Identifying galaxies within 1 MPc

On 14 Dec 2006 09:29:56 -0800, wrote:


Brian Tung kirjutas:
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 you find and manage to identify "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.


Yes, but prominently irregular. Nobody who has any business attempting
to navigate an intergalatic spacecraft, is going to be confused by the
difference between a spiral, elliptical, and irregular galaxies. The
Milky Way, Andromeda, and Triangulum, are spirals. Andromeda's two
prominent satellites, are dwarf ellipticals. The Milky way's prominent
satellites, are dwarf irregulars. Triangulum, doesn't have prominent
satellites.

If you're in the local group, if you've got a good pair of binoculars,
and if your line of sight isn't blocked, that should be enough to point
the way home.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *

Brian Tung kirjutas:
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.

Yes, fortunately it is obvious for Andromeda, at least from our
viewpoint.

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.

Wait, how?

If there is no or little extinction due to gas, how would the light
shining to our eyes depend on where we see from?

Looking at M33 along axis, it ought to have the same total brightness,
over twice the apparent area, and therefore half the surface
brightness.

Or what?

That would make it marginally easier to see,
though it would still be easily lost from light-polluted locales.

--

If there is no or little extinction due to gas, how would the light
shining to our eyes depend on where we see from?

I didn't say "little or no." I said "not much." That may be the
confusion, which I contributed to--sorry. My guess is that there's
enough extinction to make the surface brightness not much greater at its
current orientation than there would be directly face on.

--
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

In alt.books.isaac-asimov Howard Brazee wrote:
: 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.

I don't know about you, but I am sitting in one of them as I write this.

-----
Richard Schultz
Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel
Opinions expressed are mine alone, and not those of Bar-Ilan University
-----
"Logic is a wreath of pretty flowers which smell bad."

In article . com,
writes:
Where IS M32?

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

I don't think there's any direct measurement except that it's about
the same distance from the Sun as M31. Dynamical models (for example
Block et al. 2006, Nature 443, 832; preprint
http://arxiv.org/abs/astro-ph/0610543 ; see also the orbit video at
http://www.cfa.harvard.edu/press/m31_reframed.wmv ) can provide a
theoretical guess.

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

M32 is tiny; from most locations in M31, it wouldn't be in the way.

Andromeda is at Milky Way galactic latitude of about 20. Andromeda is
itself oblique to line of sight... what is the angle between Andromeda
disc and direction to Milky Way?

The Sun is about 13 degrees from the M31 plane. It would take some
geometry to work out the angle for the Milky Way center, but it won't
differ by more than a degree.

Does anyone know where the plane of M33 is?

The Sun is about 38 degrees from the M33 plane.

As others have said in this thread, any amateur astronomer with a
pair of binoculars (and suitable viewing conditions anywhere within
the Local Group) could tell which of the large Local Group spirals is
which.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

Steve Willner kirjutas:
In article . com,
writes:
Where IS M32?

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

I don't think there's any direct measurement except that it's about
the same distance from the Sun as M31. Dynamical models (for example
Block et al. 2006, Nature 443, 832; preprint
http://arxiv.org/abs/astro-ph/0610543 ; see also the orbit video at
http://www.cfa.harvard.edu/press/m31_reframed.wmv ) can provide a
theoretical guess.

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

M32 is tiny; from most locations in M31, it wouldn't be in the way.

Andromeda is at Milky Way galactic latitude of about 20. Andromeda is
itself oblique to line of sight... what is the angle between Andromeda
disc and direction to Milky Way?

The Sun is about 13 degrees from the M31 plane. It would take some
geometry to work out the angle for the Milky Way center, but it won't
differ by more than a degree.

Does anyone know where the plane of M33 is?

The Sun is about 38 degrees from the M33 plane.

As others have said in this thread, any amateur astronomer with a
pair of binoculars (and suitable viewing conditions anywhere within
the Local Group) could tell which of the large Local Group spirals is
which.

What is the Large Magellanic Cloud actually like? It looks extended. Is
it extended in one direction only, and narrow in the two other
directions? Or is it extended in two directions and thin in one
direction so that the Sun is looking edge-on at a thick disc? Or is it
actually a thin disc viewed obliquely?

What can it look like from other vantage points inside the Milky Way?

Brian Tung wrote:
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.

Very interesting. It seems to be relevant to the current sci-fi series
Battlestar Galactica who are trying to find the Earth too, from some
other point in the galaxy.

Yousuf Khan

Brian Tung wrote:
You don't even really need to know that. Just look around the other
spiral for M32 and M110; if you don't see them, you must be in M31, the
Andromeda Galaxy.

Those probably also depend on what side of the Andromeda galaxy you are
in (i.e. north or south sides of the disc).

I noticed a similar problem in your essay about finding your bearings
inside the Milky Way:

Astronomical Games: November 2001
http://astro.isi.edu/games/dimension.html

In the first step you're trying to find the Andromeda Galaxy to get your
first bearings. You first guess where it would be, and if you guess
wrong, you say you need to get back to the opposite side of the galactic
disc to find Andromeda and get your bearings from it. It seems a bit
counterproductive just to try to find your bearings based on just one
galaxy. Wouldn't it be better to have a second option for a galaxy if
you ended up on the wrong side of the disc? If Andromeda is on the south
side of the disc, then what's a good galaxy to look for in the north
side? I think all of the major galaxies we can see from Milky Way are
all in the south side aren't they (Andromeda, Triangulum, the two
Magellanic Clouds)?

Yousuf Khan

Yousuf Khan wrote:
Those probably also depend on what side of the Andromeda galaxy you are
in (i.e. north or south sides of the disc).

I noticed a similar problem in your essay about finding your bearings
inside the Milky Way:

Astronomical Games: November 2001
http://astro.isi.edu/games/dimension.html

In the first step you're trying to find the Andromeda Galaxy to get your
first bearings. You first guess where it would be, and if you guess
wrong, you say you need to get back to the opposite side of the galactic
disc to find Andromeda and get your bearings from it. It seems a bit
counterproductive just to try to find your bearings based on just one
galaxy. Wouldn't it be better to have a second option for a galaxy if
you ended up on the wrong side of the disc? If Andromeda is on the south
side of the disc, then what's a good galaxy to look for in the north
side? I think all of the major galaxies we can see from Milky Way are
all in the south side aren't they (Andromeda, Triangulum, the two
Magellanic Clouds)?

There are indeed galaxies that one can use as signposts on either side
of the galactic plane. I chose to fix on M31 to keep the essay of a
manageable length. One could use M83 on the other side of the galactic
plane.

Incidentally, we speak of the north galactic pole and the south galactic
pole, but those poles are about 60 degrees removed from the celestial
poles (where the Earth's poles point), so the north galactic pole is
only modestly north.

--
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

"YK" == Yousuf Khan writes:

YK Brian Tung wrote:
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.

YK Very interesting. It seems to be relevant to the current sci-fi
YK series Battlestar Galactica who are trying to find the Earth too,
YK from some other point in the galaxy.

I don't think so. You may recall at the end of the pilot episode an
exchange between Adama and the President. It's just after the funeral
service, when Adama steps forward and announces that he knows the
location of Earth and that that is their destination. Later, when the
two of them are alone, the President expresses surprise that he knows
the location, and he all but admits that he doesn't really know it.

--
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