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keta
2006-Apr-09, 08:44 AM
There is a couple of telescopes iv been looking at and im wondering what distances they can see in light years im pretty sure you can tell me by this informationg , one telescope has a magnitude of 20 and a redshift of 2 and another one was a magnitude of 17.5 i dont know the redshift tho , and the last one has a magnitude of 14.7 , i no big differnces :) , neways if anyone could tell me there seeing distance in light years roughly would be great :) thx.

astromark
2006-Apr-09, 10:10 AM
You are going to get horribly confused by the mass of numbers that can be thrown up when talking of telescopes and, their power's. What really matters for you is what is it you want from your telescope?
If its easy set up and portability then what you want is not the same as the want for a large diameter motor driven reflector. Just quoting numbers is not the answer you are looking for. Yes the larger size reflector type will gather more light. Its magnification power is going to be impressive but, its only as good as the sight its located at. A much smaller scope can be far more use as its more portable and able to be transported to darker sky sites for better seeing. The word you have used 'magnitude' usually relates to the apparent brightness of objects viewed. The unaided human eye is good for only about mag 7. With telescopes located in dark sky locations they can see down to 14 mag ( some debate will be forthcoming ) you will get the idea i think. More powerful and stronger scopes are not always the best or most useful. Much has been said about all this in other threads of this forum. I sagest you have a good browse

astromark
2006-Apr-09, 10:42 AM
To respond correctly to your question; and, welcome to this forum.
Those globular clusters that we see any clear night from our modest 8 inch dobi., telescope. about 17,000 thousand light years to Omega cent., and then looking further out to those dim yet visible galaxies, its about 260,000,000 light years. Some of those professional astronomers are imaging objects at the limit of our abilities and, thats near to 13.7 billion light years away. But not from my back yard.

keta
2006-Apr-09, 11:25 AM
thanks for the reply and the welcome :) about what you have said i no wat magnitude means and i no everything u said there :) and wat i want is a telescope that will let me see as far as posible but not to expensive and you should be able to work out distances from redshift at least , i no magnitude u cant really work out but u cud get a rough idea soo id really like to no wat distances those magnitudes wud b able to see ? 1 million 10 million 100 million 1 billion light years ? thats kinda information i wanna no :) like 20 magnitude = ? light years? and same for other 2 magnitudes i put up there 17.5 and 14.7 thx :)

cjl
2006-Apr-09, 02:52 PM
it is a LARGE scope if it claims a limiting magnitude of 20, or even 17. Most 10" scopes are limited to about magnitude 15, and a decent 8" dob should see down to 14th magnitude. However, if you're looking at specific scopes, there are a range of features that need to be compared, and the limiting magnitude is only one. Which scopes are you looking at, and what do you want to use them for?

antoniseb
2006-Apr-09, 03:03 PM
thats kinda information i wanna no :) like 20 magnitude = ? light years?

Are you asking about using a telescope in a dark dry location with your eyes to barely view the brightest known object at any given distance? or are you asking what is required to get a good look at the shape of the galaxies at some specific distance?

Or perhaps you are asking about being able to record such images with a really good expensive camera?

Just as a reference, I don't recall ever seeing a z=2 galaxy imaged by the 5 meter telescope on Mount Palomar. That thing was pretty expensive, and unless you're someone very wealthy, I'm guessing it is outside your budget.

keta
2006-Apr-09, 10:48 PM
the 20" telescope wit the magnitude of 20 has a redshift of 2 , and the 17.5 magnitude telescope is a 12" big differnce in size and portablity soo wat im asking is , about how far can these telescopes see in light years thats all i wanna soo can someone plz give me a answer :) , red shift is distance magnitude is light , i no that fainter stars aint allways further away but it should still give u a idea of distance.

antoniseb
2006-Apr-09, 11:15 PM
Redshift of z=2 is roughly 10 billion light years.

keta
2006-Apr-09, 11:45 PM
well i doubt a 20" 20 magnitude telescope would see that far but i read on a web site that 20 magnitude was around red shift 2 , thanks for ur reply :) now i just need to find out what those 3 magnitudes really would be around , also im thinking about geting a small portable telescope for now but im researching big telescopes for the reason that when i build my place its going to have its own room and be bolted down soo portablity aint a factor , the biggest telescope i been able to find forsale is 20" do yous no any forsale bigger or places that will build them ? , if so plz link me to a web site :)

aurora
2006-Apr-10, 12:58 AM
the biggest telescope i been able to find forsale is 20" do yous no any forsale bigger or places that will build them ? , if so plz link me to a web site :)

