Going But Not Forgotten?

I have a question for all you astronomy lovers... i've been studying our
Local Group of galaxies and find nothing about the shift, red or blue, of
the Triangulum Galaxy (M33 and NGC 598).

Of the forty or so galaxies in our LG, there are only three that are very
large. The largest, Andromeda Galaxy shows a blue shift, which means
that its motion is in our general direction (some sources say that this
galaxy is heading directly toward us, but i don't see how they can deduce
this simply from a blue shift).

Our very own Milky Way Galaxy has been measured to be moving away
from the Virgo Cluster, a large cluster of galaxies in the constellation Virgo,
a prominent Springtime star group (U.S.A.).

The Triangulum Galaxy has been found to be moving *toward* the Virgo
Cluster. Since the Triangulum and Andromeda constellations are most
prominent during Autumn, can we deduce the following?

1) The Andromeda Galaxy is also moving toward the Virgo Cluster, and

2) The Triangulum Galaxy, like Andromeda, also shows a blue shift.

I haven't been able to find the answers to these specific points in any of
my sources. You come highly recommended!

happy days and...
starry starry nights!

--
Life without love is
A lamp without oil,
Love without prejudice
A world without soil,
Tool without toil.

Paine Ellsworth

"Painius" wrote in message
...
I have a question for all you astronomy lovers... i've been studying our
Local Group of galaxies and find nothing about the shift, red or blue, of
the Triangulum Galaxy (M33 and NGC 598).

Of the forty or so galaxies in our LG, there are only three that are very
large. The largest, Andromeda Galaxy shows a blue shift, which means
that its motion is in our general direction (some sources say that this
galaxy is heading directly toward us, but i don't see how they can deduce
this simply from a blue shift).

Our very own Milky Way Galaxy has been measured to be moving away
from the Virgo Cluster, a large cluster of galaxies in the constellation
Virgo,
a prominent Springtime star group (U.S.A.).

The Triangulum Galaxy has been found to be moving *toward* the Virgo
Cluster. Since the Triangulum and Andromeda constellations are most
prominent during Autumn, can we deduce the following?


According to the Simbad data base, the mean radial velocity of M33 is -186
km/sec. This is relative to the centre of our own Galaxy. The radial
velocity relative to the Sun is +48 km/sec.

1) The Andromeda Galaxy is also moving toward the Virgo Cluster, and

2) The Triangulum Galaxy, like Andromeda, also shows a blue shift.

I haven't been able to find the answers to these specific points in any of
my sources. You come highly recommended!

happy days and...
starry starry nights!

--
Life without love is
A lamp without oil,
Love without prejudice
A world without soil,
Tool without toil.

Paine Ellsworth



--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

"Mike Dworetsky" wrote...
in message ...

According to the Simbad data base, the mean radial velocity of M33 is -186
km/sec. This is relative to the centre of our own Galaxy. The radial
velocity relative to the Sun is +48 km/sec.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

Thanks, Mike! --

So due to the Sun's motion through the Milky Way Galaxy, the
Triangulum Galaxy appears to be going away from us. But if the
radial velocity is plotted with reference to our galaxy's center,
then the Triangulum Galaxy is actually coming *toward* our
galaxy. And apparently its velocity is not as high as Andromeda's.

Now it makes sense... thanks again, Mike! very much!

Now i'm led to ask another question...

We know some things about velocity. We know for example that
a celestial object such as our Moon, a planet, a star or even a
galaxy has a velocity with respect to Earth (or to Sun, or to the
center of our galaxy) that has two main components: radial, which
is the movement toward or away, and transverse, the movement
that is *across* the sky (to the left, right, up, down, etc.).

Our Moon orbits the Earth with a velocity that is very easy to
compute because it's so close to us. The Moon's velocity has a
radial component because it is "falling toward" the Earth (yes, i
know that it appears to be falling away from Earth to the tune of
about 4 cm per year; however, i see this as falling *toward* the
Earth with less and less velocity each year).

Planets, too, are easy when it comes to computing their transverse
velocities and for the same reason: because they're so close.

