"Beauty is a manifestation of secret natural laws, which otherwise would have been hidden from us forever." -Johann Wolfgang von Goethe
Welcome back to another Messier Monday here on Starts With A Bang! Each Monday, we go through one of the 110 deep-sky wonders of the Messier Catalogue, some of the brightest and most prominent of the night sky wonders. Originally compiled by Charles Messier and his assistant, Pierre Méchain, in the late 18th Century, these telescopic wonders showcase the cosmic beauty and variety easily visible from our vantage point here on Earth.
Some of them are visible year-round, while others are best viewed at specific times of the year. Some are near easily-found celestial landmarks, while others require more nuanced techniques to find. Today, I'd like to introduce you to one of the most difficult Messier objects to find, despite being on prominent display all summer long: Messier 18.
The constellation of Sagittarius, home to the famous "teapot" asterism easily visible above, boasts a whopping 15 Messier objects. This isn't that surprising when you consider that it also contains the location of the center of our galaxy; there's a lot more stuff in that constellation than in most, so it's unsurprising that we'll have more young star clusters, active, star-forming regions, and interesting-looking nebulae in that direction of the sky.
But Messier 18 is a special challenge, because it's a relatively dim open cluster (invisible to the naked-eye under the best of conditions), it's very small and quite distant, it's located near no bright stars in the sky, and has to compete with the backdrop of the galactic plane on top of that!
The best way (I've found) to find this elusive object is to look north of the teapot towards the most prominent star located "atop" the teapot, the blue star μ Sagittarii. If you connect the tip of the teapot's spout (Alnasl) to μ Sagittarii, and travel about another 4 degrees, you might see a small patch of sky that appears to have a slightly greater density of stars than the galactic backdrop.
Alternatively, if you focus on μ Sagittarii in binoculars or a low-power telescope, you'll see two prominent stars (just barely visible to the naked eye) just to the north of it: 15 Sagittarii and 16 Sagittarii. If you follow the rough line connecting these three stars about 4 degrees farther -- possibly using the stellar landmarks below for guidance -- you'll have the chance to encounter the elusive Messier 18.
It's perhaps the most difficult of eleven Messier objects that are located relatively close together on the sky. At least Messier 21 has some nearby landmarks to help you out; Messier 18 is just a blip against the confusing galactic morass.
So, if-and-when you finally manage to capture this Messier object, what will you find yourself looking at?
Just a small collection of stars, denser than the surrounding regions, which was discovered for the first time by Messier himself, back on June 3, 1764. He had this to say about it:
A cluster of small stars... surrounded by slight nebulosity, this cluster is less obvious... with an ordinary telescope of 3.5-foot, this cluster appears like a nebula; but with a good telescope one sees nothing but stars.
Yet a "good" telescope to Messier would be on the low-end of amateur equipment today. Here's what a higher-quality observation looks like.
A few prominent, bright blue stars are the highlight of this cluster, concentrated narrowly in an area just about 0.2 degrees in diameter. The brightest and bluest of these are B-class stars (and as bright as B3, on a scale from 0-9), along with a few bright yellow/orange giants, which are similar stars that have run out of hydrogen fuel in their core and have become giants.
There's also a small amount of nebulosity in there -- or dust -- and this tells us the cluster is young, at only about 32 million years of age.
With an estimated distance of 4,900 light-years, this is one of the most distant Messier star clusters, some 10 times as distant as the Pleiades. Its tiny angular size means that it's only about 17 light-years in diameter, which makes it very compact for a star cluster.
Because of its distance, its location in the galactic plane, and the lack of really high-quality observations of M18, no one's really sure as to how many stars are in there. The Sky Catalog compiled in 2000 gives the (embarrassing) figure of twenty stars contained within this cluster, which is clearly a lowball estimate. (Stephen O'Meara's book ups that to 40, which is still a lowball number.)
A good image, like this one (above) by Jim Thommes, shows that there might be around 20 bright stars in there, but a deeper exposure brings out many, many more that are fainter, redder, and probably, but not definitely, members of this cluster.
I say probably because the clustering is clearly greater than it is elsewhere in space, centered on these dim objects. The dust in the area is also brought out very nicely, suggesting that these are all cluster members. But you need to do a spectroscopic study of these stars to determine what their distance is definitively, and as far as I know, one has not yet been performed.
As it stands now, the best professional image comes in the infrared, courtesy of 2MASS.
