Greetings and Salutations fellow .... bad astronomy people!

Alright, yes, I'm the new guy - the virgin, the stranger, the outsider who doesn't fit; I'm standing near the exit with my hands in my pockets, looking down at the floor - realizing for the first time that my shoes don't match and I think my fly's open. It's OK, It's OK, I'll bring it up in group. Yes, it is late (for me anyway) and I'm a full slap shot past goofy.

Yeah, I am a little self-conscious. WHY? (I hear you cry). Because I don't know anybody here and, well, I know even less about astronomy -- There. I said it. (I can tell that one of you has already made the 'kick me' sign; you're just waiting 'til I center up over the punch bowl) -- Fine! But when you all finally stop laughing, I hope someone will be kind enough to help heal my now public disgrace and humiliation over my near complete ignorance of things cosmic, by answering the question which I shall now attempt to lay at your electronic mail ... feet. Are you ready? OK - Here goes:

First of all (If you made it this far, then you should have expected I'd insert a short, pre-question preface kind of, introductory ... forward; but I digress), with my lighting quick mind, I've figured out that planets, stars, clusters, etc. are all generally moving in one direction or another in space and that such movement is determined, at least in part, by the gravitational effect of neighboring stars, galaxies, etc.

I have also been lead to believe that, for the most part, star groupings (groupings?) found in constellations are usually the product of overactive minds with way too much idle time as opposed to being stars that actually have some true physical relationship to each other.

I ALSO understand (or think that I do anyway) that some of these star groups, such as the Seven Sisters, are gravitationally bound together as open star clusters - which would account for their physical attraction one for the other and there corresponding proximity to each other when viewed from Earth. THEREFORE, (and here's why I'm sooooo confused AND I haven't found any satisfactory answer on the web or at the local library to assuage my anguish):

IF other 'non-cluster' stars in fixed constellation formations, such as the three that are located in Orion's belt, are NOT gravitationally bound to each other (and I've been lead to believe that the three in Orion's belt are not so bound; in fact, I have been further lead to believe [I'm easy that way] that they are not even in the actual linear plane or in the proximate distance to each other that they appear to be when viewed from here on Earth) AND if these same three stars continue to move in directions that are anything but in unison, as would be the case with star clusters,
THEN [and, finally, here's my question]:

WHY HAVE THEY CONTINUED TO APPEAR IN ESSENTIALLY THE SAME POSITION (RELATIVE TO EACH OTHER) AND IN THE SAME GENERAL LOCATION IN THE SKY EVER SINCE THE FIRST BAND OF NOMADIC GOAT HERDERS SAT AROUND A DESERT CAMPFIRE 3,000 YEARS AGO AND NOTICED THAT THEY MADE AN ATTRACTIVE (and very bright) STELLAR THREESOME?

Now, please, I'm OBVIOUSLY not an astronomer, I'm not a math major (hell, I needed crib notes to get past lower division college biology) so, please, be gentle (that is to say: keep it elementary; that is to say: dumb it down) when (and if) you choose to answer.

My post has been silly, but my question is sincere. I am lost as a ball in high weeds and it has been an extremely frustrating experience looking for what I though would be a simple answer to a simple question.

So with immeasurable gratitude, in advance, I throw myself on your mercy, pray that you will graciously impart just enough of your individual and/or collective knowledge to keep a very tired new guy with mismatched shoes, from doing something, well ... let's just say 'improper' ... with Orion's belt (and we all know if that happens where Orion's pants will end up).

With lightyears of cosmic love,
I remain forever,
Lost and Confused

The constellations haven't stayed in the same positions for thousands of years, but they do change very very slowly from our perspective. In fact, if you threw a suitably rabid amature astronomer back in time, she could work out how far back she had travelled by observing the changes in the positions of the stars. When I was a kid I read a science fiction story in which the involuntary time travelers did just that.

As Ronald said, the constellations do change extremely slowly. More properly, the stars in said constellations move very, very slowly with respect to us. This is because even though individually they are moving very quickly through space, they are so far away that their apparent motion is extremely tiny. The stars in Orion's Belt are about 1,000 light years away. One light year is equal to six trillion miles, so the Belt stars are about 6 quadrillion miles away, or about six hundred million times the Earth-Sun distance. So, using some trigonometry, even if the Belt stars were going half the speed of light (way faster than they are actually going), and this motion tracked perfectly perpendicular to our line of sight, they would appear to move about a thirty-fifth of a degree (assuming the Earth was perfectly stationary during this time), which is about a thirty-fifth of the width of your index finger held at arms length.

The math:

Let s1=distance between Earth and star at beginning~6E15 miles
Let s2=distance star travels in one year~3E12 miles
Let A2=angle opposite s2 (the angle the star will appear to have moved)
Then, tan(A2)=s2/s1 ; A1=arctan(s2/s1)=arctan(5E-4) ; A1~.027 degrees

Exactly. They have moved.

Just from our distance away and the time it takes, it isn't very noticable even over the course of centuries.

Had dinosaurs had astronomers, they would have seen the stars in pretty different positions. Similar, but still noticeably different.

