constellation question

I assumed that stars in a constellation weren't actually close to each
other in space, that they only appeared close in our 2D viewing of
them, but I have a galaxy picture that would suggest otherwise.
Clarification?

"Tim923" wrote in message
...
I assumed that stars in a constellation weren't actually close to each
other in space, that they only appeared close in our 2D viewing of
them, but I have a galaxy picture that would suggest otherwise.
Clarification?

Some will be closer to each other than others, but there is no rule that
they have to be close. Some are very close, such as the Pleiades, because
that constellation is also a star cluster.
http://www.ras.ucalgary.ca/~gibson/pleiades/
In others, such as Orion, the distance of the individual stars varies a
great deal.

Naturally, the stars of all constellations will be within a certain distance
from earth (but that distance is very large). The constallations were
defined long ago by viewing the stars with the naked eye, and none of the
really distant and faint ones can be seen that way.

What does your galaxy picture suggest?

In article ,
Tim923 wrote:

I assumed that stars in a constellation weren't actually close to each
other in space, that they only appeared close in our 2D viewing of
them, but I have a galaxy picture that would suggest otherwise.
Clarification?

Your first assumption is correct: stars in the same constellation
merely happen to be positioned in approximately the same direction
from us. They can be at any distance from us. And their distances
do vary widely -- consider for instance the Summer Triangle, where
Deneb is approx. 100 times farther away than Vega or Altair. OK
the Summer Triangle is not a constellation, it is a large asterism,
but we use it frequently to orient ourselves in the sky, so the
same principle applies.



--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

In article , Laura wrote:
"Tim923" wrote in message
...
I assumed that stars in a constellation weren't actually close to each
other in space, that they only appeared close in our 2D viewing of
them, but I have a galaxy picture that would suggest otherwise.
Clarification?

Some will be closer to each other than others, but there is no rule that
they have to be close. Some are very close, such as the Pleiades, because
that constellation is also a star cluster.
http://www.ras.ucalgary.ca/~gibson/pleiades/
In others, such as Orion, the distance of the individual stars varies a
great deal.

Naturally, the stars of all constellations will be within a certain distance
from earth (but that distance is very large). The constallations were
defined long ago by viewing the stars with the naked eye, and none of the
really distant and faint ones can be seen that way.

There's no requirement that a star has to be visible to the naked eye
to be situated in a constellation. Consider for instance Proxima
Centauri: it's magnitude 14 and thus far too faint to be visible to
the naked eye, yet it is situated in the constellation Centaurus.

In ancient times, constellations were defined by the constellation
figures, and the boundaries between the constellations were very
vaguely defined. There were even areas of the sky considered to not
belong to any constellation at all. In the 1700's this situation
started to change: stellar cartographists started to draw
constellation boundaries, and new constellations were invented to
fill in the areas of the sky having no constellation. And in 1930
the IAU defined the constellation boundaries rigorously. So today,
no matter what star you consider and no matter how faint, it belongs
to a constellation. Occasionally, the proper motion of a star
carries it from one constellation to another.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

In message , Paul Schlyter
writes
In article ,
Tim923 wrote:

I assumed that stars in a constellation weren't actually close to each
other in space, that they only appeared close in our 2D viewing of
them, but I have a galaxy picture that would suggest otherwise.
Clarification?

Your first assumption is correct: stars in the same constellation
merely happen to be positioned in approximately the same direction
from us. They can be at any distance from us. And their distances
do vary widely -- consider for instance the Summer Triangle, where
Deneb is approx. 100 times farther away than Vega or Altair. OK
the Summer Triangle is not a constellation, it is a large asterism,
but we use it frequently to orient ourselves in the sky, so the
same principle applies.

There are exceptions, of course. For instance, all but two of the stars
in the Plough are part of a cluster (it's not a modern constellation,
but it used to be. I was amused to read that the Arabs originally
described the region as a bier but later adopted the bear interpretation
of many other cultures !)
--
What have they got to hide? Release the Beagle 2 report.
Remove spam and invalid from address to reply.

OK, I now think that this galaxy picture was labelling areas of stars
by constellation names one would have to look towards in the earthly
sky. That makes sense.

