The unusual shape of the Pinwheel galaxy is believed to be caused by light clouds and gas that is between to rather big stars that are orbiting close together.

In 2006, the ESA (European Space Agency) and NASA worked together to produce an incredible photo of the Pinwheel galaxy that shows more details than ever before seen.

Taken by the Hubble Space Telescope, the image included several layers and is kind of like viewing it with night-vision goggles, x-ray visions, a regular camera, and an ultra-violet camera simultaneously.

Due to its apparent magnitude of 7.86, astronomers can view the Pinwheel galaxy using a variety of sophisticated, high-technology telescopes.

Various space agencies around the globe have contributed to the data being collected on M101.

Listed as a “face-on” galaxy, viewing with medium-sized telescopes still requires a clear, dark, moonless sky.

In 2001, the Chandra X-ray Observatory discovered the X-ray source P98 as an ultra-luminous X-ray source and gave it the designation of M101 ULX-1.

This is defined as the type that has X-ray emissions that are more powerful than a single star, but not as powerful as those from an entire galaxy.

Additional observations from the ESA’s orbiting X-ray observatory XMM-Newton and the Hubble Space Telescope discovered that the source had an optical counterpart which is indicative that it was an X-ray binary system.

Important Events:

4 supernova explosions have been recorded in the Pinwheel galaxy in the 20th century: January 1909, September 1951, January 1970, and February 2015.

A supernova has to achieve a specific level of brightness before it will be given its on designation.

2006: The largest and most detailed image of the Pinwheel galaxy, and any galaxy to date, was taken by the Hubble Space Telescope. The mosaic included 51 individual exposures and many ground-based images.

2011: The Palomar Transient Factory (PTF) detected a supernova in M101 with a magnitude of 17.2 and was given a designation of SN 2011fe. It was classified as a Type Ia supernova, which is the kind that is caused by an explosion of a white dwarf star.

2019: a paper published in the Astrophysical Journal focuses on the red colored outer ring of M101. The authors made note that this is the zone where the polycyclic aromatic hydrocarbons, organic molecules, that we see in much of M101 suddenly vanish.

The molecules are carbon-containing, dusty elements that are found in the star nurseries. The content is on Earth in our exhaust pipes, barbeque pits, and in any location where combustion has occurred.

Scientists believe that this is a critical element required for the conversion into the stuff of life. The discovery of the disappearance of the organic molecules means that organics can’t thrive in the outer regions, probably due to high radiation levels.

Facts about Pinwheel Galaxy for Kids:

  • There are over 3,000 locations in the Pinwheel galaxy’s spiral arms that are considered to be star nurseries. This means that the Pinwheel galaxy has set the record for having the most of these regions than any other similar galaxy that we have observed to date.
  • Areas that are star nurseries within a galaxy are called H 11 because they contain such high volumes of hydrogen, one of the critical elements required for new star formation.
  • The Pinwheel galaxy, also known as M101, is around twice the diameter of our own Milky Way galaxy.
  • Scientists haven’t been able to find a supermassive black hole at the center of the Pinwheel galaxy.
  • M101 seems to be part of a galaxy group that are interacting with each other on such a gravitational degree that it has caused a distortion of their shapes.
  • The Pinwheel galaxy has a center area that is symmetric but other areas of the galaxy are asymmetrical. It’s believed that this was caused from interactions with companion galaxies that are smaller, possibly creating a center displacement due to a past collision.
  • Of the nine companion galaxies, there are five that are considered to be “prominent” companions. The interaction of gravity between these galaxies is thought to be a trigger for the grand design structure of the Pinwheel galaxy and the NGC 5474 distortion.