Remember the great lengths of distance we are talking here.

The circumference of the Earth at the equator is about 40075 kilometers.

So if you were a photon, moving at light speed, you could go around the entire Earth roughly 7½ times---- In One Second.
Pretty smooth ride eh?
Hemi has got nuthin on that kind of speed.

Yet, it would still take you 4½ years to reach the very closest star to us at the speed.
The distances involved are unimaginably huge.

Imagine watching fifty snails move around on the Sahara Desert. You stand on a high peak 100 miles away and each snail is highlighted with a glowing marker.

You will think those lazy snail bums aren't moving.

Since the galaxy we are in happens to be a spiral galaxy, most of the
mass, and most of the stars, orbit in a fairly thin pancake, in pretty
much the same direction. So most stars that are close to us have low
speed relative to us. That is different from the situation in an elliptical
galaxy, where the stars go in all different directions, which means that
stars often pass by one another at high speeds. So constellations in
our part of the Milky Way last longer than constellations in places like
elliptical galaxies and globular clusters.

-- Jeff, in Minneapolis

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Welcome to BAUT!

Others have covered the distance issue. Here's a bit on this constellation. From:

http://en.wikipedia.org/wiki/Orion_(...ation)#History

The configurations of the constellation Orion roughly formed about 1.5 million years ago, because of relative slow movements of stars within the constellation from earth's perspective (especially the belt of Orion). Orion will remain visible in the night sky for the next 1 to 2 million years, making it one of the longest observable constellations, parallel to the rise of human civilization.

Most of the stars that we see with the naked eye are exceptionally bright so can be seen over great distances. But, there are stars that are relatively close and have a large proper motion. From here:

Over the course of centuries, stars appear to maintain nearly fixed positions with respect to each other, so that they form the same constellations over historical time. Ursa Major, for example, looks nearly the same now as it did hundreds of years ago. However, precise long-term observations show that the constellations change shape, albeit very slowly, and that each star has an independent motion.

Here you can see the motion of one star, as photographed over the years through telescopes:

http://en.wikipedia.org/wiki/Image:Barnard2005.gif

Bernard's star is dim, but it is both close (for a star) and moving relatively fast. If it was bright enough, people would have noticed it moving over the centuries.

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First of all, my sincere thanks to each of you who responded to my first post. Your explanations were clearly stated, informative and quite helpful (You are now collectively responsible for almost 100% of my knowledge of astronomy). Seriously, you all should be teaching somewhere (if you're not already). That having been said, I do have two (or more) questions:

(1) If these same three stars (in Orion's Belt) are relatively young (I understand they are between 1-2.5 mys old) and I think they are all blue giants (not unlike the Seven Sisters) - one may be a red giant, I'm not sure - anyway, the question is: Were they all birthed in Orion's Nebula at about the same time and, if yes, why didn't they bind together as an open star cluster? If they did, when did they break apart?

(2) The only account I found about the actual movement of these three stars (and it was at some online religious website that cited some obscure text circa 1900) suggested that two of the stars were traveling closer to each other while the third was headed in an entirely different and distancing direction (toward us? away from us? and does it matter?). Anyway, is this true and, if so (or even if not) is there a recent, understandable (i.e., layman's) text, journal or article that you could recommend that explains how and where these three stars are traveling in relation to each other and in relation to us?

I will await your timely response.

L&C

I don't know why they aren't more closely bound gravitationally, but I'm also not sure why they should be.

In any case, this APOD page provides some info on the three stars - the first three hyperlinks are particularly informative.

.

"(1) If these same three stars (in Orion's Belt) are relatively young (I understand they are between 1-2.5 mys old) and I think they are all blue giants (not unlike the Seven Sisters) - one may be a red giant, I'm not sure - anyway, the question is: Were they all birthed in Orion's Nebula at about the same time and, if yes, why didn't they bind together as an open star cluster? If they did, when did they break apart?"

Most of Orion's stars are roughly the same age, but whatever cluster they spawned in simply wasn't massive enough (or free enough from perturbation) to stay gravitationally-bound. The case was probably the same with our own Sun. As for "when", it must have been pretty recent indeed, as they are all short-lived stars.

RE Direction:
The Wiki page on each of Orion's belt's stars gives the proper motion and radial velocity. Doesn't give the direction (or rather, the position angle), though...

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The Belt stars are almost certainly not related to each other. Despite the fact that they appear right next to each other in the sky, they are in fact at vast distances from each other. IIRC the closest is something like 800 light years from us, while the most distant is nearly twice that. The same holds true for the Orion Nebula.

Its sort of like standing in New York City and being able to see St. Louis and Los Angeles along the same line of sight. It would be wrong to assume they are twin cities like Minneapolis-St. Paul.

Really? Some of the links I've gone to suggest they all are products of Orion's molecular cloud complex.

The Orion complex is certainly massive, but I don't see how all three of the belt stars could have formed in the same open cluster given that there is something like 700ly in total separation between them.

