galactic rotation

RichD

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Apr 16, 2013, 12:45:38 AM4/16/13

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How do astronomers know our galaxy is rotating, how do
they measure the velocity?

And, how do they measure the rotational velocity of other galaxies?

--
Rich

Lord Androcles, Zeroth Earl of Medway

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Apr 16, 2013, 3:17:38 AM4/16/13

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"RichD" wrote in message
news:3ef61007-cf0b-4f64...@ys5g2000pbc.googlegroups.com...

================================================
They don't *know* ours is rotating, but since all other flat galaxies
do it is reasonable that ours should.
Globular galaxies (such as the Magellanic clouds) don't rotate.
They measure rotation by the Doppler shift from one side moving
away and the other side moving toward us.
Because they believe the idiot Einstein they get the right rotation
but the wrong speed and then they invent dork matter to explain it.

-- This message is brought to you from the keyboard of
Lord Androcles, Zeroth Earl of Medway.
When the fools chicken farmer Wilson and Van de faggot present an argument I
cannot laugh at I'll retire from usenet.

George Herold

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Apr 16, 2013, 1:38:00 PM4/16/13

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Well this is mostly speculation... but you can google as well as I
can.

First if our galaxy wasn't rotating then all the stars would fall to
the center.
Second I think we can see the galactic motion as part of the
correction in the CMB.. the proper motion of the earth.

For the other galazies I assume they look at doppler shifts of
spectral lines for stars near the rim... with an edge on galaxy.

George H.

Louis Boyd

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Apr 16, 2013, 1:37:51 PM4/16/13

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Galaxys are not solid disks. From our vantage point within our galaxy
we can observe the differential velocity of stars and gases in the
arms and core using both optical and radio telescopes. So we know the
direction of rotation and the velocity of many parts of our galaxy with
respect to us.

It's relatively easy to measure the rotational velocity of other galaxys
if their axis of rotation isn't pointed directly at at us. Just lay the
slit of a high resolution spectrograph across the long axis of a spiral
or elliptical galaxy and and measure the wavelength shift of the
ionized gases approaching on one side and receding in the other. There
is a V*(sin (i)) correction there i is the angle of tilt of the galaxy
with respect to the viewer. The measurement also shows the mass
distribution as a function of radius from the galaxy's center.

Double-A

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Apr 16, 2013, 2:02:00 PM4/16/13

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By using their extremely sensitive instruments.

Double-A

RichD

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Apr 29, 2013, 2:28:42 PM4/29/13

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On Apr 16, Louis Boyd <b...@apt0.sao.arizona.edu> wrote:
> > And, how do they measure the rotational velocity of other galaxies?
>

> It's relatively easy to measure the rotational velocity of other galaxys
> if their axis of rotation isn't pointed directly at at us. Just lay the
> slit of a high resolution spectrograph across the long axis of a spiral
> or elliptical galaxy and and measure the wavelength shift of the
> ionized gases approaching on one side and receding in the other.

They can resolve individual stars in foreign galaxies?

--
Rich

va_t...@yahoo.com

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May 4, 2013, 9:43:56 AM5/4/13

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From http://www.universetoday.com/23870/the-milky-ways-rotation/

"To determine the rotation rate of the Milky Way, astronomers mapped star forming regions using the Very Long Baseline Array (VLBA) radio telescope. The molecules in these regions amplify naturally occurring radio emissions. By observing how far these regions shifted over time in three dimensions, they were able to calculate the rotation of the entire galactic disk (and figure the mass of the Milky Way, as well)."

also http://arxiv.org/pdf/1209.0759v1.pdf