With stars, the measurements become a little trickier because they
are so far away from us. It seems that the radial velocity is still
easy to compute, while the transverse component of the velocity
gets more and more difficult to measure the farther away the
celestial object is from us.

The farther away an object is, the more *time* we must wait to
be able to sense how far to the left or right the object has moved.

We now know that both of the other large galaxies in our Local
Group have a radial velocity that is in our general direction, that
is, they both show a blue shift. This could mean many things, but
i think it means that all three galaxies, Andromeda, Triangulum
and our own Milky Way are gravitationally bound to a common
center of gravity. All three are "falling toward" each other as they
revolve around... something. (What this "something" is can be
anybody's guess. Since scientists are finding huge masses of dark
matter in the center of other galaxy clusters, it may follow that our
Local Group revolves around a huge clump of this dark matter?)

So my question is this... Is there a formula to compute how long
we must wait before we can gather fairly accurate measurements
of transverse velocity? In other words...

How long would we have to wait to notice a sideways movement
of the Andromeda and/or Triangulum Galaxies? a movement of,
say, 1 mm? Would we already have to know the transverse
velocity to compute this? or is there another way to measure the
amount of time needed? (so we can use it to compute the
transverse velocity?)

Such a formula and measurement would shed an amazing amount
of light on the dynamics of our Local Group!

happy days and...
starry starry nights!

--
"Oh give me please the Universe keys
That unlock all those mysteries!"
You pay your fees, you find some keys
That keeps you always groping.

"Oh give me please the Happiness keys
That ease the pain of biting fleas!"
Today you seize you need no keys,
That door is always open.

Paine Ellsworth

"P" == Painius writes:

P With stars, the measurements become a little trickier because they
P are so far away from us. It seems that the radial velocity is
P still easy to compute, while the transverse component of the
P velocity gets more and more difficult to measure the farther away
P the celestial object is from us.

In general, yes, though I'd use the term "measure" not "compute" in
reference to velocities.

P The farther away an object is, the more *time* we must wait to be
P able to sense how far to the left or right the object has moved.

P We now know that both of the other large galaxies in our Local
P Group have a radial velocity that is in our general direction, that
P is, they both show a blue shift. This could mean many things, but
P i think it means that all three galaxies, Andromeda, Triangulum and
P our own Milky Way are gravitationally bound to a common center of
P gravity. All three are "falling toward" each other as they revolve
P around... something. (What this "something" is can be anybody's
P guess. Since scientists are finding huge masses of dark matter in
P the center of other galaxy clusters, it may follow that our Local
P Group revolves around a huge clump of this dark matter?)

Yes and no. It is probably the case that the three major galaxies are
gravitational bound together. This does not mean that there is
something "at" the common center of mass. Remember that saying one
object "orbits" another is an approximation. The Moon does not orbit
the Earth. The Earth and Moon orbit a common center of mass, which is
somewhere inside the Earth but not inside the center of the Earth.
Jupiter and the Sun orbit a common center of mass that happens to be
just outside the Sun's surface. The Milky Way, Andromeda, and
Triangulum galaxies orbit a common center of mass.

P So my question is this... Is there a formula to compute how long we
P must wait before we can gather fairly accurate measurements of
P transverse velocity? In other words...

Sure. The amount of time you have to wait is

t = (D/v)*theta

where v is the velocity of the object, D is its distance, and theta is
the size of the angle that it needs to move for you to determine that
it has moved. For instance, suppose you could observe water masers in
the Andromeda galaxy using VLBI techniques. You might hope to obtain
a resolution of about 0.3 milliarcseconds, so that you could determine
they had moved after they shifted about 1 mas (= 5 nanoradians = 5E-9
radians). Suppose that the Andromeda galaxy has a transverse velocity
of 200 km/s, and it is 750 kpc distant (= 2.3E19 km). Then t =
561777408 seconds ~ 17 years.

