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  #1  
Old 11-26-2003, 11:52 AM
plnnr plnnr is offline
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Most distant object in space visible with the naked eye?

While laying back in the hot tub the other night and sipping very dry martinis, my wife and I were looking up at the stars and commenting on how the light has travelled such a great distance, and how we were essentially looking back in time. She asked me, and I'm asking you, the masses:

What is the most distance object that can be seen from the Earth with the naked eye and when did the light that we're just now seeing leave the object? In other words, how far back in time are we able to see?
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  #2  
Old 11-26-2003, 12:00 PM
Q.E.D. Q.E.D. is offline
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The Andromeda galaxy is about 2 million light-years distant. That's the farthest object I can think of off the top of my head. I'm sure there's other, more distant galaxies that are naked eye objects.
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Old 11-26-2003, 12:03 PM
Q.E.D. Q.E.D. is offline
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And according to this I was correct.
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  #4  
Old 11-26-2003, 12:05 PM
Squink Squink is offline
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Quote:
Originally posted by Q.E.D.
I'm sure there's other, more distant galaxies that are naked eye objects.
Or incorrect. Either way, it's the galaxt in Andromeda.
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Old 11-26-2003, 12:07 PM
Q.E.D. Q.E.D. is offline
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  #6  
Old 11-26-2003, 12:32 PM
Napier Napier is offline
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There's a galaxy in Triangulum that's further than the Andromeda galaxy. Some people can see it with the naked eye, but not everybody can.
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  #7  
Old 11-26-2003, 12:56 PM
Q.E.D. Q.E.D. is offline
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Quote:
Originally posted by Napier
There's a galaxy in Triangulum that's further than the Andromeda galaxy. Some people can see it with the naked eye, but not everybody can.
That would be M-33, which is 2.4 million light-years from us. I know I can't see it as a naked eye object.
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Old 11-26-2003, 01:31 PM
Polycarp Polycarp is offline
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M33 is naked-eye visible on nights with ideal seeing for people with perfect vision, according to what I read. M31 is the farthest the rest of us can see.

As I understand it, visible to the naked eye under ideal seeing conditions (* indicates at the edge of visibility) are:

1. Six major planets (Mercury, Venus, Mars, Jupiter, Saturn, Uranus*)

2. One minor planet/large asteroid: Vesta*

3. One satellite: the Moon

Note: The four Galilean satellites of Jupiter are, IIRC, all bright enough, at close opposition, to be naked-eye visible but are obscured by Jupiter's relative brilliance.

4. ~6,000 stars, all supergiants, giants, or relatively nearby main sequence stars of K and up spectra.

5. Several nebulae, number unknown to me.

6. One globular cluster: Omega Centauri*

7. Four galaxies: the Magellanic Clouds, M31 in Andromeda, and M33 in Triangulum*.

Everything else requires a telescope
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  #9  
Old 11-26-2003, 01:48 PM
rsa rsa is offline
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Re: Most distant object in space visible with the naked eye?

Quote:
Originally posted by plnnr
What is the most distance object that can be seen from the Earth with the naked eye and when did the light that we're just now seeing leave the object? In other words, how far back in time are we able to see?
Although 2.3 million light-years is often quoted as the distance to the Andromeda Galaxy, I believe that more recent observations suggest a distance of more like 2.9 million light-years.

The Andromeda Galaxy has a "peculiar" velocity of 100km/s towards the Milky Way. If I used the Google calculator correctly that would mean that Andromeda was a bit more distant when the light we see left it (but just by about 1000 light-years).
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Old 11-26-2003, 01:58 PM
bughunter bughunter is offline
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Quote:
Originally posted by Polycarp
4. ~6,000 stars, all supergiants, giants, or relatively nearby main sequence stars of K and up spectra.
Only about six thousand? Gee, I thought it was billions and billions. Or was Carl Sagan on drugs?

Oh.

Never mind.

