How is redshift measured?

How do we know what the frequency should have been?

Dark absorption lines in spectra always appear at particular wavelengths
depending on the elements or compounds that caused them. So it's a simple
matter of comparing laboratory results with what's seen in distant galaxies.

http://imagine.gsfc.nasa.gov/YBA/M31...edshift-2.html


"AngleWyrm" wrote in message
news:9RgOb.88509$na.48706@attbi_s04...
How do we know what the frequency should have been?

the accepted reasoning behind Redshift is that the object emitting the light
is receding from us - which is the reasoning behind an expanding universe.
Has anyone ever tried to come up with an alternate explanation? such as the
light passing through gravity wells, intergalactic material, etc?

--
In GOD We Trust

9/11/2001
Lest we forget

"Ed and Kathy Hannig" wrote in alt.astronomy:

the accepted reasoning behind Redshift is that the object emitting the
light is receding from us - which is the reasoning behind an expanding
universe. Has anyone ever tried to come up with an alternate
explanation? such as the light passing through gravity wells,
intergalactic material, etc?


The Doppler effect is not much of a discussion point. But Halton Arp was
one of the most staunch defenders that the redshift wasn't caused by
expansion of the universe, but by galaxies connected to each other and
being ejected from each other.

http://www.haltonarp.com/

--
CeeBee


"I am not a crook"

"Ed and Kathy Hannig" wrote in message
. com...
the accepted reasoning behind Redshift is that the object emitting the
light
is receding from us - which is the reasoning behind an expanding universe.
Has anyone ever tried to come up with an alternate explanation? such as
the
light passing through gravity wells, intergalactic material, etc?

There's always some new theory strong in words and short in math. Expansion
is the best answer. The absorbtion lines show where the color is and we can
compare that to where it is. Nothing else clearly explains the difference.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

************************************



--
In GOD We Trust

9/11/2001
Lest we forget

Different elements absorb light at particular frequencies and at known intervals
or spacing. If light from a distant star has been redshifted, the absorption
lines will appear offset from what would normally be expected for that element.
By comparing the absorption lines from where they should be to where they are,
one can determine very precisely how fast the object in question is speeding
away from an observer.

Kind of like so:

Absorption spectra of element whatever:
|| | |

Absorption spectra redshifted:
|| | |

Notice the spacing is still the same, just the lines are shifted to the left.
(Left in this example being a lower frequency).

Now my question to the rest of the group: gravity has more effect on lower
frequencies, less on higher frequencies. A good example is radio frequencies,
the lower ones follow the curvature of the earth while the higher ones shoot
straight off into space. Wouldn't this also hold true for light, certainly not
as pronounced but still measurable? If so, wouldn't it be possible to determine
if a spectral shift was due to velocity or gravity?

"AngleWyrm" wrote in message
news:9RgOb.88509$na.48706@attbi_s04...
How do we know what the frequency should have been?

AngleWyrm wrote:

How do we know what the frequency should have been?

The spectral lines produced when each type of molecule emits or
absorbs radiation have distinctive patterns. These 'fingerprints' are
observed both in laboratories on earth and in the spectra of objects
in our own galaxy and its neighbours, so to all appearances they are
the same everywhere; moreover they can be predicted or 'derived from
first principles' by quantum mechanics. So once a distinctive pattern
of lines is recognized in the spectrum of a distant galaxy, it's
quite straightforward to measure its offset from the reference position.

--
Odysseus

Okay, then considering that light travels as a wave, and waves travel at
different speeds through different mediums (speed of sound through water is
different than it's speed through air (at sea level) and different speeds at
different altitudes) wouldn't it make sense that light traveling through
intergalactic space would have a speed different than when it's traversing a
solar system or a galaxy? Once light encounters one of these 'speed traps'
you wouldn't expect it to speed up again as it re-enters intergalactic
areas, would you?
--

In GOD We Trust

9/11/2001
Lest we forget

"Bill Oertell" wrote in message
...

Now my question to the rest of the group: gravity has more effect on lower
frequencies, less on higher frequencies. A good example is radio
frequencies,
the lower ones follow the curvature of the earth while the higher ones
shoot
straight off into space.

I'm pretty certain that's not a gravitational effect. I believe it's due to
diffraction allowing the longer wavelengths of low frequency radio to follow
the curve of the Earth's surface.

Didn't I read something within the past several years about light being
affected by the sun's gravity? And if I'm not mistaken there are instances
of galaxies being magnified due to gravitational lens in space.

--
In GOD We Trust

9/11/2001
Lest we forget