Tag: Messier’s Catalog

Charles Messier’s Catalog, What it is and How it gives us a Quick Survey of What Sort of Objects make up this Universe of Ours. Part 2 of 2.

(Note: This blog post is the second of two posts because the subject of the objects in Messier’s catalog turned out to require a wide ranging and lengthy discussion. This is Part 2; Part 1 was published on 21 July 2018.)

In my last post I mentioned how a good night of star gazing had inspired me to write about the French astronomer Charles Messier and his catalog of 110 fuzzy objects that you can see in the night sky with binoculars or a small telescope. I mentioned how these fuzzy objects, and others like them, are now the subjects of intense study by astronomers.

I mentioned further how the Messier objects can be broadly divided into six types before I began discussing at some length three of those types, Open Star Clusters, Globular Star Clusters and Gaseous Nebula. In this post I will complete my survey by describing the remaining three types, Planetary Nebula, Supernova Remnants and finally Galaxies.

Planetary Nebula (M57 the Ring Nebula): The best known planetary nebula is the famous Ring Nebula, M57 in the constellation of Lyra. See image below. To find the Ring Nebula first find the brilliant star Vega, the third brightest star visible in the northern hemisphere and the brightest star in Lyra. The second brightest star in Lyra (β Lyra) is about a fist’s distance to the south of Vega and the Ring Nebula is near β Lyra. Be warned however, the ring nebula can be quite difficult to spot, which of course is another way of saying I often have difficulty finding it.

Ring Nebula, M57 as Photographed by the Hubble Space Telescope (Credit: NASA)

Planetary nebulas are so named because about two hundred years ago the French Mathematician Pierre-Simon Laplace hypothesized that planetary systems, like our own Solar System, formed from a disk of material around a new star. (See my blog Post of 5July2018)

Several of the objects in Charles Messier’s catalog seemed to resemble the disks of material Laplace talked about and so they were christened ‘Planetary Nebula’. Unfortunately we now know that planetary nebula are actually dying stars, stars who have used up all of their initial hydrogen fuel and who have begun burning helium. At this stage in a star’s life it puffs up to many times its previous size and begins expelling much of its outer material. It is this expelled material that forms the disk observed as the planetary nebula.

About five or six billion years from now our own Sun will become an object very much like the Ring Nebula. It will, over the course of several hundred million years expel about half of its mass back into interstellar space leaving behind only an intensely hot but nevertheless dead core known as a white dwarf star.

Supernova Remnants (M1 The Crab Nebula): To find the Crab Nebula you need to find the horns of Taurus the bull. The Crab Nebula sits between the points of the two horns, closer to and below the horn on the left. Again the Crab Nebula is not easy to spot but you can find many images of it on the web, such as the one below.

Crab Nebula as Photographed by the Hubble Space Telescope (Credit: NASA)

Not all stars die as slowly and quietly as did the star that formed the Ring Nebula. Large, heavy stars that are more than five times the mass of our own Sun are fated to end their lives as Supernovas, massive explosions that can briefly increase a star’s brilliance hundreds of billions of times. The material flung outward by the force of the supernova will become a type of nebula known as a supernova remnant.

The famous Crab Nebula in the constellation of Taurus is one of these. The supernova that gave birth to the Crab Nebula was actually observed and recorded by Chinese astronomers way back in the year 1054 C.E. Today we know that what remains of the actual star that went nova is an incredibly dense neutron star, spinning on its axis thousands of time a second spewing out radio waves in pulses making it an object known as a Pulsar. If you’d like to hear the actual radio emissions from the pulsar at the heart of the Crab nebula click on the link below to be taken to Jodrell Bank Radio Observatory’s web page of pulsar transmissions. (The Crab Nebula is the sixth one down but Pulsar Number 1 is actually a better one to listen to!)

http://www.jb.man.ac.uk/pulsar/Education/Sounds/

Galaxies (M31: The Andromeda Galaxy): So far all of the objects in Messier’s catalog that I’ve described have been members of our own galactic neighborhood. The final type of Messier objects are other galaxies of which the most famous is the Andromeda Galaxy. Andromeda is a naked eye visible object; indeed at some two million light years distance it is the farthest object that can be seen with the naked eye. The image below shows what Andromeda looks like through a powerful telescope.

The Andromeda Galaxy (Credit: NASA)

To see the Galaxy without binoculars or a telescope however you’re going to have to find REALLY dark skies because it is just a very faint smudge of light. The Galaxy itself is just off of the knee of the constellation Andromeda.

If you do succeed in finding the Andromeda Galaxy it is worth considering that that small smudge contains thousands of each of the other types of objects we’ve been talking about. It was of course the astronomer Carl Hubble who first measured the distance to Andromeda proving that it is indeed another galaxy every bit as large as our own Milky Way. By the way, the word galaxy is just Greek for Milky Way.

As I mentioned in the first part of this post, much of what we now know about the Universe comes from studying all of these objects that Charles Messier cataloged so that he wouldn’t mistake them for the comets he was searching for.

I was inspired to write this article by a very good night of stargazing during which I managed to find and spend some time studying seven of Messier’s objects. It turned out that I also managed to spot the International Space Station as it flew over New Jersey, and it was followed the Cygnus unmanned resupply module as well so I got a good look at both of them!

I’ve seen the space station dozens of times now along with NASA’s space shuttle and the Soyuz space capsule. The station itself is easy to find if you know when and where in the sky it will appear for your particular location.

