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The Bad Astronomer
2005-Mar-03, 07:37 PM
Astronomers Measure Slowest Motion Across The Sky
(http://www.cfa.harvard.edu/press/pr0507.html)


"A snail crawling on Mars would appear to be moving across the surface more than 100 times faster than the motion we measured for this galaxy," said Mark Reid (Harvard-Smithsonian Center for Astrophysics), a co-author on the paper.


Did I ToSeek ToSeek? 8)

Russ
2005-Mar-03, 07:54 PM
Here is a good chance to educate me. I would have thought that galaxies out at 13 billion LY's would have had a smaller proper motion than M33. Just the shear distance would, I think, make this an axiom.

I mean, 2.4 million LY's anit so far in the grand scheme of things. What am I missing?

Tom Ames
2005-Mar-03, 07:58 PM
I suspect that it's the measurement per se that's interesting, and not the slow proper motion itself.

Bozola
2005-Mar-03, 07:58 PM
Here is a good chance to educate me. I would have thought that galaxies out at 13 billion LY's would have had a smaller proper motion than M33. Just the shear distance would, I think, make this an axiom.

I mean, 2.4 million LY's anit so far in the grand scheme of things. What am I missing?

Yes they have a smaller proper motion; it's just smaller than what can be measured. The article is about making measurements, not proper motion.

They have set a new, lower, detection limit for their instruments.

Russ
2005-Mar-03, 08:29 PM
Tom and Bazola: Thanks for the response. I went back and re-read the article and your interpretation, while no doubt correct, is not what I got from the article. I guess I'll have to blame a reporter who is only partially aware of whince he speaks.

My interpritation is: "Geewhiz, this galaxy is hugely far away and we can measure its' proper motion!" not "Our piddling technology has finally evoloved such that it can measure the proper motion of a galaxy that is very close by on the cosmic scale."

George
2005-Mar-03, 10:55 PM
I wondered the same thing, Russ. Once I saw M33 as the galaxy, I realized I should read it closer. :)

It is amazing to see such precision.

I just read that helioseismology can measure solar velocites to as little as 2 mm/sec.

Squink
2005-Mar-04, 01:11 AM
30 microarcseconds per year at a distance of 2.4 million LY works out to a speed of about 1046 kps.

dgavin
2005-Mar-04, 01:41 AM
Astronomers Measure Slowest Motion Across The Sky
(http://www.cfa.harvard.edu/press/pr0507.html)


"A snail crawling on Mars would appear to be moving across the surface more than 100 times faster than the motion we measured for this galaxy," said Mark Reid (Harvard-Smithsonian Center for Astrophysics), a co-author on the paper.


Did I ToSeek ToSeek? 8)

So where is the picture of this snail on mars? Maybe we should send a probe with a cargo carrier to return it to earth. Maybe call it the S-Cargo Mission.

*runs away before being bapped*

A Thousand Pardons
2005-Mar-04, 03:41 PM
Did I ToSeek ToSeek?
I think, technically, you do not ToSeek someone if that someone did not post about that subject. Sometimes, even ToSeek is sick and takes a day off. So, you'll only ToSeek ToSeek if ToSeek posts about the Slowest Motions in another thread, but ToSeek has the Search Engine tuned, and usually avoids allowing us little people that small thrill.

Glom
2005-Mar-04, 03:52 PM
If I post this, you can say you ToSeeked me.

Spaceman Spiff
2005-Mar-04, 04:17 PM
The science article can be found here (http://arxiv.org/abs/astro-ph/0503058). It clears up a lot of the questions several of you have.


We measured the angular rotation and proper motion of the Triangulum Galaxy (M33) with the Very Long Baseline Array by observing two H2O masers on opposite sides of the galaxy. By comparing the angular rotation rate with the inclination and rotation speed, we obtained a distance of 730 +/- 168 kiloparsecs. This distance is consistent with the most recent Cepheid distance measurement. M33 is moving with a velocity of 190 +/- 59 km/s relative to the Milky Way. These measurements promise a new method to determine dynamical models for the Local Group and the mass and dark matter halos of M31, M33 and the Milky Way.

What the astronomers measured is the proper motion (i.e., actual across the line of sight) of molecular clouds in the disk of the spiral galaxy M33 (aka the "Whirlpool"). Proper motion usually has units of arcseconds per year, although in this case the units are microarcseconds per year. They measured both their angular motion in the disk and of the galaxy as a whole. So if we also have knowledge of the gas clouds' actual velocity (km/s) in the disk (and we do, coupling the disk's rotation curve with the known disk inclination to the line of sight), we can compute how far away M33 is. This is another form of geometric distance determination, like parallax. They can also use the information to gauge the space velocity of M33, as they say.

Romanus
2005-Mar-04, 06:17 PM
That's epic. 8) I had no idea they had detected the proper motion of any galaxy before, let alone M 33.

Majin Vegeta
2005-Mar-04, 06:47 PM
:o Everyone here is so smart! But one thing, Why couldn't it have been a Snail on earth? Because earth orbits faster than mars? :wink:

A Thousand Pardons
2005-Mar-04, 07:21 PM
If I post this, you can say you ToSeeked me.
No, no, you have to have a link, and so do I.

Eroica
2005-Mar-05, 11:04 AM
Did I ToSeek ToSeek? 8)
No, but you OutToSeeked him! :D