Galaxy Zoo Talk

Redshift - Am I getting this right?

  • Alpha_Aurigae by Alpha_Aurigae

    enter image description here

    http://www.castlerock.wednet.edu/HS/stello/Astronomy/TEXT/CHAISSON/BG316/HTML/MP1601.htm

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  • Budgieye by Budgieye moderator

    It is nearby if you are thinking like a cosmologist or a Zooite who thinks about the whole universe. It is distant for any astronomer who wants a decent image, and who would consider this a distant galaxy.

    First remember that redshift is actually a measure of the expansion of the universe. The further away an object is, the faster it seem to travel away from us as the universe expands.

    "Look back time" gets complicated as you look further back. Each value of redshift gives a distance and time for that galaxy when the light left the galaxy. In the time that the light traveled to us, the universe continued to expand and accelerate. The further away the galaxy is, the more complicated the examples get and the more my head hurts.

    z=.0.010 No quasars. It is so close that there is no change in colour. If a quasar was very close, it would be green on SDSS. But there are no nearby quasars, any green is due to active galaxy nuclei , which are dim compared to quasars. Quasars were active in the distant past, so we don't see any nearby. We see them half way across the universe, because we are looking at them as the light left them billions of years ago.

    z=0.05 1/50th across the universe. .Your quasar, which is not really a powerful quasar, but a Seyfert. The correlation between redshift and distance away is still easy to follow. As the redshift increases, the distance increases. The green colour has been redshifted to red. For your quasar, with z=0.05 http://talk.galaxyzoo.org/#/subjects/AGZ0005bus , it would be 700 million light-years away.

    z=0.173 is the closest "real quasar" PKS2349

    z=0.5 it gets complicated talking about the size of the universe. Present distance is no longer the same as look back time, because as you look back in time, the universe was smaller. So the distances in the two columns don't match up very well. This is when your head starts to hurt.

    z= 1.4 One tenth of the way across the universe. The galaxy is right now travelling away from us at the speed of light. If light left the galaxy at this moment, it would never reach us, because it is outside our event horizon. However, the light left it about 7 billion years ago, so the light has reached us.

    Any yes, light cannot travel faster than the speed of light, but the universe is expanding faster than the speed of light.

    I'm not sure if I answered your question. Have a nice coffee while you ponder.

    Any quasar with z>1 is going away from us in excess of c ? http://www.galaxyzooforum.org/index.php?topic=277872.msg470977#msg470977

    Galaxy Redshift Chart http://talk.galaxyzoo.org/#/boards/BGZ0000001/discussions/DGZ0000ulp?page=2

    Forum: Re: z and velocity of recession by Edd http://www.galaxyzooforum.org/index.php?topic=273059.msg217557#msg217557 "

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  • Alpha_Aurigae by Alpha_Aurigae

    Thanks Budgieye, I am trying to learn about redshift, distances and colours, and your posts here and elsewhere are very helpful esp. the Galaxy Redshift Chart. It is my next step in understanding redshifts, and like you said I need some time to let it all sink in before I drown in the wonders of the universe 😉

    Thanks for answering, much appreciated!!!

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  • Alpha_Aurigae by Alpha_Aurigae

    Going to collect some links to helpful videos:

    Redshift - Sixty Symbols : https://www.youtube.com/watch?v=8U4O8XB14tg

    Redshift and Hubble's Law : https://www.youtube.com/watch?v=Rnu9gJCpf4E

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