Hey, ya know, that might be a good idea for another post!

Charles Messier’s Catalog, What it is and How it gives us a Quick Survey of What Sort of Objects make up this Universe of Ours. Part 1 of 2.

(Note: This blog post turned out to be more than twice as long as my usual posts so I’ve split it into two. This is Part 1 and Part 2 will follow immediately.)

We’ve had some really clear skies here in Philadelphia the last few nights, just perfect for stargazing. Two nights ago I spent a good hour observing the four planets that are visible during the evening right now, Venus, Mars, Jupiter and Saturn. However last night I wanted to see some deep space objects. Star clusters, Nebula and Galaxies.

Problem is that the light pollution inside the city is so intense that you simply can’t see anything that faint. Oh, the planets and a few of the brighter stars are easy enough to see if you can just get away from the streetlights but the fainter, more interesting objects, well just forget it.

Typical Light Pollution in a City (Credit: Tes)

So I drove over to New Jersey, halfway to the ocean in fact, to a spot I know of where I can get some ‘Dark Sky’. After letting my eyes adjust I could see thousands of stars along with the Milky Way. Taking out my binoculars I spent the next hour observing seven of the objects from Charles Messier’s catalog.

What’s Messier’s catalog you ask? Well, let me tell you.

Born in 1730 Charles Messier was the son of a minor member of the French Court. Inspired by a very spectacular ‘seven tailed’ comet in 1744 Charles got a job working at the French Naval Observatory, in those days astronomy was very important in navigating around the globe. The image below is of Charles Messier.

Charles Messier (Painting by Nicolas Ansiaume 1729-1786)

At that time the cutting edge of astronomical research was comets. Using Newton’s law of gravity Edmund Halley had predicted in 1705 that the comet now named for him would return in 1758 and when it did all of Europe went comet crazy. During his lifetime Charles Messier is credited with the discovery of thirteen comets.

As Messier spent night after night searching for comets he often came across fuzzy, comet-like objects that didn’t move against the fixed stars as a comet would. Remember, comets may have very long, stretched orbits around the Sun, but they still orbit the Sun, they still move against the background of fixed stars. Anyway, rather than being constantly sidetracked by these comet-like objects Messier began to compile a catalog of them so that he, and other astronomers could ignore them.

Messier published the ‘final’ version of this list in 1784 with 103 objects cataloged. After Messier’s death in 1817 however researchers going through his notes found that he had discovered another seven objects so astronomers now recognize 110 objects as Messier objects.

Funny thing is, Messier complied his catalog so that he wouldn’t be distracted from his comet search by them. Today however astronomers are far, far more interested in the Messier objects than they are by comets. Messier objects come in six main types; open star clusters, globular cluster, gaseous nebula, planetary nebula, supernova remnants and finally galaxies. I’ll discuss each type using a well known example from Messier’s catalog.

Open Star Clusters (M45 the Pleiades): The easiest Messier object to find is the cluster of stars known as the Pleiades or ‘Seven Sisters’ that form a very small dipper on the back of Taurus the Bull. Although six or seven stars are visible with the naked eye binoculars will show over twenty and a good telescope reveal more than a hundred. The image below shows the Pleiades with the seven sisters named but you can easily see that there are many other stars in the group as well.

The Pleiades (Credit: System Sounds)

We now know that an Open Star Cluster is what happens when a gas cloud that has given birth to several hundred or even a thousand stars is dissipated by the energy being given off by those young stars. If the gas cloud is the stellar nursery then the open cluster is the star’s kindergarten. For several million years the stars in a cluster will travel together around the milky way but in time the gravitational pulls of the rest of the galaxy causes the stars apart to drift apart. So open clusters only last for a short period of time. Four and a half billion years ago our Sun must have been in an open cluster but the Sun’s brethren are now long gone.

 

Globular Clusters (M4, Globular Cluster near the star Antares): M4 may not be the biggest Globular Cluster but I’ve always considered it to be the easiest to find because it is so near Antares, the bright red heart of the constellation Scorpio. The name Antares means the rival of Mars and because of the star’s position near the plane of the ecliptic the planet and star do sometimes come close enough to rival each other. Once you find Antares look with binoculars just a short distance to the left and you’ll see a very pale, faint cotton ball. That is the globular cluster M4. See image below.

Globular Cluster M4 (Credit: European Southern Observatory ESO)

Globular Clusters are quite mysterious and very ancient. Containing hundreds of thousands or more than a million stars globular clusters last for billions of years. In fact it appears that many of the globulars in and around the Milky Way are actually older than the Galaxy is. Some astro-physicists speculate that globular clusters are the building blocks that form galaxies but in that case, how do globular clusters form?

Gaseous Nebula (M42, The Orion Nebula): We now know that gaseous nebula are in fact the gas clouds where stars are formed. The Hubble and other space telescopes looking into gaseous nebula in the infrared spectral region have now learned much about how stars form in such gas clouds. The Orion Nebula is a very easy example of a gaseous nebula to spot because I think the constellation of Orion is one of the easiest to spot. Once you’re found Orion look for the three stars of his belt. The Orion Nebula is just a short distance below the middle star of the belt. See image below.

Orion Nebula M42 (Credit: NASA)

I’m going to end for today right here. I’ll discuss the last three types of Messier objects in Part 2 of this post coming soon.