Comments on: Milk Bar

By: The Milky Way, Defined at Moonage SpaceDream

The Milky Way, Defined at Moonage SpaceDream — Sat, 12 May 2007 03:13:05 +0000

[...] better descriptions and discussion can be found at the Bad Astronomy Blog. Technorati Tags: milky way, The [...]

By: freeza

freeza — Thu, 01 Sep 2005 06:39:16 +0000

how do we know what out galaxy looks like from within it? just wondering.

By: suitti

suitti — Mon, 29 Aug 2005 17:46:15 +0000

If we could only just get â€œsomeoneâ€? from the Andromeda Galaxy to send us a tight laser-beamed digital CCD of the Milky Way!

Let’s say we discover clear signals from ET in M31 today, perhaps via optical laser. Let’s say that we transmit the question right away. Let’s say they get it, figure out what it means,
and send us an image right away. Its going to take 2,250,000 years to get the request there, and another 2,250,000 years to get the answer. So, in 4,500,000 years we’ll get an image that’s 2,250,000 years old. I’d like to be around for the answer. Really, i’ll wait.

Still, the new image would make a better T shirt – You are here.

By: Nigel Depledge

Nigel Depledge — Thu, 25 Aug 2005 21:13:32 +0000

It’s amazing, isn’t it? We can view hundreds of galaxies in one image at about a billion or so parsecs away (e.g. the Hubble Deep Field), yet we are still discovering things about the basic structure of our own galaxy. These things are only 30,000 light years away.

Doesn’t sound like much, when you say it like that, does it? I think it’s around 176 quadrillion miles from here to the galactic centre. Taxi!

Anyway, make mine a single-malt scotch. Something western, but not too vigorous. Say, a 12-year-old Bunnahabhain. Straight up. No ice.

By: Oscar

Oscar — Wed, 24 Aug 2005 17:51:40 +0000

Too bad that guy turned out to be a fraud… I never heard of his name
before.. but then again, I thought that the question of whether gravity
was instantaneous or delayed wasn’t one open for debate as I would
think that it shouldn’t be too hard to calculate if you knew the location
and motion of the objects around you, the amount of redshift, the
earth’s momentum, etc.. surely the answer should be known by now,
or at least one of the possibilities been plausibly ruled out…

By: Irishman

Irishman — Mon, 22 Aug 2005 14:40:03 +0000

BB, please elaborate on where your understanding of projected gravitation derives. It does not jive with my understanding of General Relativity.

By: neutron

neutron — Sat, 20 Aug 2005 00:03:34 +0000

This very article in the JPL website prompted me in my blog to rejoice that we now have somewhere to go for a post-prandial drink after we have eaten in the “Restaurant at the End of the Universe”!
You are doing a great job, Phil, it seems we need every skeptic we can find at the moment.

By: BB

BB — Fri, 19 Aug 2005 12:20:39 +0000

Someone correct me if I’m wrong, but this is what I know about gravity:
According to General Relativity, any body will warp space-time in such a way as to cause surrounding objects to “fall” toward it. For an object which is stationary, the way space-time is warped is relatively simple, and could be imagined to be just like the shape the fabric of a trampoline would make with a bowling ball in it. For an object moving with a constant acceleration, however, spacetime will be warped in such a way that everything surrounding it will always experience a force of gravity toward the point in space that the first object will be by the time the “ripple” reaches it. For example, right now, the earth is pulled toward where the sun is right now because eight minutes ago, the sun caused a distortion in spacetime that, when it reached the earth just now, would cause it to experience a force toward where the sun would be 8 minutes from then (right now.) And right now, the sun is causing a distortion that in 8 minutes will cause the earth to experience a force toward where the sun will be in 8 minutes. I’m not sure if that makes any sense to anyone else, though.

By: P. Edward Murray

P. Edward Murray — Fri, 19 Aug 2005 04:59:23 +0000

VanFlandern is a PhD Astronomer who believes that the
“Face on Mars” is artificial and not natural.

A “fact” that we know now to be untrure it’s natural and more of a product of using less magnification. At higher magnification the “face” turns into a Mesa of hills & valleys.

He used to post regularly on Sci.Astro. Amateur.

Thank God he is gone!

By: Chet Twarog

Chet Twarog — Thu, 18 Aug 2005 15:54:51 +0000

If we could only just get “someone” from the Andromeda Galaxy to send us a tight laser-beamed digital CCD of the Milky Way!

By: Jim

Jim — Thu, 18 Aug 2005 03:51:29 +0000

From what I’ve read, astronomers are pretty sure that there’s a black hole near/at Sagittarius A*, which would account for the “water going down a bathtub drain” look (from above) of our spiral galaxy. I was surprised to read about the bar, though, as I would have thought a black hole would have precluded such a thing.

Oh, I’ll take some Stella Artois in a glass, thanks.