Try Astronomy Mall
http://astronomy-mall.com/

Or Astro Guide
http://www.astronomy.net/astroguide/manufacturer/

Starmaster goes up to 28" http://www.starmastertelescopes.com/
Starsplitter goes up to 30" http://www.starsplitter.com/index1.html

The obsession web site seems to be down today or I would link you to it.

cjl
2006-Apr-10, 03:07 AM
Keep in mind, however, that getting above about 8" begins to get difficult, and the 20" and larger sizes are ridiculously, impractically large. That having been said, they can see a LOT

keta
2006-Apr-10, 03:24 AM
thx aurora :) , and cjl i no thats wat im looking for lol :) like right now im just gnana get a 12" but later on im going to get as big as i can , because i wont have to move it once i get my place :) thats reason im looking now to see wat i can get that aint to expensive :)

ozark1
2006-Apr-27, 12:01 PM
My personal preference is for a quality portable telescope with a CCD camera and laptop. I use an ETX-125 which is just 5" across and yet have successfully imaged down to 17.5. Visually 17.5 would require a 44" monster.

(Note: roughly speaking the Hale has a visual limit 25 times better (5sq) - or about mag 21)

Skyywatcher
2006-May-27, 02:06 AM
Remember what you will see Black and white is the best description. So to be portable sct or a mak up to maybe 8 inches if you have good arms for setting the 8 up. A pal is always a good idea. You will see say 14 ish easily. Caveat look before you buy. Literally

MG1962A
2006-May-27, 02:36 AM
the 20" telescope wit the magnitude of 20 has a redshift of 2 , and the 17.5 magnitude telescope is a 12" big differnce in size and portablity soo wat im asking is , about how far can these telescopes see in light years thats all i wanna soo can someone plz give me a answer , red shift is distance magnitude is light , i no that fainter stars aint allways further away but it should still give u a idea of distance.


I'll give you an example of how hard the question you are asking is. Where I live, I can see the Large Magellenic Cloud with the naked eye - so that means I can see 180,000 Light years without any visual aid.

However I cant see Pluto, which is less than half a light day away. See the problem?

The things to look for are resolution and light gathering power of the scope, they are the key to everything.

astromark
2006-May-27, 03:23 AM
Join a astronomical society. Go to a star party. Talk to the people who know.
You are making a mistake to think bigger is best. I can tell you that a dark dry observing site is more important than the size of your scope. The quality of the optics and eye pieces are where you need to be. Determining the distance you can see is as simple as a 'Starry Night' program away. Your enthusiasm is good to see. Learning your way around the sky is rewarding and you will gain much knowledge from fellows of similar interest. The brightness of objects has little to do with distance as MG1962A has said.
Astronomy is an enormous subject. There is much to learn. Take your time and enjoy the challenge. Many people I know would be very happy with a 12 inch telescope. Most of us have or use much lesser sized scopes and find it still a challenge. Good luck and clear skies to you.

tdvance
2006-May-30, 06:40 PM
Join a astronomical society. Go to a star party. Talk to the people who know.
You are making a mistake to think bigger is best. I can tell you that a dark dry observing site is more important than the size of your scope. The quality of the optics and eye pieces are where you need to be. Determining the distance you can see is as simple as a 'Starry Night' program away. Your enthusiasm is good to see. Learning your way around the sky is rewarding and you will gain much knowledge from fellows of similar interest. The brightness of objects has little to do with distance as MG1962A has said.
Astronomy is an enormous subject. There is much to learn. Take your time and enjoy the challenge. Many people I know would be very happy with a 12 inch telescope. Most of us have or use much lesser sized scopes and find it still a challenge. Good luck and clear skies to you.

Definitely the darkness of the sky is very important--I just went to West Virginia to visit my parents for Memorial Day weekend, and could just see M13 with the unaided eye and averted vision. It was just brilliant in binoculars. Then, I returned to Bowie, MD, just 15 miles from the nation's Capital, and not only was it invisible to the unaided eye, in binoculars it was faint and I had to know where to look. Also, M81 and m82, a couple of galaxies--I forget the distance, but they are farther than Andromeda but not all that far, they were easy to find in binoculars in WV, whereas in Bowie, I can just see M81 on about half the nights, and M82 on a really good night--but only knowing where to look and sitting for some time and waiting for the conditions to be just right for them to appear. Likewise, M51, another galaxy, is easily visible in binoculars in WV, but I almost never can see it in Bowie.

I think going to a star party and asking to look through others' telescopes is a good way to decide what you want. And--try to find the darkest place you can, away from the city lights if possible. You can still see some things in a good scope in an urban area, but not nearly as much as with an average scope on, say, the top of Spruce Knob (http://en.wikipedia.org/wiki/Spruce_Knob) (a place I've never observed from, but I will someday).

Todd