visible galaxy

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Moderators General, Prelates

JonBanes
Posts: 53
Joined: Thu May 28, 2009 8:31 pm UTC

visible galaxy

Postby JonBanes » Thu Oct 08, 2009 5:20 am UTC

Ok, here's one for you.

How close would a galaxy have to be for us to see it in the night sky as big as the moon? Also what would it look like? Most of those pictures you see are IR and not visible spectrum pictures, i think.

Lets say it's an average sized spiral galaxy oriented so that we can see the spiral.

User avatar
BlackSails
Posts: 5315
Joined: Thu Dec 20, 2007 5:48 am UTC

Re: visable galaxy

Postby BlackSails » Thu Oct 08, 2009 5:25 am UTC

Which class is this for?

User avatar
antonfire
Posts: 1772
Joined: Thu Apr 05, 2007 7:31 pm UTC

Re: visable galaxy

Postby antonfire » Thu Oct 08, 2009 5:44 am UTC

About ten or twenty times as far away as these two. (Though, to be fair, they're not "average-sized spiral galaxies".)
Jerry Bona wrote:The Axiom of Choice is obviously true; the Well Ordering Principle is obviously false; and who can tell about Zorn's Lemma?

JonBanes
Posts: 53
Joined: Thu May 28, 2009 8:31 pm UTC

Re: visable galaxy

Postby JonBanes » Thu Oct 08, 2009 6:01 am UTC

First off, not for a class. I'm a molecular biologist. Way to jump to conclusions, it is possible for someone to be curious outside of a classroom.

Doing the simple math a spiral galaxy of 200,000 lightyears wide would need to be about 22 mil lightyears away to appear the sizeof the moon in the sky.

What would this look like? Would you be able to see the arms?

JonBanes
Posts: 53
Joined: Thu May 28, 2009 8:31 pm UTC

Re: visable galaxy

Postby JonBanes » Thu Oct 08, 2009 6:07 am UTC

antonfire wrote:About ten or twenty times as far away as these two. (Though, to be fair, they're not "average-sized spiral galaxies".)


how big is this in seconds/minutes as seen from earth and how does it compare to the moon?

User avatar
phlip
Restorer of Worlds
Posts: 7573
Joined: Sat Sep 23, 2006 3:56 am UTC
Location: Australia
Contact:

Re: visable galaxy

Postby phlip » Thu Oct 08, 2009 6:22 am UTC

JonBanes wrote:
antonfire wrote:About ten or twenty times as far away as these two. (Though, to be fair, they're not "average-sized spiral galaxies".)


how big is this in seconds/minutes as seen from earth and how does it compare to the moon?


I had to do a lot of hunting around, but I eventually found these two pages (which totally haven't been linked to yet), which give:
Small Magellanic Cloud page wrote:Apparent dimensions (V) 5° 20′ × 3° 5′
Large Magellanic Cloud page wrote:Apparent dimensions (V) 10.75° × 9.17°
Also, from here:
Moon page wrote:Angular diameter 29.3 to 34.1 arcminutes


It's possible for someone to be curious outside of a classroom, but typically such curiosity would be paired with actually looking up the answers to simple questions... whereas just blindly asking them of some forum implies the sort of disinterest that comes with homework.

Code: Select all

enum ಠ_ಠ {°□°╰=1, °Д°╰, ಠ益ಠ╰};
void ┻━┻︵​╰(ಠ_ಠ ⚠) {exit((int)⚠);}
[he/him/his]

User avatar
Tass
Posts: 1909
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: visable galaxy

Postby Tass » Thu Oct 08, 2009 7:57 am UTC

Well the Andromeda Galaxy is significantly larger in the sky than the moon, but it is only barely visible with the naked eye.

Galaxies are not so bright.

User avatar
Diadem
Posts: 5654
Joined: Wed Jun 11, 2008 11:03 am UTC
Location: The Netherlands

Re: visible galaxy

Postby Diadem » Thu Oct 08, 2009 10:21 pm UTC

Those numbers confuse me. The Apparant dimension of Andromeda is given as 190 degrees. That's over half the sky. That's only possible if are actually inside it.
It's one of those irregular verbs, isn't it? I have an independent mind, you are an eccentric, he is round the twist
- Bernard Woolley in Yes, Prime Minister

User avatar
phlip
Restorer of Worlds
Posts: 7573
Joined: Sat Sep 23, 2006 3:56 am UTC
Location: Australia
Contact:

Re: visible galaxy

Postby phlip » Thu Oct 08, 2009 10:33 pm UTC

190 minutes, I think you'll find. A bit over three degrees.

