Identifying galaxies within 1 MPc

If you find and manage to identify "the other galaxy".

If you're in either M31 or the Milky Way, an amateur astronomer would
find it trivial to locate the other galaxy, and identify it on the basis
of the whether M32 and M110 are present around the other galaxy.

The two brightest galaxies seen from Milky Way are the Magellanic
Clouds. The Large Magellanic Cloud is by far brighter than Andromeda,
and the Small Magellanic Cloud is also significantly brighter.

Large Magellanic Cloud is also intrinsically the brightest galaxy in
Local Group after the three of Andromeda, Milky Way and Triangulum. It
is intrinsically significantly brighter than either M32 or M110. So,
looking from Andromeda, the Large Magellanic Cloud should be far more
prominent than M32 or M110 looking from Milky Way.

All true, but irrelevant. Take a look at photos of M31. Its satellite
galaxies don't look anything like the Magellanic Clouds. The fact that
they're dimmer than the Magellanic Clouds doesn't make it any harder to
identify them. Any amateur astronomer would have little difficulty
making the distinction.

Incidentally, I have an essay on finding your way through the Milky Way
at

http://astro.isi.edu/games/dimension.html

which may be of some relevance.

And several points where I would do things differently.

I never said that it was the only way. I also never said it was the
quickest way. If you don't like it, you are welcome to write your own
essay.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
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On 14 Dec 2006 09:29:56 -0800, wrote:

The two brightest galaxies seen from Milky Way are the Magellanic
Clouds. The Large Magellanic Cloud is by far brighter than Andromeda,
and the Small Magellanic Cloud is also significantly brighter.

I suspect there are places in our galaxy where one or both of these
might be very hard to see.

Howard Brazee wrote:
The two brightest galaxies seen from Milky Way are the Magellanic
Clouds. The Large Magellanic Cloud is by far brighter than Andromeda,
and the Small Magellanic Cloud is also significantly brighter.

I suspect there are places in our galaxy where one or both of these
might be very hard to see.

Los Angeles, for one.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
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Brian Tung kirjutas:
If you find and manage to identify "the other galaxy".

If you're in either M31 or the Milky Way, an amateur astronomer would
find it trivial to locate the other galaxy,

If you are in Milky Way, it should be easier to find Large Magellanic
Cloud than Andromeda.

and identify it on the basis
of the whether M32 and M110 are present around the other galaxy.

The two brightest galaxies seen from Milky Way are the Magellanic
Clouds. The Large Magellanic Cloud is by far brighter than Andromeda,
and the Small Magellanic Cloud is also significantly brighter.

Large Magellanic Cloud is also intrinsically the brightest galaxy in
Local Group after the three of Andromeda, Milky Way and Triangulum. It
is intrinsically significantly brighter than either M32 or M110. So,
looking from Andromeda, the Large Magellanic Cloud should be far more
prominent than M32 or M110 looking from Milky Way.

All true, but irrelevant. Take a look at photos of M31. Its satellite
galaxies don't look anything like the Magellanic Clouds. The fact that
they're dimmer than the Magellanic Clouds doesn't make it any harder to
identify them.

But it does make it harder to see them to begin with.

Any amateur astronomer would have little difficulty
making the distinction.

Incidentally, I have an essay on finding your way through the Milky Way
at

http://astro.isi.edu/games/dimension.html

which may be of some relevance.

And several points where I would do things differently.

I never said that it was the only way. I also never said it was the
quickest way. If you don't like it, you are welcome to write your own
essay.

Brian Tung kirjutas:
Where IS M32?

It is between Milky Way and Andromeda. Does anyone have a clue of how
far M32 is from Andromeda?

It's unclear that it lies between us and M31. We don't know its
distance precisely enough.

It has been said that M32 should be nearer because its spectra does not
show absorption in Andromeda. But this does not tell us how far from
Andromeda.

It's possible that kinematics would tell us
where it is in relation to M31, but I'm not aware of any reliable
results.

Looking from Andromeda, Milky Way should be behind and seen through
M32... what does it look like?

No, the Milky Way would not be seen through M32, unless you are in the
correct outskirts of M31--the part of M31 that is behind M32 as seen
from our vantage point. From all other vantage points in M31 (most of
them, in other words), the Milky Way might seem close to M32 in the sky,
but it would not appear actually behind it.

Does anyone know where the plane of M33 is? Milky Way is far from that
plane, but how far?

