Explore Astronomy's Messier Objects

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The Pleiades open star cluster is part of the Messier Catalog, and is numbered M45. This is Hubble Space Telescope's view of it. NASA/ESA/STScI

In the mid-18th century, astronomer Charles Messier began studying the sky under the direction of the French Navy and its astronomer Joseph Nicolas Delisle. Messier was taxed with recording the comets he saw in the sky. Not surprisingly, as he studied the heavens, Messier came across a large number of objects that weren't comets.

Key Takeaways: The Messier Objects

  • The Messier Objects are named for astronomer Charles Messier who compiled his list in the mid 1700s while searching for comets. 
  • Today, astronomers still refer to this catalog of objects as the "M objects." Each is identified with the letter M and a number.
  • The most distant Messier object that can be seen with the naked eye is the Andromeda Galaxy, or M31.
  • The Messier Objects catalog contains information about 110 nebulae, star clusters, and galaxies.

Messier decided to compile these objects into a list that other astronomers could use as they searched the sky. The idea was to make it easier for others to ignore these objects as they, too, looked for comets.

This list eventually became known as the "Messier Catalog", and contains all objects Messier viewed through his 100-mm telescope from his latitude in France. First published in 1871, the list has been updated as recently as 1966.

What Are the Messier Objects?

Messier cataloged an amazing array of objects that astronomers still refer to today as the "M objects." Each is identified with the letter M and a number.

M13 globular cluster in the Hercules constellation
M13 is the brightest of the globular clusters in Hercules. It is the 13th object in Messier's list of "faint fuzzies.". Rawastrodata, via Creative Commons Attribution-Share-Alike 3.0. 

Star Clusters

First, there are the star clusters. With today's telescopes, it's fairly easy to look at many of Messier's clusters and pick out individual stars. Yet, back in his day, these collections of stars probably looked fairly fuzzy through his telescope. Some, such as M2, a globular cluster in the constellation Aquarius, are just barely visible to the naked eye. Others are easy to see without a telescope. These include the globular cluster M13, visible in the constellation Hercules, also known as the Hercules Star Cluster, and M45, commonly known as the Pleiades. The Pleiades is a good example of an "open cluster", which is a grouping of stars that travel together and are loosely bound together by gravity. Globulars contain thousands of hundreds of thousands of stars and are globe-shaped collections

Nebulae

Clouds of gas and dust are known as nebulae and exist throughout our galaxy. While nebulae are much dimmer than stars, some, such as the Orion Nebula or the Trifid Nebula in Sagittarius, can be seen with the naked eye under good conditions. The Orion Nebula is a starbirth region in the constellation Orion, while the Trifid is a cloud of hydrogen gas that glows (it is called an "emission nebula" for that reason), and has stars embedded in it as well.  

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The Orion Nebula as seen by the collection of instruments aboard Hubble Space Telescope. NASA/ESA/STScI

The Messier list also contains information about supernova remnants and planetary nebulae. When a supernova explodes, it sends clouds of gas and other elements hurtling through space at high speed. These catastrophic explosions occur only when the most massive stars die, those that are at least eight to ten times the mass of the Sun. The best-known M object that is a supernova explosion remnant is called M1 and is more commonly known as the Crab Nebula. It is not visible to the naked eye but can be viewed through a small telescope. Look for it in the direction of the constellation Taurus.  

The Crab Nebula
Hubble Space Telescope's view of the Crab Nebula supernova remnant. NASA/ESA/STScI

Planetary nebulae occur when smaller stars like the Sun die. Their outer layers dissipate while what's left of the star shrinks to become a white dwarf star. Messier charted a number of these, including the famous Ring Nebula, identified as M57 on his list. The Ring Nebula is not visible to the naked eye but can be found using binoculars or a small telescope in the constellation Lyra, the Harp. 

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You can see a white dwarf at the heart of the Ring Nebula. This is a Hubble Space Telescope image. The Ring Nebula consists of a white dwarf at the center of an expanding shell of gases expelled by the star. It is possible our star could end up like this. NASA/ESA/STScI.

Messier's Galaxies

There are 42 galaxies in the Messier Catalogue. They are classified by their shapes, including spirals, lenticulars, ellipticals, and irregulars. The most famous is the Andromeda Galaxy, which is called M31. It's the closest spiral galaxy to the Milky Way and can be seen with the naked eye from a good dark-sky site. It's also the most distant object that can be seen with the naked eye. It lies more than 2.5 million light-years away. All other galaxies in the Messier Catalogue are visible only through binoculars (for the brighter ones) and telescopes (for the dimmer ones). 

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At 2.5 million light-years, the Andromeda Galaxy is the closest spiral galaxy to the Milky Way. The term "light-year" was invented to handle the immense distances between objects in the universe. Later, "parsec" was developed for truly huge distances. Adam Evans/Wikimedia Commons.

A Messier Marathon: Viewing all the Objects

A 'Messier Marathon', wherein observers try to view all the Messier objects in one night, is only possible once a year, usually from mid-March to mid-April. Of course, the weather can be a factor. Observers typically begin their search for Messier objects as soon after sundown as possible. The search starts in the western part of the sky to catch a glimpse of any objects that are about to set. Then, observers work their way east to try and see all 110 objects before the sky brightens near sunrise the next day. 

A successful Messier Marathon can be quite challenging, particularly when an observer is trying to find those objects embedded in the vast star clouds of the Milky Way. Weather or clouds can obscure the view of some of the dimmer objects.

People interested in doing a Messier Marathon usually do them in conjunction with an astronomy club. Special star parties are organized each year, and some clubs give out certificates to those who manage to capture them all. Most observers practice by observing Messier objects throughout the year, which gives them a better chance of finding them during a marathon. It's not really something a beginner can do, but it is something to strive for as one gets better at stargazing. The Messier Marathons website has helpful hints for observers wanting to pursue their own Messier chase. 

Seeing Messier Objects Online

For observers who don't have telescopes, or the ability to get out and observe Charles Messier's objects, there are a number of online image resources for images. The Hubble Space Telescope has observed most of the list, and you can see many of their stunning images in the Space Telescope Science Institute's Flickr catalog.

Sources

  • Astropixels.com, astropixels.com/messier/messiercat.html.
  • “Charles Messier - Scientist of the Day.” Linda Hall Library, 23 June 2017, www.lindahall.org/charles-messier/.
  • Garner, Rob. “Hubble's Messier Catalog.” NASA, NASA, 28 Aug. 2017, www.nasa.gov/content/goddard/hubble-s-messier-catalog.
  • Torrance Barrens Dark-Sky Preserve | RASC, www.rasc.ca/messier-objects.