Left to right, the 3 belt stars of Orion are searchable as Alnitak, Alnilam, and Mintaka. Yes, they are all very large, very hot blue supergiants. It's a bit odd that different sources will give different distances for these stars, but I'll put my confidence on James Kaler, who says the center star, Alnilam, is about 1300 lightyears away, while the left- and right-side stars are somewhere around 800-900 lightyears. I'm presuming that they are all too far away from each other to have any significant gravitational effect.

I believe each of these stars has "close-by" orbiting companions. Mintaka is a double and consists of a hot (30,000 Kelvin) class B, slightly evolved, giant star and a somewhat hotter class O star, each radiating near 90,000 times the solar luminosity. These are very big, very massive, very hot young stars that will burn their fuel quickly and ultimately explode as supernovas.

It may not answer the specific question you pose, but if there's anything you want to know about stars, how they're different, how they are born, evolve, and die, check out Kaler's Extreme Stars, At the Edge of Creation.

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Yeah, those are the pages linked for each star on the APOD page I mentioned earlier. I guess Kaler is The Man?

As I was looking back over this thread I was thinking, Oh, I should have looked over that link of yours.

Yes, I've read a couple of James Kaler's books... and learned a lot. Unlike many other authors (or their publishers) he assumes his readers have some intelligence. He doesn't dumb down the material, but he explains it well, and I'm sure it would be comprehensible to anyone here on BAUT.

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Think of how long it takes you to go a few miles to the nearest WalMart.

Then look at the horsehead nebula.

That sucker is TRILLIONS of miles from top to bottom.

I'm just now reading this thread, and I was about to say what Cougar said. I looked at Jim's SOW pages on Orion, etc., just last week and remember that he said only Betelguese was the only non-related star in the constellation. The man has spent decades doing public outreach and such, so I'm sure he made sure his information was accurate. (This was after decades of research in astronomy.)


Cougar, if you like his books, you should really hear him speak. His astro 101 lectures were the best things I'd ever heard, and that was as his TA. I only hope my lectures can be like that in 30 or 40 years.

bobbyislostandconfused,

Gee, you seem to know an awfull lot about the stars for someone who claims to know so little about astronomy.

Where'd you pick up all the nomenclature without any study?

Typical stars in constalations are moving relative to each other a few billionth of a degree per century, some faster. If you have a way of measuring accurately, you will detect a twice per year change due to Earth's rotation around the sun. Our perspective is different in Febuary compared to August. Neil

Why so hostile, astrotech? Looking over the OP's posts, I don't see anything that is indicative of hoaxing/trolling behavior.

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Welcome to BAUT, BobbyIsLostAndConfused! It looks like you've already been given some pretty good explanations and reference sources.

Stick around, ask more questions. Folks here love to talk astronomy and show off their knowledge.

Besides, as some guy named Asimov once said, "The most exciting statement in science is not 'Eureka! (I have found it!)' but "Huh, that's funny.'"

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Your exaggerating here. The dinos left this mortal coil some 65 million years ago. In only 100,000 years, the constellations will become significantly distorted; in 3 million years, they'll all be completely unrecognizable and most long before then.

Thanks for the clarification, But I exaggerated nothing.

If you want to add to a persons post or clarify something- Do so. There is no need to do it with an accusation at the start.

You did exaggerate the amount of time required for the constellations
to become unidentifiable. I can only re-state the same facts the other
poster did: The last dinosaurs were 65 million years ago, while most of
the constellations will be unrecognizeable in less than a million years.
So the fact that you exaggerated is just a fact.

-- Jeff, in Minneapolis

I disagree.

An exaggeration would be if I made an entire post making that claim that you are claiming I am claiming.

I didn't.

I made a vague general statement. SOME stars, even in 65 million years, would appear to move very little. SOME stars would move a LOT and some may even disappear.
The constellations would be heavily distorted- but all 88? Some wouldn't be as distorted.

Rather than go into detail about a one liner- I just left it vague.


Exaggeration implies intent to mislead the reader.
So I stand by Both posts now- I did not exaggerate.

Therefore, it is not fact. It is an unwarranted accusation so both you and dtilque can back up off me about it.
If you don't like my attitude, I don't like your wording.

If you want to correct me about something I am mistaken- Do so.

Do not put out accusations and expect me to kiss your rear. I won't.

Stop being so pidantic... What Neverfly has said is right. Go back to post 4..
Taken in context he is not wrong.
Angular movement is so small at such great distances it takes some millions of years to see the movement. Whats wrong about that?

Wouldn't that be "pedantic"?

http://en.wiktionary.org/wiki/pedantic

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Well, if you ask Piers Anthony... He covers many kinds of tics including the pedan-tic and the cri-tic.

Taken out of context, he is not even left.

All stars visible to the unaided eye would move very obviously in less
than a million years. Since nearly all of those stars are brighter than
the Sun, they are nearly all shorter-lived than the Sun. Many were
born within the last few million years, and many will disappear within
the next few million years. I can believe dtilque when he said that
the constellations will all be unrecognizeable in three million years.

-- Jeff, in Minneapolis

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http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

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