P How long would we have to wait to notice a sideways movement of the
P Andromeda and/or Triangulum Galaxies? a movement of, say, 1 mm?
P Would we already have to know the transverse velocity to compute
P this? or is there another way to measure the amount of time needed?
P (so we can use it to compute the transverse velocity?)

P Such a formula and measurement would shed an amazing amount of
P light on the dynamics of our Local Group!

Yes!

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

"Joseph Lazio" wrote...
in message ...

"P" == Painius writes:
. . .
P The farther away an object is, the more *time* we must wait to be
P able to sense how far to the left or right the object has moved.

P We now know that both of the other large galaxies in our Local
P Group have a radial velocity that is in our general direction, that
P is, they both show a blue shift. This could mean many things, but
P i think it means that all three galaxies, Andromeda, Triangulum and
P our own Milky Way are gravitationally bound to a common center of
P gravity. All three are "falling toward" each other as they revolve
P around... something. (What this "something" is can be anybody's
P guess. Since scientists are finding huge masses of dark matter in
P the center of other galaxy clusters, it may follow that our Local
P Group revolves around a huge clump of this dark matter?)

Yes and no. It is probably the case that the three major galaxies are
gravitational bound together. This does not mean that there is
something "at" the common center of mass. Remember that saying one
object "orbits" another is an approximation. The Moon does not orbit
the Earth. The Earth and Moon orbit a common center of mass, which is
somewhere inside the Earth but not inside the center of the Earth.
Jupiter and the Sun orbit a common center of mass that happens to be
just outside the Sun's surface. The Milky Way, Andromeda, and
Triangulum galaxies orbit a common center of mass.

Yes, thanks Joseph... Earth and Moon are a relatively simple
two-body problem with one body a bit larger than the other.
The galaxies on the other hand represent an interesting three-
(or perhaps even four-)body problem that is, as might be
expected, far more complicated.

If you go here...

http://www.arachnoid.com/gravitation/

....there is a Java orbital analysis program that can be used
to see what happens when three bodies orbit around just a
common center of mass with no actual mass in the center.

I've tried various positionings of the bodies in an effort to
approximate the relative positions of the three galaxies.
And it seems that even if the three bodies begin in a stable
orbit around the common center, the orbit quickly becomes
unstable and deteriorates. Eventually one object gets
thrown into a flattened elliptical orbit and ends up colliding
and merging with one of the other objects. And this turns
the system into a two-body problem with the merged body
larger than the other body.

It seems to me that there must be a large mass for the three
bodies to orbit in order for them to maintain fairly stable
orbits. In addition, the center mass can be expected to be
a good deal more massive than the galaxies that orbit it.

I could be wrong, but it appears to me that there may very
well be an unimaginably huge mass of dark matter out there
somewhere between our Milky Way and the two other big
galaxies in the LG. And all three galaxies maintain fairly
stable orbits around it.

One thing that hurts the feasibility of my idea is the evidence
that Andromeda and Triangulum have already experienced
a bit of a glancing collision. This may mean that you're right
after all.

P So my question is this... Is there a formula to compute how long we
P must wait before we can gather fairly accurate measurements of
P transverse velocity? In other words...

Sure. The amount of time you have to wait is

t = (D/v)*theta

where v is the velocity of the object, D is its distance, and theta is
the size of the angle that it needs to move for you to determine that
it has moved. For instance, suppose you could observe water masers in
the Andromeda galaxy using VLBI techniques. You might hope to obtain
a resolution of about 0.3 milliarcseconds, so that you could determine
they had moved after they shifted about 1 mas (= 5 nanoradians = 5E-9
radians). Suppose that the Andromeda galaxy has a transverse velocity
of 200 km/s, and it is 750 kpc distant (= 2.3E19 km). Then t =
561777408 seconds ~ 17 years.
--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

How did you come by your Andromeda Galaxy transverse
velocity supposition? Educated guess? or have we been
watching it long enough to have measured it?

happy days and...
starry starry nights!

--
A smidgeon of fear and a sprinkle of strife
And a whole lotta love till your cold...
Most everyone here wants to live a long life,
Ah! but nobody wants to get old.

Paine Ellsworth