Seeing through all the dust, there are clearly hundreds of points of light centered on this cluster, but distinguishing what is a cluster member from what's not is a task that's simply beyond the data we've taken right now.
But my favorite image available of this hard-to-find cluster isn't from a professional; it's from Jim Misti of Misti Mountain Observatory!
This image is much higher resolution (and you should click on it), but to give you a feel for just what lies inside this cluster, I've rotated it 90 degrees and taken a high-resolution slice through it. As you can see, there are probably hundreds of stars inside! Whether these are cluster members or not remains an open question, but the beauty of this oft-overlooked region (and this photo, too) is, at least for me, unquestionable!
Close by the star-forming region known as the Omega Nebula (M17), these two objects may be related, but for right now, that's just speculation! In the meantime, enjoy Messier 18 in its own right.
- M1, The Crab Nebula: October 22, 2012
- M2, Messier’s First Globular Cluster: June 17, 2013
- M5, A Hyper-Smooth Globular Cluster: May 20, 2013
- M7, The Most Southerly Messier Object: July 8, 2013
- M8, The Lagoon Nebula: November 5, 2012
- M13, The Great Globular Cluster in Hercules: December 31, 2012
- M15, An Ancient Globular Cluster: November 12, 2012
- M18, A Well-Hidden, Young Star Cluster: August 5, 2013
- M20, The Youngest Star-Forming Region, The Trifid Nebula: May 6, 2013
- M21, A Baby Open Cluster in the Galactic Plane: June 24, 2013
- M25, A Dusty Open Cluster for Everyone: April 8, 2013
- M29, A Young Open Cluster in the Summer Triangle: June 3, 2013
- M30, A Straggling Globular Cluster: November 26, 2012
- M33, The Triangulum Galaxy: February 25, 2013
- M37, A Rich Open Star Cluster: December 3, 2012
- M38, A Real-Life Pi-in-the-Sky Cluster: April 29, 2013
- M40, Messier’s Greatest Mistake: April 1, 2013
- M41, The Dog Star’s Secret Neighbor: January 7, 2013
- M44, The Beehive Cluster / Praesepe: December 24, 2012
- M45, The Pleiades: October 29, 2012
- M48, A Lost-and-Found Star Cluster: February 11, 2013
- M51, The Whirlpool Galaxy: April 15th, 2013
- M52, A Star Cluster on the Bubble: March 4, 2013
- M53, The Most Northern Galactic Globular: February 18, 2013
- M57, The Ring Nebula: July 1, 2013
- M60, The Gateway Galaxy to Virgo: February 4, 2013
- M65, The First Messier Supernova of 2013: March 25, 2013
- M67, Messier’s Oldest Open Cluster: January 14, 2013
- M71, A Very Unusual Globular Cluster: July 15, 2013
- M72, A Diffuse, Distant Globular at the End-of-the-Marathon: March 18, 2013
- M74, The Phantom Galaxy at the Beginning-of-the-Marathon: March 11, 2013
- M78, A Reflection Nebula: December 10, 2012
- M81, Bode’s Galaxy: November 19, 2012
- M82, The Cigar Galaxy: May 13, 2013
- M83, The Southern Pinwheel Galaxy, January 21, 2013
- M86, The Most Blueshifted Messier Object, June 10, 2013
- M92, The Second Greatest Globular in Hercules, April 22, 2013
- M97, The Owl Nebula, January 28, 2013
- M99, The Great Pinwheel of Virgo, July 29, 2013
- M102, A Great Galactic Controversy: December 17, 2012
- M104, The Sombrero Galaxy: May 27, 2013
- M108, A Galactic Sliver in the Big Dipper: July 22, 2013
Join us next Monday for some spectacular views of yet another one of the deep-sky wonders of Messier's catalogue, only here, only on Messier Monday!
Wonderful write up and thanks for the inclusion!
Ethan, thanks for the good words on the Universe.
Just a question aside; in which direction should I look to see the face of god if I were able to look back far enough in time? In other words, if there were a BB, where would the centre be?
(PS it would be a black hole, so it wouldn't be the *face* of god you'd be looking at....)
Every point is moving away from each other. That means the centre from which everything else is moving away from is everywhere you are looking from.
So, according to you,
1) I contain the whole universe,
2) I am a black hole (from which nothing escapes)
3) Hmmm, I seem to remember a time when 'humanity' decided planet Earth was at the centre of our solar system. Sound familiar?