M33 is about twice as long as it is wide, so a guess would be that the
Milky Way is 30 degrees off M33's galactic plane.

Do we know the direction? In the other words, do we have a clue of
which edge is the near edge? Same question about Andromeda.

Are the Milky Way and Andromeda visible exclusively because we happen
to be inside the plane of one and near the plane of the other? And
would they vanish from sight if viewed from higher galactic latitudes?

No, if anything, they would appear easier to see. Google "zone of
avoidance" and galaxy.

Ah yes, it is additional complucation.

For example, M33 is about twice as long as it is wide - and pretty low
surface brightness even though total brightness is 5,7.

How would M33 look from a vantage point at exact same distance, but
from its axis?

It would be exactly as long as seen from Earth. It would be as wide as
it is long, so twice wider than when seen from Earth. Would it have the
same total brightness spread over twice the area, so as to be much
dimmer? Or would it show a lot of light blocked from us, so as to be
even brighter than seen from Earth?

All true, but irrelevant. Take a look at photos of M31. Its satellite
galaxies don't look anything like the Magellanic Clouds. The fact that
they're dimmer than the Magellanic Clouds doesn't make it any harder to
identify them.

But it does make it harder to see them to begin with.

Not significantly. Try actually looking at M31 through a telescope. If
you've done that from any kind of decent skies, I think it would be hard
for you to imagine any difficulty in identifying which galaxy you were
in.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html

Brian Tung wrote:
Not necessarily. In young spiral galaxies, most light comes from young
heavy stars on main sequence, which are blue and white. Young light
stars also exist, but the young heavy stars are much brighter and
outshine them. Whereas in Milky Way globular clusters and in elliptical
galaxies, young massive stars do not exist, so those bodies consist of
individually dim old main sequence light stars, which are yellow or
red, and a few brighter old red giants which also are red.

Elliptical galaxies are said to be visibly yellow in contrast to
bluish-white spirals. Is Andromeda also perceptibly yellower than Milky
Way?

The principle is valid, yes, but I don't think M31 is significantly
different in color from the Milky Way. I suspect you could measure a
difference, but as I said in my earlier post, there doesn't seem to be
much point, since you can just look for M31's two prominent satellite
galaxies around the other galaxy. If they're there, you're in the Milky
Way; if they're not, you're in M31.

Incidentally, I have an essay on finding your way through the Milky Way
at

http://astro.isi.edu/games/dimension.html

which may be of some relevance.


Another reference which may help in orientation is *The Astronomical
Companion* by Guy Ottewell. It's a little out of date but the
progressive zoom-out charts are very informative--intra galactic or
inter.
http://www.universalworkshop.com
or maybe Amazon or your local library, perhaps.

M33 is about twice as long as it is wide, so a guess would be that the
Milky Way is 30 degrees off M33's galactic plane.

Do we know the direction? In the other words, do we have a clue of
which edge is the near edge? Same question about Andromeda.

I don't happen to know it. I think it is known, though.

How would M33 look from a vantage point at exact same distance, but
from its axis?

It would be exactly as long as seen from Earth. It would be as wide as
it is long, so twice wider than when seen from Earth. Would it have the
same total brightness spread over twice the area, so as to be much
dimmer? Or would it show a lot of light blocked from us, so as to be
even brighter than seen from Earth?

There's *some* additional extinction due to gas in M33's arms, but not
much. It would have essentially the same surface brightness, but over
twice the apparent area, so our eyes would receive twice the light from
M33 that they do now. That would make it marginally easier to see,
though it would still be easily lost from light-polluted locales.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html

wrote:
Do we know the direction? In the other words, do we have a clue of
which edge is the near edge? Same question about Andromeda.

For M31 you can ascertain the answer immediately by looking at a
photograph. For M33 it's not obvious; I don't know offhand how you'd go
about finding out.

--
"Always look on the bright side of life."
To reply by email, replace no.spam with my last name.

Russell Wallace wrote:
For M31 you can ascertain the answer immediately by looking at a
photograph.

Ahh yes, I forgot about the dust lane. Southern edge, I think.

For M33 it's not obvious; I don't know offhand how you'd go
about finding out.

Probably direction of spiral plus Doppler shift at the edges. Not 100
percent reliable as there are spiral galaxies that are known to rotate
against the direction of the arms--but that's apparently fairly rare.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html