By: kara

kara — Thu, 18 Aug 2005 02:02:00 +0000

I’ll have my shaken – not stirred

By: arensb

arensb — Wed, 17 Aug 2005 21:48:31 +0000

Well, a bit of Googling later, it appears that there is currently no definitive answer on the speed of propagation of gravity. One Sergei Kopeikin has made some observations that he believes show that gravity travels at the speed of light, but other people claim that he’s wrong. AIUI the basic problem is that we don’t have instruments sensitive enough to measure the speed of gravity, at least not with ordinary occurrences like Jupiter passing in front of a quasar.

PS: Phil, do you know about the error messages generated when one submits a comment here?

By: rsgeek

rsgeek — Wed, 17 Aug 2005 20:30:52 +0000

I wouldn’t pay too much attention to VanFlandern — he’s a “fringe” guy. For instance, he apparently thinks Valles Marineris on Mars was created by a crashed (crashing?) moon rolling across the martian surface…

Meanwhile, I can’t recall what Einstein predicted the “speed of gravity” would be, but if memory serves, a number of experiments are planned (or underway) in attempts to measure it.

By: Oscar

Oscar — Wed, 17 Aug 2005 19:02:35 +0000

this was the first useful hit I got on google..

http://www.ldolphin.org/vanFlandern/gravityspeed.html

perhaps you can find the flaw in this guy’s explanation as these
formula’s give me kind of a headache..(math class has been a
long time ago for me )

By: gopher65

gopher65 — Wed, 17 Aug 2005 18:03:51 +0000

IIRC gravity does indeed travel at the speed of light, and the sun does indeed orbit the place where the sun was 8 minutes ago.

By: Oscar

Oscar — Wed, 17 Aug 2005 17:50:00 +0000

>But when youâ€™re dealing with galaxies, Iâ€™m guessing that itâ€™s not safe to ?>assume that gravity is propagated instantaneously. Presumably Sol is >feeling the pull not of the center of the Milky Way where it is today, but >where it was 30,000 years ago.
>
>Am I completely off-base here? And if not, does this have much to do >with the shapes of galaxies, including bars and spiral arms?

If you would see gravity as an effect that operates at light speed…
Gravity has if I’m not mistaken been observed as a distortion in the
fabric of time and space, and not a kind of particle pull subject to
a maximum speed..
The Earth orbits the Sun relative to where the Sun is now, not where
it was eight minutes ago.. correct me if I’m wrong, because I can’t post
any reference at the moment.

By: arensb

arensb — Wed, 17 Aug 2005 17:39:42 +0000

When gravity is taught in physics class, it’s generally assumed that masses act instantaneously upon each other: when an orbiting satellite moves one meter in its orbit, it instantly “knows” the Earth’s new position relative to it, and reacts accordingly. This is good enough for everyday calculations.

But when you’re dealing with galaxies, I’m guessing that it’s not safe to assume that gravity is propagated instantaneously. Presumably Sol is feeling the pull not of the center of the Milky Way where it is today, but where it was 30,000 years ago.

Am I completely off-base here? And if not, does this have much to do with the shapes of galaxies, including bars and spiral arms?

By: Irishman

Irishman — Wed, 17 Aug 2005 14:23:01 +0000

> This is an observatory designed to see infrared light, invisible to the eye. You can think of the light as being redder than red, if that helps.

I’m not sure that explanation actually helps most people. How can something be redder than red? Can something be greener than green? Yes for violet, but not for yellow. What?

Understanding that comment requires understanding looking at visible light as a directional chart, red on one end and violet on the other. Thus there is a “red” direction and a “violet” direction. That is how something can be “redder” than red – it is farther in the red direction of the scale.

That’s not very intuitive, and I don’t think it will make much sense to most people. YMMV.

By: Moonage Spacedream

Moonage Spacedream — Wed, 17 Aug 2005 12:42:39 +0000

The Milky Way, Defined

The Milky Way, due to observations from the Spitzer Space Telescope, is now a more defined. Instead of a flat disk like I’ve always visioned, it’s apparently a disk within a disk. Much better descriptions and discussion can be

By: Michelle Rochon

Michelle Rochon — Wed, 17 Aug 2005 11:53:15 +0000

I always wanted to see our own galaxy for myself… It’s just too bad we can’t go very far away and take a picture! But hey, artist visions are good for that!

Astronomy Picture of the Day already featured an artist vision of the Milky Way too!
http://antwrp.gsfc.nasa.gov/apod/ap050104.html

But the one you posted is much prettier.

By: Outside observer

Outside observer — Wed, 17 Aug 2005 10:31:52 +0000

The large version of that pic is nifty.( http://www.news.wisc.edu/newsphotos/images/Milky_Way_galaxy_sun05.jpg )

Instead of “sun” the sign should have said “You are here”. =D

By: Randall

Randall — Wed, 17 Aug 2005 06:24:50 +0000

Clearly, a better title for this post would have been “Milky Way Bar.”