'Every point is moving away from each other' can also imply movement away from a central focus. Any explosion has a centre from where all particles are moving outward. Perhaps we are far enough distant from that centre for all matter to appear to be expanding at the same rate in every direction; assuming, of course, there was a BB. But, then, that would imply the universe is finite.
But that's not what those words do imply in this context. That's not what the Big Bang Theory predicts. It says that spacetime itself expanded, every point in space simultaneously, and as it expanded there was now more space and that all expanded just the same so there was for a time exponential growth.
It's just a model, not necessarily how the universe really works, but that's what the model says. There was no "center", whether the universe is finite or not. And this model makes very specific predictions that are very different from the explosion-in-space model (which would be linear expansion and have many directional effects of moving 'outward'), or other models.
The very best observational evidence for this model is the Cosmic Microwave Background. This blog has done a much better job of talking about it than I could, but suffice to say that it matches not just in concept but in precise mathematical description. Doesn't mean it's definitely true, but it's really hard to find any other way to explain it.
Hmmm, that is interesting. If every point came into existence at the same time, every point would be colliding with every neighboring point instantaneously, including space, since there was nothing before BB.
You say 'expanded' which implies growth. Yet, if everything started at the same time, everything was already filled, ergo no point had anywhere to enlarge into. Every point would, in fact, stop its neighboring point from any movement. So, what would there be? Probably one big lump. And, if it is still continuing to expand (red shift theory), it has to expand from a central core.
Except it takes time for motion to cause things to hit each other, Peter, and space is needed to make movement possible.
Before the Big Bang, there was neither.
This monkey grunting we call language isn't really good at these concepts.
"So, according to you,
1) I contain the whole universe,"
Nope. I am completely unable to see how an operable brain can manage to see that in what I said.
YOU ASKED "Where do I look for the CENTER of the universe". When answered you then claim that this answer is the ENTIRETY of the universe.
The center of a room does not contain the WHOLE of the room.
But the center of the universe does contain the entire universe.
At least according to you.
"2) I am a black hole (from which nothing escapes)"
Maybe you are. That certainly isn't anything said by me in THIS plane of reality, so maybe you are existing and percieving everything from this alternate universe, 'cos what you appear to have read doesn't exist in this one.
"3) Hmmm, I seem to remember a time when ‘humanity’ decided planet Earth was at the centre of our solar system. Sound familiar?"
Yes, it does: creotards and morons who don't like science because it dares to say that, no you're NOT a special flower and you CAN be wrong. These people then pretend any actual answer is something to do with religion, ergo their faith (which pretends that they are the universe's special flower, and everything is opinion and yours is entirely as worthwhile as anyone else's) is therefore "just as good" as science.
Peter Barratt: "You say ‘expanded’ which implies growth. Yet, if everything started at the same time, everything was already filled, ergo no point had anywhere to enlarge into."
It was space-time *itself* which was growing! It didn't grow "into" itself, it is the thing into which you're imagining it would grow. So instead of space crashing into itself somehow, when every point in space expanded, that simply means that there was *more space*. Every two points in space got farther apart because more space was being created between them. And then that new space also did the same thing.
It's tempting to pull out one of the old analogies like the inflating balloon because it shows how you can have expansion such that every point moves away from you without this meaning you're at the "center", and how this expansion isn't prevented by the parts of the balloon bumping into each other.
Which is fine as far as it goes but a balloon is an object embedded in our space-time, and that's what I'm trying to say isn't the case in the BB. It was space-time *itself* and as far as we know it isn't "embedded" in anything else. Or perhaps more importantly, the model does not at all require that it be. As in General Relativity, the geometry of space-time itself can change.
Let's start with WOW. Refer to #8, 1) your statement in #3 was 'Within you' , ergo my reply #4, 1).
Refer #8, 2). Your comment in parentheses, #3, line 2 mentions the black hole which is 'within me' according to you.
CB. Enjoying reading your comments so far, and as in many previous 'chapters'.
I have heard of the inflation theory in recent times, but do not perceive of it to be an adequate explanation of how existence began. As you say, BB is only a theory as well, so we have the right to question that theory until, hopefully, we find the answer without writing the equations to try and fit the evidence.
We have come a long way in a short time (cliche, I know), yet we still know so little of our environment (universe). We have created many yardsticks to enable us to measure length, mass, time.... But, these are only our way to be able to interpret what we perceive and relate that information to others in a way they can also understand. A minute is only a minute because we say it is. A foot is this length because that is our standard. Since we are so good at definitions, it seems we are also good at changing those definitions to suit the occasion. As you pointed out with Gen Rel, 'the geometry of space -time itself can change'.