Code: Select all

enum ಠ_ಠ {°□°╰=1, °Д°╰, ಠ益ಠ╰};
void ┻━┻︵​╰(ಠ_ಠ ⚠) {exit((int)⚠);}
[he/him/his]

User avatar
ThinkerEmeritus
Posts: 416
Joined: Sat Jan 19, 2008 11:32 pm UTC

Re: visible galaxy

Postby ThinkerEmeritus » Thu Oct 08, 2009 10:35 pm UTC

Actually 190 minutes of arc[ ' is minutes, not degrees], so a little over 3 degrees.
"An expert is a person who has already made all possible mistakes." -- paraphrase of a statement by Niels Bohr
Seen on a bumper sticker: "My other vehicle is a Krebs cycle".

rflrob
Posts: 235
Joined: Wed Oct 31, 2007 6:45 pm UTC
Location: Berkeley, CA, USA, Terra, Sol
Contact:

Re: visible galaxy

Postby rflrob » Fri Oct 09, 2009 4:24 am UTC

For comparison, by the way, the moon and sun are both typically around half a degree (30 arcminutes) in apparent dimension.

If you're thinking, "that's crazy, the moon and sun can't possibly be the same size in the sky!" remember that we have total solar eclipses every once in a while, where the moon covers the sun almost perfectly. Sometimes the moon is slightly farther away (hence appears smaller), so it's slightly smaller than the sun, so we end up with an annular eclipse.
Ten is approximately infinity (It's very large)
Ten is approximately zero (It's very small)

seridos
Posts: 26
Joined: Thu Mar 12, 2009 9:08 pm UTC

Re: visible galaxy

Postby seridos » Sat Oct 10, 2009 10:13 pm UTC

Andromeda would appear much larger, but only its bright central region is bright enough to be visible.
From wikipedia:
"though it appears more than six times as wide as the full moon when photographed through a larger telescope, only the brighter central region is visible with the naked eye."

User avatar
Sir_Elderberry
Posts: 4206
Joined: Tue Dec 04, 2007 6:50 pm UTC
Location: Sector ZZ9 Plural Z Alpha
Contact:

Re: visible galaxy

Postby Sir_Elderberry » Sat Oct 10, 2009 10:55 pm UTC

Am I right in suspecting that this question is fueled by that Carl Sagan song that's been circulating?
http://www.geekyhumanist.blogspot.com -- Science and the Concerned Voter
Belial wrote:You are the coolest guy that ever cooled.

I reiterate. Coolest. Guy.

Well. You heard him.

User avatar
Charlie!
Posts: 2035
Joined: Sat Jan 12, 2008 8:20 pm UTC

Re: visible galaxy

Postby Charlie! » Sun Oct 11, 2009 5:20 am UTC

Apparent size of something some large distance away: 2*pi*R/(4*pi*distance^2)

So you need to google:
distance of the moon.
radius of the moon.
average radius of a galaxy.
Some people tell me I laugh too much. To them I say, "ha ha ha!"

User avatar
Mr Jack
Posts: 91
Joined: Fri Mar 20, 2009 7:31 am UTC
Location: Dunedin, New Zealand

Re: visible galaxy

Postby Mr Jack » Sun Oct 11, 2009 7:39 am UTC

Sir_Elderberry wrote:Am I right in suspecting that this question is fueled by that Carl Sagan song that's been circulating?


I strongly suspect so.

And that song is awesome...

User avatar
Vieto
Posts: 1558
Joined: Sun Jun 22, 2008 10:44 pm UTC
Location: Canada

Re: visible galaxy

Postby Vieto » Mon Oct 12, 2009 2:36 am UTC

Mr Jack wrote:
Sir_Elderberry wrote:Am I right in suspecting that this question is fueled by that Carl Sagan song that's been circulating?


I strongly suspect so.

And that song is awesome...


yes it is awesome.

It caused me to watch all 13 episodes of Carl Sagan's Cosmos in 3 days.

User avatar
Kow
Posts: 195
Joined: Sat Apr 19, 2008 12:37 pm UTC

Re: visible galaxy

Postby Kow » Mon Oct 12, 2009 10:03 am UTC

Vieto wrote:
Mr Jack wrote:
Sir_Elderberry wrote:Am I right in suspecting that this question is fueled by that Carl Sagan song that's been circulating?


I strongly suspect so.

And that song is awesome...


yes it is awesome.

It caused me to watch all 13 episodes of Carl Sagan's Cosmos in 3 days.

Ditto. There need to be more things like that made.
Image


Return to “Science”

Who is online

Users browsing this forum: No registered users and 14 guests