Playing with google skyand some of the figures the constellations are presumed to represent are not (IMO) all that representative of the figures even in the sketchiest most abstract terms.
I know the relative positions of the stars as viewed from earth shift over time as we travel through the galaxy. In ancient times pre-BC times when the notion of the constellations originated were the then current appearance of the constellations more like the figures people claimed they represented?
Simple answer, no.
Thinking that the constellations we in American culture are familiar with are the only ones is typical western bias. The groupings of stars in the sky were given a million different names by a million different sky-watchers. Since no two of them ever agreed with one another, we shouldn’t expect there to be any real correlation with earth objects. They were figurative, fanciful, mythological, or convenient names.
There have been some movement of the relative positions of the stars over the last several thousand years. Thuban used to be the pole star 5000 years ago, e.g. But there hasn’t been sufficient change to make the constellations unrecognizable. Humans are simply pattern makers. Nothing more is needed.
Exactly. I liken it to finding shapes in clouds – we all see something different.
Isn’t the pole star determined by precession of the Earth on its axis, rather than movements in the relative positions of the stars?
Sure is. I should have said that that was in addition to relative motion, which is in fact small for most stars.
Precession changes the position of the celestial poles (i.e. the points around which the sky revolves as seen from Earth), but doesn’t change the relative star patterns and so has no effect on the look of the constellations (though it does affect which ones are visible at any given time and place).
The actual motion of stars (“proper motion”) does slowly change the patterns, but too slowly to be noticeable over historical timescales.
Alpha Centauri, which is a very bright star (the brightest in Centaurus, hence the name) has a proper motion of 3.7 arc seconds per year. At that rate, it moves about a half a degree (the angular diameter of the moon) in 500 years. Thus, constellations can change their shape in historical time, but for the most part it is a very slow process.
All I know is, the ancient Greeks didn’t have any teapots or ice cream cones, or they would never have called Saggitarius an archer and Boötes a shepherd. I mean, heck, the teapot even has steam coming out of its spout.
Chronos, the teapot was amazing to me when I first saw it. I had never seen it before moving to California. Saggitarius is not nearly as interesting when viewed from 45 degrees North, where I grew up.
The other stars move at similar rates, however - it’s a result of the precession of the Earth, i.e. the wobbling motion that the rotation axis of the Earth performs. It affects the entire sky as seen from our planet alike, so the relative positions of the stars to each other as seen from Earth remains the same.
Edit: I just saw that you’re talking about the actual motion of stars in space, so I revoke this post.
I believe Carl Sagan’s Cosmos discusses this in some detail.
He gave some examples of where the stars in certain constellations were in the distant past and where they would be in the distant future.
And the time intervals were very large. But over time, the stars in Orion’s belt, for example, would shift so as to not be recognizable. The stars are not only moving constantly, they are at various distances from each other… So the idea that they look like a “belt” to humans is just a fluke of where the earth is now, relative to those stars.
[Slight hijack]
Are all stars that are identified in the night sky (including all stars that make up a constellation) part of the Milky Way? Or are there “stars” that are actually galaxies so distant they look like stars?
[/end slight hijack]
Yes, all the stars visible in the sky to the naked eye are in our galaxy. Most of the stars that can be resolved by telescope are in our galaxy too.
The only extragalactic star that was briefly visible to the naked eye was the supernova SN1987A in the Large Magellanic Cloud’. My brother claims to have seen it, but he might have been mistaken - it was a fairly dim and short-lived phenomenon.
Distant galaxies don’t look like points of light, like stars, but instead appear fuzzy. The Andromeda Galaxy is such an object, and can be seen with the naked eye. The closer Magellanic Clouds, which are dwarf galaxies much closer to our own, look like separated bits of the Milky Way.
I don’t believe any more distant galaxies are naked-eye objects.
This animation shows the sky around Orion in some detail for the next 300,000 years
http://www.astronexus.com/node/82
Probably the only ‘galaxy’ that looks anything like a star is Omega Centauri, which is a large globular cluster that probably was once the heart of a dwarf galaxy.
This object was labelled as the ‘omega’ star in Centaurus by Johann Bayer in 1603, when telescopes were not yet available.
I’ve seen it from 45 north plenty of times. You have to look quick, because the whole thing will only be above the horizon at once for about an hour or so, but the shape is still quite recognizable.
There are claims for one or two others, but you need to have really good vision and perfect sky conditions.
Chronos, I didn’t have a low enough southern horizon from my normal viewing spot and was not aware of how obvious the teapot would be if I had more favorable viewing conditions.
Very few stars have proper motion that fast (Alpha Centauri is the nearest star*, which enhances its proper motion) – most of them won’t shift enough to materially affect a constellation’s appearance on a historical time scale.
*Meaning nearest to the Solar System, and not counting Proxima Centauri as a separate star.
Yes, that’s why I chose Alpha Centauri. It has the highest proper motion of any prominent star. It moves fast enough to visibly change the shape of a constellation in 500 years, but that is an exception.
It’s true that the relative positions of the stars change with time, but there hasn’t been a huge amount of motion since the days when the Greeks named the constellations*. Some of them certainly do resemble, at least roughly, what they are supposed to.
Leo the lion has a triangular body and that backwards-question-mark head that’s evidently seen as a lion’s head with its mane. Scorpio has a “J” shape, like a scorpion with its curved stinger-tail. Taurus the Bull has the V-shaped Hyades, which definitely suggest a bull’s horns. Orion is a great big rectangle with its three-star “belt”**, and it’s not hard to see a giant man there.
Other Star Patterns resemble less closely, and might be named for some other reason, or be given names for things they don’t closely represent. I’ve argued in my book Medusa that the figure traced by the constellation Perseus has changed through time, and that the star cluster now identified with his hand got assigned that function because it’s near the “radiant” of the Perseid meteor shower (the point in the sky from which the meteors seem to emanate), so that he was clearly throwing them. I’ve also suggested that the nearby constellations – Cetus, Cepheus, and Cassiopeia (along with the Gorgon Head of Algol) – got their association because they were all prominient naked-eye variable stars, all in the same region of the sky. So they all ended up in the same myth. And, in fact, represent enemies of Perseus.
In many cases, the star patterns don’t resemble anything at all. But I am reminded of a series of pictures I saw of African string figures, rather like the European “Cat’s Cradle”. Some of these resembled what they were supposed to be (“Two Stingrays”, for instance, really did look like two diamond-shaped ray bodies, each with a long tail). But most were apparently abstract forms with no obvious resemblance to their nominal counterpart (although I suspect that the static pictures didn’t convey some cases where the string figure might have been made to move in some way that suggested its namesake.)
Asterisms from other cultures follow this same pattern – some do have a close resemblance to what it’s supposed to be, but most bear little, if any, resemblance. You can only “see” so many clear resemblances, after all, in what is essentially a series of random dot patterns. Once you’ve started, though, with a few close resemblances, it’s natural to keep on going, even if the similarity isn’t close at all.
*It might be the pro-Western bias mentioned above, but I’ve found that “constellations”, as used by astronomers, only refers to the star-patterns of the ancient greeks, or the modern divisions deriving from them. Star Patterns from other cultures are called “Asterisms”.
**It has been suggested – and I concur – that Orion’s “belt” was likely seen as an erect penis, and by groups other than the Greeks.