Something to think about - If one were to travel to the edge of our visible universe in an instant, what would one see on arrival ?
Until next time .....
Well, lets start, peter.
#1 Like I've already said, you asked where the CENTER of the universe was, not where the ENTIRETY of the universe was in your original post. This was not changed in your point #1 either, so apparently you are incapable of both thought AND word recognition in written form.
#2 No, YOU said about a black hole, not me. I responded to THAT assertion. And did NOT say that that hole would be inside you. If I now say "Liquorice" will you now incredulously ask why I think you are made of liquorice, since I've said the word in your direction???
Please, Petey, show where I said the black hole was within you.
That was a creation of your own cretinous understanding.
Peter: "I have heard of the inflation theory in recent times, but do not perceive of it to be an adequate explanation of how existence began."
Well depends on what you mean by "adequate". Has science explained how the universe came into being in the form it did and we can now consider that mystery "solved" and not consider it again? Well no, not at all; a further explanation is constantly sought, along with any clues that might point in the right direction. Do you mean does it adequately explain what clues and evidence we have been able to glean from the universe? Then yes, it is beyond adequate.
If you mean inadequate in the sense that your objections raised early call into question its validity then forgive me for being blunt but you don't really understand it. If you mean inadequate in the sense that you don't like it for philosophical, aesthetic, or whatever other non-empirical reason, then to be even more blunt the universe doesn't care. It works how it works and that's what we're trying to figure out whether it makes us pleased or not.
A lot of scientists were in that boat when the evidence came in for the Big Bang and shot down all the other theories. Or good lord look at Quantum Mechanics. I don't think anybody "likes" it from an aesthetic or philosophical point of view, but so what?
"As you say, BB is only a theory as well, so we have the right to question that theory until, hopefully, we find the answer without writing the equations to try and fit the evidence."
Just a theory that has so much evidence and predictive success that none of the many other theories can even come close.
And writing the equation to fit the evidence is the only way you're ever going to get close to the reality! It's how we got Kepler's Laws, Newton's Laws of Motion and Law of Gravity, Quantum Mechanics, and many more.
The real test is can you then make new predictions or find new observations and phenomenon that still match the equation. If so, then you have a successful theory. This has happened for the Big Bang in spectacular fashion.
*Not* deriving our equations from the evidence is how we got Aristotle's Laws of Motion, which are trivially proven false by reality.
"A minute is only a minute because we say it is. A foot is this length because that is our standard."
Yet the amazing thing is that there is an empirical reality that doesn't depend on how you define these things. The number of feet light travels in a minute, the number of meters it travels in a second, the number of melnorme it travels in a zebranky, will all be in exact agreement after a unit conversion. And because of this we've been able to go from defining a meter by the length of some arbitrary rod in a storage facility in France to basing it on these measurable, physical parameters of the universe.
"As you pointed out with Gen Rel, ‘the geometry of space -time itself can change’."
In a quantitative, definite way that doesn't change based on unit definitions. Just like how velocity and distance depend on the observer but are not "subjective" in the sense of "whatever you want them to be".
"If one were to travel to the edge of our visible universe in an instant, what would one see on arrival ?"
Assuming the result is that I'm an equal distance in time away from the Big Bang then I'd probably see a universe that looks very much like what we see here. If I looked back towards where earth was I'd see nothing but the CMB. If I went a little less far, then I might be able to see the early stages of formation of the Milky Way. Hopefully I would be able to travel back to earth and share my findings.
"“A minute is only a minute because we say it is. A foot is this length because that is our standard.”
Yet the amazing thing is that there is an empirical reality that doesn’t depend on how you define these things"
Indeed, the distance between London and Winchester was the same when it was measured in Leagues, miles or kilometers.
Petey's problem is that he's not really interested in anything other than proclamations against science.
Thanks, CB. Yes, I do not understand any of the mathematics of BB, ergo the need to prod & question it until it makes sense, to me. If I do not question, I do not learn. I spend many a night at the telescope, looking in wonderment at all there is to see. I can never hope to understand every aspect of our existence, just to be able to appreciate it may be all that I need.
I appreciate your comments, so do not be harsh, or judgemental; I am a mere beginner on my path through life.
Yes, at the edge of the visible universe, for you, would imply equal distance from BB. Yet, you would still be in the same universe, just another part of it, wouldn't you think?