What does your galaxy picture suggest?

In article ,
Jonathan Silverlight wrote:

In message , Paul Schlyter
writes
In article ,
Tim923 wrote:

I assumed that stars in a constellation weren't actually close to each
other in space, that they only appeared close in our 2D viewing of
them, but I have a galaxy picture that would suggest otherwise.
Clarification?

Your first assumption is correct: stars in the same constellation
merely happen to be positioned in approximately the same direction
from us. They can be at any distance from us. And their distances
do vary widely -- consider for instance the Summer Triangle, where
Deneb is approx. 100 times farther away than Vega or Altair. OK
the Summer Triangle is not a constellation, it is a large asterism,
but we use it frequently to orient ourselves in the sky, so the
same principle applies.

There are exceptions, of course. For instance, all but two of the stars
in the Plough are part of a cluster (it's not a modern constellation,
but it used to be.

That's not an exception of "the rule", which merely says that stars
within one constellation CAN be at widely different distances. But
that's not a requirement -- stars within the same constellation can
be at more or less the same distance to us as well, and can even be
physically related, such as the Ursa Major stream you refer to here.
Other examples are the Pleiades, the Hyades, the Coma cluster, and
the Alfa Persei association. But the Ursa Major stream is the cluster
which is closest to us -- and some stars belonging to it are even
situated in other constellations, such as Sirius and also Alfa Coronae
Borealis. It has about 100 members, and our Sun is situated in the
outer parts of this "cluster", but it's not a member of it.

The Ursa Major stream even has a catalog number: Collinder 285.

http://www.seds.org/messier/xtra/ngc/uma-cl.html
http://observers.org/tac.mailing.lis...uary/0358.html


I was amused to read that the Arabs originally described the region as
a bier but later adopted the bear interpretation of many other cultures !)

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

"Paul Schlyter" wrote in message
...
In article , Laura
wrote:
"Tim923" wrote in message
...
I assumed that stars in a constellation weren't actually close to each
other in space, that they only appeared close in our 2D viewing of
them, but I have a galaxy picture that would suggest otherwise.
Clarification?

Some will be closer to each other than others, but there is no rule that
they have to be close. Some are very close, such as the Pleiades,
because
that constellation is also a star cluster.
http://www.ras.ucalgary.ca/~gibson/pleiades/
In others, such as Orion, the distance of the individual stars varies a
great deal.

Naturally, the stars of all constellations will be within a certain
distance
from earth (but that distance is very large). The constallations were
defined long ago by viewing the stars with the naked eye, and none of
the
really distant and faint ones can be seen that way.

There's no requirement that a star has to be visible to the naked eye
to be situated in a constellation. Consider for instance Proxima
Centauri: it's magnitude 14 and thus far too faint to be visible to
the naked eye, yet it is situated in the constellation Centaurus.

True, but that's a fairly recent addition to the constellation - not made at
the time Centaurus was named and the imaginary shape of it plotted :-)
So, it follows that if none of the stars in a particular patch of sky are
visible to the naked eye, they were not made part of an original
constellation. That they were made part of already existing constellation
when they were detected I don't dispute, and that has nothing to do with the
point I was making :-)


In ancient times, constellations were defined by the constellation
figures, and the boundaries between the constellations were very
vaguely defined. There were even areas of the sky considered to not
belong to any constellation at all. In the 1700's this situation
started to change: stellar cartographists started to draw
constellation boundaries, and new constellations were invented to
fill in the areas of the sky having no constellation. And in 1930
the IAU defined the constellation boundaries rigorously. So today,
no matter what star you consider and no matter how faint, it belongs
to a constellation.

And most "Home-planetarium" type software can be set to show those
boundaries. They are laid out much like the borders of modern countries -
that is using a lot of right angles :-)

Occasionally, the proper motion of a star
carries it from one constellation to another.

"Tim923" wrote in message
...
OK, I now think that this galaxy picture was labelling areas of stars
by constellation names one would have to look towards in the earthly
sky. That makes sense.

Ah, so it was like a "if you're looking for this star, look in this
constellation" type of thing?


What does your galaxy picture suggest?