Carry on.
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  #11  
Old 11-26-2003, 02:05 PM
vd vd is offline
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Quote:
3. One satellite: the Moon
One natural satellite anyway.

Quote:
7. Four galaxies: the Magellanic Clouds, M31 in Andromeda, and M33 in Triangulum*.
And the Milky Way
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  #12  
Old 11-26-2003, 02:15 PM
PetW PetW is offline
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Quote:
Originally posted by vd
One natural satellite anyway.

And the Milky Way
Can you see any non-natural satellites with the naked eye?
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  #13  
Old 11-26-2003, 02:26 PM
MC Master of Ceremonies MC Master of Ceremonies is offline
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Quote:
Originally posted by PetW
Can you see any non-natural satellites with the naked eye?
Yes, if you're looking at the right place at the right time.
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  #14  
Old 11-26-2003, 02:35 PM
Squink Squink is offline
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A type 1a supernova with an absolute magnitude of -19.5 would be just visible to the naked eye, mag. 6, at a distance of 4,104,097 light years.
Using m = M + 5log(d) - 5 ( M = absolute magnitude, d is in parsecs (3.2 LY))

You'd have to know where to look, and catch the star in the first few hours after it exploded.
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  #15  
Old 11-26-2003, 02:38 PM
vd vd is offline
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See here for when the ISS and other satellites can be seen from your location.

The ISS is quite bright and can easily be seen (at least in the suburbs).

From a dark location you can just watch for movement for 15 minutes or so, and eventually you'll see something cruising by in low earth orbit
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  #16  
Old 11-26-2003, 02:46 PM
Colophon Colophon is offline
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Quote:
Only about six thousand? Gee, I thought it was billions and billions. Or was Carl Sagan on drugs?
Oh, there are billions and billions, but you can't see most of them.
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  #17  
Old 11-26-2003, 03:13 PM
sick-boy sick-boy is offline
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The reason why you can't see them is obvious. All stars emit light with a certain power. If the energy flux from the star reaching your eye is above a certain limit ( 8,8*10^-11 w/m2) you can see the star. If not, you can't see it.

If we make some assumptions we can easily calculate the amount of visible stars. If we assume that all stars emit light like our Sun, that is, with P=3,9*10^26W, and that there are 3,5*10^-3 stars per cubic meter in the space surrounding us, we can calculate that the amount of visible stars is 3700. Not all stars emit light like Sun and their density in space is not constant, but I hope this crude model helps somebody...
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  #18  
Old 11-26-2003, 03:33 PM
Squink Squink is offline
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Quote:
Originally posted by sick-boy
The reason why you can't see them is obvious. All stars emit light with a certain power. If the energy flux from the star reaching your eye is above a certain limit ( 8,8*10^-11 w/m2) you can see the star. If not, you can't see it.
I put together a chart of the maximum distance at which various types of stars would be visible to the naked eye back in this thread: Naked eye viewing
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  #19  
Old 11-26-2003, 05:37 PM
Malacandra Malacandra is online now
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Hasn't s Doradus flared up in historical times bright enough to be a naked-eye object, and isn't that in the Lesser Magellanic Cloud? Can't find the reference at the moment. (That's barely a tenth of the distance to the Andromeda galaxy, but a single star rather than a galaxy or cluster.)
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  #20  
Old 11-26-2003, 07:31 PM
t-bonham@scc.net t-bonham@scc.net is offline
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Slightly off topic, but this site posts a new Astronomy picture of the day every day, with an explanation of each one.

Some of them are photos of the things talked about in this thread. And many of them are very interesting photos. I found one that I liked so much I used it as my PC wallpaper.
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  #21  
Old 11-26-2003, 08:48 PM
K364 K364 is offline
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Quote:
Originally posted by Polycarp

...As I understand it, visible to the naked eye under ideal seeing conditions (* indicates at the edge of visibility) are:...


6. One globular cluster: Omega Centauri*...


Everything else requires a telescope
M13, the globular cluster in Hercules is magnitude 5.8, so it is "at the edge of visibility" as well.
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