Redshift = Distance ??

[BL Lacertae]

The max. redshift is 7 (I think so);
If the redshift would be bigger, the object would stay outside the universe (I think so);

So, you can see, there is an equivalence  between the redshift and the distance...

Help me!!

[Hrundi]

Technically redshift can't ever give you a date before the big bang. It is a way to measure distance however, to a certain degree of accuracy.

[Alice]

Redshift is z, isn't it? I've only just realised as a result of reading all these posts, and I keep getting z values of 12 or 14 or 15. Surely something's wrong? I click on it and it tells me "magnitude". But I'm sure I've read that it's z?

[zookeeperKevin]

Redshift is z, isn't it? I've only just realised as a result of reading all these posts, and I keep getting z values of 12 or 14 or 15. Surely something's wrong? I click on it and it tells me "magnitude". But I'm sure I've read that it's z?

That's the z-band magnitude.

If a galaxy has a spectrum, then that number will be far below on the Explorer page as part of the spectrum info.

[Alice]

Oh, right, thanks. 

[suprtrkr]

Redshift is z, isn't it? I've only just realised as a result of reading all these posts, and I keep getting z values of 12 or 14 or 15. Surely something's wrong? I click on it and it tells me "magnitude". But I'm sure I've read that it's z?

Alice, that's luminous z, how bright the object was viewed through the "z" filter. Redshift z, when we have it, appears in the one-line table below the image where the spectrum data is contained. Most of these are <1, although Edd posted a quasar the other day with 6.4 or something. In general, the larger the number the more distant the object is. There is a (lengthy and at times offtop and a little hard to follow) very good thread over in Analysis Tips that will help you understand a little better.

FWIW, here is a calculator to give you a guess at the actual distance in megaparsecs (with a conversion factor for lightyears). Input your z value in the left hand slot, hit "flat" and, per Edd, the "Comoving Radial Distance" is your best guess.

[Hrundi]

No need to read a lengthy thread to understand it. How it works:
Waves from objects moving away from us get shifted towards the red portion of the spectrum. Z is a way to quantify that shift.
The Hubble parameter says that for every Mpc further a thing is, it moves 71km/s faster away from you. This doesn't apply to the local group such as Andromeda though, since that's blueshifted. Anyway according to that the far away objects are distancing themselves from us with incredible speed, which shifts their spectra heavily towards the red, hence high z value.

[zookeeper_anze]

Not that while the relation between redshift and distance is not linear, it is monotonic, i.e. the bigger the redshit, the further away the objects is. But since it is further away, you are also looking at it while the universe was younger. So redshift can also be used to measure *time* with z=0 is now and z -> infinity is approaching big bang. The oldest object are believed to have formed at z around 10-20 and the highest redshift object we have seen is a quasar at something a bit less than z=7... While this record will probably be pushed up, there are simply fewer very bright objects at higher redshift. Cosmic Microwave Background has redshift of about z=1300.

a

[GwydionM]

Redshift is based on how fast the object is moving away from us.  For stars, red-shifts are relatively small, some are coming closer and some moving away. 

In a static universe, that would also be true for galaxies.  But Edwin Hubble (http://en.wikipedia.org/wiki/Edwin_Hubble) found that red-shift got steadily bigger for galaxies that were fainter, and therefore further away.  Finding quasars and similar confirmed this - there were a few suggestions about 'tired light' and similar, but these never convinced many people.

For distant objects, the redshift is entirely caused by distance and by being part of an expanded universe. 

[Nightblizzard]

Not that while the relation between redshift and distance is not linear, it is monotonic, i.e. the bigger the redshit, the further away the objects is. But since it is further away, you are also looking at it while the universe was younger. So redshift can also be used to measure *time* with z=0 is now and z -> infinity is approaching big bang. The oldest object are believed to have formed at z around 10-20 and the highest redshift object we have seen is a quasar at something a bit less than z=7... While this record will probably be pushed up, there are simply fewer very bright objects at higher redshift. Cosmic Microwave Background has redshift of about z=1300.

a

How can you meassure time? It takes 8 minutes for light to reach the earth, yet the sun has a redshift of 0... or.. do you mean that, since the universe is expanding, all object are "moving" away from each other? But then, wouldn't that mean that all galaxies will "die" because of that? The more the stars move away from each other, the less it looks like a galaxy on pictures xP

[Hrundi]

The light from the Sun is from 8 minutes in the past. The light from Proxima Centauri 4.2 years in the past.
The faster an object moves away from you, the higher its Z, and the further away it is from. But at say 5 billion light years distant the light emitted 5 billion years ago is just reaching us. That's why watching further and further in space is also watching the universe in its past.

[pmf71]

Not that while the relation between redshift and distance is not linear, it is monotonic, i.e. the bigger the redshit, the further away the objects is. But since it is further away, you are also looking at it while the universe was younger. So redshift can also be used to measure *time* with z=0 is now and z -> infinity is approaching big bang. The oldest object are believed to have formed at z around 10-20 and the highest redshift object we have seen is a quasar at something a bit less than z=7... While this record will probably be pushed up, there are simply fewer very bright objects at higher redshift. Cosmic Microwave Background has redshift of about z=1300.

a

How can you meassure time? It takes 8 minutes for light to reach the earth, yet the sun has a redshift of 0... or.. do you mean that, since the universe is expanding, all object are "moving" away from each other? But then, wouldn't that mean that all galaxies will "die" because of that? The more the stars move away from each other, the less it looks like a galaxy on pictures xP

Yes our sun has a redshift of 0 (it's neither moving away from us, or getting closer to us), andromeda has a negative redshift, or a blueshift(it's coming toward us, in a few billion years it will merge with our milky way). Our sun, the stars in our milky way, andromeda, and the other galaxies in our local group are the only exceptions to the "rule" of the expanding universe. All galaxies further than our local group are in fact moving away from us. Thus we use redshift to measure their distance.

But we can even calculate how fast the moon is moving away from us by measuring redshift, with really really really really REALLY accurate measuring equipment. But scientists found an easier way, using laser ranging. The moon is receding from us by a little less than 4 centimeters per year, by the way.

[jlowe]

HUBBLEsite Reference Desk's Calaculators & Charts section has Redshift to Time (millions of years/lightyears).. calculator, Distance calculator, Speed.. etc etc..
.. jay

[wandering eye]

I found this page helpful
   http://www.atlasoftheuniverse.com/redshift.html

In the graph below D_T is "the time taken for the light from distant galaxies to reach us".  Go to the above link for explanations of the other variables.

[ubberfish1]

I've read that the hubble telescope has seen seen a galaxy that was so redshifted; that it was nearly impossible to see, but that it is only 700 million years after the radiation barrier or dark ages.