Time and Distance Questions

Since the Orion Nebula is 1500 light years from us, when we look at it, the
light we see is actually light emitted from the Nebula 1500 years ago and
not the actual Nebula as it exists today. Is this correct?

If so, with all the light years distances between us and all those objects
out there, how does one render a view of the galaxy/universe as it exists
today? Through some kind of extrapolation?

It really dont matter....
When they say 1500 light years, it probably more likely to be mean 1000-2000
light years and probably 1000.1-2000.1 light years away now or whatever.


"desert_wanderer" wrote in message
news:V0mQb.43639$Ar1.41957@fed1read04...
Since the Orion Nebula is 1500 light years from us, when we look at it,
the
light we see is actually light emitted from the Nebula 1500 years ago and
not the actual Nebula as it exists today. Is this correct?

If so, with all the light years distances between us and all those objects
out there, how does one render a view of the galaxy/universe as it exists
today? Through some kind of extrapolation?

Space missions planned for the fairly near future such as GAIA and SIM
should refine these numbers, but the OP is correct; we see the universe
as it was, and don't usually try extrapolating to what it is "now".
The brightest stars and even the galaxies in a picture like the Hubble
Deep Field have probably died by now, but it's fairly certain that the
stars in Orion are still there. "Now" doesn't really have any meaning in
the modern picture. In a similar way, you hear a thunderclap as it was,
and the lightning has long gone.

In message , onegod
writes
It really dont matter....
When they say 1500 light years, it probably more likely to be mean 1000-2000
light years and probably 1000.1-2000.1 light years away now or whatever.


"desert_wanderer" wrote in message
news:V0mQb.43639$Ar1.41957@fed1read04...
Since the Orion Nebula is 1500 light years from us, when we look at it,
the
light we see is actually light emitted from the Nebula 1500 years ago and
not the actual Nebula as it exists today. Is this correct?

If so, with all the light years distances between us and all those objects
out there, how does one render a view of the galaxy/universe as it exists
today? Through some kind of extrapolation?
--
Save the Hubble Space Telescope!
Remove spam and invalid from address to reply.

Things change so slowly, that there really isn't much difference over 1500
years.

When you get to things that change quickly like a nova, there is a
difference, but we just wait until the light gets here and treat it as
happening then. And with galaxies far off ("In a galaxy far away...") there
can be significant differences. For example, the Quasars we see at extreme
difference have probably settled down by now and no longer look like
Quasars. In effect, we are looking back in time.

So on the scale of stars near enough to see with the eyes, there isn't much
change. As you go farther out, the difference increases between actual
reality at this moment and what we see.

But it still isn't worth worrying about until you really get out there a
ways.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

************************************
"desert_wanderer" wrote in message
news:V0mQb.43639$Ar1.41957@fed1read04...
Since the Orion Nebula is 1500 light years from us, when we look at it,
the
light we see is actually light emitted from the Nebula 1500 years ago and
not the actual Nebula as it exists today. Is this correct?

If so, with all the light years distances between us and all those objects
out there, how does one render a view of the galaxy/universe as it exists
today? Through some kind of extrapolation?

"Jonathan Silverlight" wrote
in message ...
Space missions planned for the fairly near future such as GAIA and SIM
should refine these numbers, but the OP is correct; we see the universe
as it was, and don't usually try extrapolating to what it is "now".
The brightest stars and even the galaxies in a picture like the Hubble
Deep Field have probably died by now, but it's fairly certain that the
stars in Orion are still there. "Now" doesn't really have any meaning in
the modern picture. In a similar way, you hear a thunderclap as it was,
and the lightning has long gone.

Surely you jest... if the average life of a star is 10,000,000,000 years,
and stars which do not explode fade, then the chances that the "brightest"
stars we see in the sky (all of which are in our own galaxy) faded (a
process which takes millions of years), at exactly the rgiht time for them
to be still visible to us, but actually "dead" would pretty much approach
zero. It's pretty certain almost every star you can see in the sky is still
there.

In message k.net,
Kilolani writes
"Jonathan Silverlight" wrote
in message ...
Space missions planned for the fairly near future such as GAIA and SIM
should refine these numbers, but the OP is correct; we see the universe
as it was, and don't usually try extrapolating to what it is "now".
The brightest stars and even the galaxies in a picture like the Hubble
Deep Field have probably died by now, but it's fairly certain that the
stars in Orion are still there. "Now" doesn't really have any meaning in
the modern picture. In a similar way, you hear a thunderclap as it was,
and the lightning has long gone.

Surely you jest... if the average life of a star is 10,000,000,000 years,
and stars which do not explode fade, then the chances that the "brightest"
stars we see in the sky (all of which are in our own galaxy) faded (a
process which takes millions of years), at exactly the rgiht time for them
to be still visible to us, but actually "dead" would pretty much approach
zero. It's pretty certain almost every star you can see in the sky is still
there.

Ah, but the bright stars in Orion have lifespans much less than 10
billion years. For instance Rigel is about 30,000 x as bright as our sun
and won't last anything near as long (100 million years - can't
remember) Eta Carinae is another good candidate for a supernova, and
it's a long way away. I was exaggerating, but that's all.
--
Save the Hubble Space Telescope!
Remove spam and invalid from address to reply.

