calling all astrophysists..

Fri Sep 05, 2003 11:35 am by kimk

i was just reading up the doppler effect and the theory about colours being related to temperature of a body. consider this senario;
a star is moving *away* from an observer, at a very fast speed, doesn't matter how fast, fast enough for doppler to kick in, that results in reddening of the star.

the temperature of the star is 4000Kelvins, resulting in a reddish colour. then, for the professional astronomer that wants to work out whether the star is moving away from us, moving at same velocity to us, and the temperature, how is he supposed to figure this out just by looking at the star? the star is red. assuming this star is newly found, and no data is available about it, how is the guy supposed to know whether the red is influenced by the temperature or doppler effect? it could be that the star is red and its moving at same velocity to him in space. then again the star could be a young 600kelvins and is moving away, resulting in doppler effect of it becoming red.

so enlighten me.

da astronomer

oh and EDIT:

OWL for HP and astronomy fans alike

Edited by - kimk on 05-09-2003 14:23:57

Fri Sep 05, 2003 12:10 pm by freighter fighter

im no astrophysicist, but red is cold and blue is hot when dealing with space. and incedentaly, space is off white, not black. look it up if u dont belive me

Fri Sep 05, 2003 12:36 pm by kimk

off white?/ not that i don't believe you, but care to elaborate/explain how this comes about?? its interesting ya know.

Fri Sep 05, 2003 1:15 pm by freighter fighter

look here

Edited by - freighter fighter on 05-09-2003 14:15:15

Fri Sep 05, 2003 9:23 pm by richard_s

Stars/galaxies etc do not change colour with velocity. The red and blue due to doppler effect on the emitted light refers to the spectral shift either toward the red end of the spectrum or the blue end . To the naked eye the objects colour does not alter. For example, if a star was emitting a strong band of light in the ultraviolet range, at say 340nm, then the doppler effect would shift that to say 360nm in a redshift and to 320nm in a blue shift. Still UV, but a slightly different wavelength.

Astronomers look for a spectral signature of common atoms like hydrogen or helium. We know what wavelengths of light are associated with these atoms, so if in the example you quoted, the Red Star has a hydrogen spectra that is shifted toward the red end of the spectra even by only a few nm, then it is redshifted.

Edited by - richard_s on 05-09-2003 22:33:15

Fri Sep 05, 2003 9:25 pm by Tawakalna

didn't we do this last week? at some length?

Sat Sep 06, 2003 12:21 am by freighter fighter

we do this everyweek, like some weird groundhog day thing

Sat Sep 06, 2003 3:05 am by kimk

@tawa, yea, we did do the ly-clear last week.

Sat Sep 06, 2003 4:21 am by Wolf_Demon

space is basically NOTHING filled with tons and tons of NOTHINGNESS.

planets r smaller than grains of very fine sand to the universe

so therefore it is filled with asolutley NOTHING

there is asolutely no color. its whatever the human eye sees that we think it looks like.
no1 or anything can explain to the fullest extent of what space is.

May the force be with you, for me, to poop on.

Sat Sep 06, 2003 5:46 am by kimk

@wolf, we were discussing the doppler effect and its influence on the colour of a star in comparison to the temperature of the body, not the colour of the universe. frankly speaking, the universe IMO is black in colour, but filled with other waves of the electromagnetic spectrum because the visible spectrum is so much smaller than say. infra-red spectrum and such. so its black, or invisible, since no waves of the visible spectrum is present to us, i.e. our eyes don't pick up radiowaves - that'll be scary.

Sat Sep 06, 2003 7:29 pm by Setsuna

You rang....?

A star's colour depends on its temperature and it's chemical composition. So if you want to check whether you're seeing a star's true colour, check it's apsorbtion specters to look for characteristic ions/molecules, and you'll know.
Any questions?

Careful what you wish... You might just get it.

Sat Sep 06, 2003 7:56 pm by Tawakalna

lol kimk u r a bad man

Sat Sep 06, 2003 8:33 pm by kimk

i am aint i?
and thnx chetnik, tho that didn't answer my question throughly. but nvm. i read the answer up. seems the doppler doesn't have a visible effect, just trace effects of about 100nms.

Sat Sep 06, 2003 8:49 pm by Gung_Ho

yeah Richard_s had the answer.

On the other hand, if the velocital difference were great enough, I suppose the wave compression and (thus) spectra deviation would be much greater.. It's just that this usually seems not to be the case.

Sun Sep 07, 2003 7:54 am by kimk

yea, i gathered that. but you could get a colour difference with just about 300nm of compression/depression of wavelengths.

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