"Jonathan Silverlight" wrote
in message ...
In message k.net,
Kilolani writes
"Jonathan Silverlight"
wrote
in message ...
Space missions planned for the fairly near future such as GAIA and SIM
should refine these numbers, but the OP is correct; we see the universe
as it was, and don't usually try extrapolating to what it is "now".
The brightest stars and even the galaxies in a picture like the
Hubble
Deep Field have probably died by now, but it's fairly certain that the
stars in Orion are still there. "Now" doesn't really have any meaning
in
the modern picture. In a similar way, you hear a thunderclap as it was,
and the lightning has long gone.

Surely you jest... if the average life of a star is 10,000,000,000 years,
and stars which do not explode fade, then the chances that the
"brightest"
stars we see in the sky (all of which are in our own galaxy) faded (a
process which takes millions of years), at exactly the rgiht time for
them
to be still visible to us, but actually "dead" would pretty much approach
zero. It's pretty certain almost every star you can see in the sky is
still
there.

Ah, but the bright stars in Orion have lifespans much less than 10
billion years. For instance Rigel is about 30,000 x as bright as our sun
and won't last anything near as long (100 million years - can't
remember) Eta Carinae is another good candidate for a supernova, and
it's a long way away. I was exaggerating, but that's all.
--
I still maintain that because stars take millions of years to dim, with the
exception of supernovae, the chances that you are seeing a star that is no
longer there are pretty close to zero.

"desert_wanderer" wrote in message news:V0mQb.43639$Ar1.41957@fed1read04...
Since the Orion Nebula is 1500 light years from us, when we look at it, the
light we see is actually light emitted from the Nebula 1500 years ago and
not the actual Nebula as it exists today. Is this correct?

If so, with all the light years distances between us and all those objects
out there, how does one render a view of the galaxy/universe as it exists
today? Through some kind of extrapolation?

First, physical things like stars and gas clouds move very very slowly
compared with the speed of light. Distant objects in the galaxy move,
relative to us, on the order of a few hundred kilometers per second.
Closer objects, like in adjacent spiral arms (i.e. most of everything
we can see) move only a tenth of that or less.

The speed of light, on the other hand, is 300 thousand kilometers per
second. At less than a tenth of a percent of lightspeed, by
definition even the fastest-moving object, moving at right angles to
its distance from us and all the way across the galaxy, will have
moved less than a third of a degree from its current celestial
position in the time it takes its light to reach us.

Besides, when talking about such huge distances, simultaneity is
mostly meaningless -- "as it exists today" means nothing more than "as
it appears to us today". Events that happen in one order to someone
at rest wrt the core of the galaxy might happen in a different order
to someone traveling across the disc of the galaxy at some
relativistic velocity. If the light from an event hasn't reached us
yet, there's no real way to say that the event has already happened,
as far as we're concerned. The way the galaxy looks to us is as good
a reference point as any other. We can extrapolate its past or future
appearance, but that would be pure extrapolation; extrapolating the
Orion Nebula's position 1500 years from now is no different than
extrapolating its position 100 years from now or 50000 years from now.
It's still extrapolation, and the 1500 year extrapolation has no
special significance to anything except that it's where we'll see
light from it when light has traveled a distance equal to its distance
from us.

There is no simultaneous "right now" once you separate things by a
noticeable amount of lightspeed time.

Kilolani wrote:

"Jonathan Silverlight" wrote
in message ...
Space missions planned for the fairly near future such as GAIA and SIM
should refine these numbers, but the OP is correct; we see the universe
as it was, and don't usually try extrapolating to what it is "now".
The brightest stars and even the galaxies in a picture like the Hubble
Deep Field have probably died by now, but it's fairly certain that the
stars in Orion are still there. "Now" doesn't really have any meaning in
the modern picture. In a similar way, you hear a thunderclap as it was,
and the lightning has long gone.

Surely you jest... if the average life of a star is 10,000,000,000 years,
and stars which do not explode fade, then the chances that the "brightest"
stars we see in the sky (all of which are in our own galaxy) faded (a
process which takes millions of years), at exactly the rgiht time for them
to be still visible to us, but actually "dead" would pretty much approach
zero. It's pretty certain almost every star you can see in the sky is still
there.

The galaxies in the Hubble Deep Field must be billions of light-years
away. So although we may not be able to point to particular stars
that have died while their light was 'in transit', it's pretty
certain to be the case for at least a few of the sources of the
photons that went into those images.

--
Odysseus

"Odysseus" wrote in message
...
Kilolani wrote:

"Jonathan Silverlight"
wrote
in message ...
Space missions planned for the fairly near future such as GAIA and SIM
should refine these numbers, but the OP is correct; we see the
universe
as it was, and don't usually try extrapolating to what it is "now".
The brightest stars and even the galaxies in a picture like the
Hubble
Deep Field have probably died by now, but it's fairly certain that the
stars in Orion are still there. "Now" doesn't really have any meaning
in
the modern picture. In a similar way, you hear a thunderclap as it
was,
and the lightning has long gone.

Surely you jest... if the average life of a star is 10,000,000,000
years,
and stars which do not explode fade, then the chances that the
"brightest"
stars we see in the sky (all of which are in our own galaxy) faded (a
process which takes millions of years), at exactly the rgiht time for
them
to be still visible to us, but actually "dead" would pretty much
approach
zero. It's pretty certain almost every star you can see in the sky is
still
there.

The galaxies in the Hubble Deep Field must be billions of light-years
away. So although we may not be able to point to particular stars
that have died while their light was 'in transit', it's pretty
certain to be the case for at least a few of the sources of the
photons that went into those images.

I was adressing his original assertion that "the brightest stars and even
the galaxies...have probably died by now." I was not referring to a few
stars within galaxies.