Starship Asterisk*

Airglow Ripples over Tibet

Explanation: Why would the sky look like a giant target? Airglow. Following a giant thunderstorm over Bangladesh in late April, giant circular ripples of glowing air appeared over Tibet, China, as pictured above. The unusual pattern is created by atmospheric gravity waves, waves of alternating air pressure that can grow with height as the air thins, in this case about 90 kilometers up. Unlike auroras powered by collisions with energetic charged particles and seen at high latitudes, airglow is due to chemiluminescence, the production of light in a chemical reaction. More typically seen near the horizon, airglow keeps the night sky from ever being completely dark.

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APOD Robot wrote:The unusual pattern is created by atmospheric gravity waves, waves of alternating air pressure that can grow with height as the air thins, in this case about 90 kilometers up.

I'd never heard of this meaning for the expression "gravity waves" before this. Normally in astronomy when gravity waves are discussed ripples in space-time caused by rapidly orbiting or colliding massive bodies like black holes are involved.

Bruce

BDanielMayfield wrote: I'd never heard of this meaning for the expression "gravity waves" before this. Normally in astronomy when gravity waves are discussed ripples in space-time caused by rapidly orbiting or colliding massive bodies like black holes are involved.

Bruce

Gravitational waves are astronomical. Whilst gravity waves are a form of buoyancy driven (natural convection) flow, where gravity balances the buoyancy forces.

Tibet ,coma,china ...

For some reason I'm more interested in the spooky robots on the ground than the fancy pattern in the sky.

Always an interesting phenomena....

:---[===] *

Nitpicker wrote:

BDanielMayfield wrote: I'd never heard of this meaning for the expression "gravity waves" before this. Normally in astronomy when gravity waves are discussed ripples in space-time caused by rapidly orbiting or colliding massive bodies like black holes are involved.

Bruce

Gravitational waves are astronomical. Whilst gravity waves are a form of buoyancy driven (natural convection) flow, where gravity balances the buoyancy forces.

By looking up precise definitions I see that this distinction you point out is correct. Thanks.

It is offensive to many people when you refer to this location as Tibet, China. Please do not parade your knowledge of science while revealing your lack of knowledge of history.

betacygnus wrote:It is offensive to many people when you refer to this location as Tibet, China. Please do not parade your knowledge of science while revealing your lack of knowledge of history.

I'm also surprised by this oversight, I've always thought of Tibet as a separate country to China.

betacygnus wrote:It is offensive to many people when you refer to this location as Tibet, China. Please do not parade your knowledge of science while revealing your lack of knowledge of history.

No man is an island.

betacygnus wrote:It is offensive to many people when you refer to this location as Tibet, China. Please do not parade your knowledge of science while revealing your lack of knowledge of history.

It's not quite that simple. Like many ancient lands, the borders of what we call Tibet were not intitially well defined, and have fluctuated over the centuries with the ebb and flow of economic and political power. Traditional lands associated with the Tibetan people (and several other ethnic groups) include areas now claimed by China and India. "Modern" Tibet's borders were only established in the 18th century, and it was more or less independant (and included some traditional Chinese lands) from about 1912 to 1951, when it was invaded by the Chinese Red Army. No part of that Tibet has been an independant nation, like it or not, since 1951. One sect of Bhuddism has done a good job of keeping the idea of an independant Tibet alive, but it is, at its root, a religious desire, not a legal or national one.

Rob

Tibet is a country in an of itself. It is NOT a part of China! It was invaded by China in 1950, proving that "might makes right." The rest of the world has done nothing about it because Tibet has no natural resources, like oil, that the rest of the world covets. Yet Tibet does have something the world needs, but the rest of the world is too ignorant to realize the fact that Tibetan Buddhism is better than anything like oil.
FREE TIBET!

APOD does not create policy itself and goes by the policy of the USA by default. The USA, to my knowledge, right or wrong, recognizes TIbet as part of China. People who have a problem with this should take it up with the USA's Department of State, which does set policy. Politics are not usually debated on APOD as it is a science site. The rules of posting are given here: http://asterisk.apod.com/viewtopic.php?f=28&t=26696 . Further debate on this topic will not be tolerated.

- RJN

I think one very visible object worth mentioning is the globular cluster, Omega Centauri. It is the bright spot left of center.

alter-ego wrote:I think one very visible object worth mentioning is the globular cluster, Omega Centauri. It is the bright spot left of center.

Well spotted, alter-ego.

To the eye, Omega Centauri would look considerably fainter than many of the stars here. But the stars are point sources, and Omega Centauri is an extended source, so the camera makes the distant cluster look brighter than the nearby stars.

Ann

Ann wrote:

alter-ego wrote:I think one very visible object worth mentioning is the globular cluster, Omega Centauri. It is the bright spot left of center.

Well spotted, alter-ego.

To the eye, Omega Centauri would look considerably fainter than many of the stars here. But the stars are point sources, and Omega Centauri is an extended source, so the camera makes the distant cluster look brighter than the nearby stars.

Ann

I would have said that the camera makes all the point sources look larger than they are. But Omega Centauri has an angular size similar to a full moon, and so it appears in this APOD, smaller than it is. To unaided eyes in a darkish sky, Omega Centauri is quite faint and a bit fuzzy, indicative of the fact that it is not a single star or point source of light. The Orion Nebula is a bit similar to my unaided eyes, though it appears larger and brighter. (I suspect that the fact I know what they look like through a longer lens, "helps" my unaided eyes with these observations.)

Nitpicker wrote: ... But Omega Centauri has an angular size similar to a full moon, and so it appears in this APOD, smaller than it is. To unaided eyes in a darkish sky, Omega Centauri is quite faint and a bit fuzzy, indicative of the fact that it is not a single star or point source of light.

At first glance Omeg Cen. does appear smallish, but scaling it's size to the ~53° horizontal FoV, it measures ~½°.

On a side note, I was well outside Melbourne for two nights when Halley swung by. I remember the immense beauty of the Milky Way. The first-ever feeling that we lived truly in the outskirts of a galaxy. The Coal Sack stuck out like as if it was a cloud that was in my way, and, of course the Magellanic Clouds. I really enjoyed that trip with my telescope. The one thing, the ONE THING I regret not ever looking at was Omega Cen. I can't believe I didn't see it, or that I didn't put it on my list!!

I think that was a clear case of tunnel vision.

Hmmm, that's a surprise. I just counted 9 pixels across Omega Cen at this APOD's scale of ~18 pixels per degree. You're quite right (again). It certainly appears a bit smaller than it is, in my wide-angle subs (but that's not saying much).

Nitpicker wrote:Hmmm, that's a surprise. I just counted 9 pixels across Omega Cen at this APOD's scale of ~18 pixels per degree. You're quite right (again). It certainly appears smaller in my wide-angle images (but that's not saying much).

Well, don't de-rate your photos so fast. My quick assessment reveals the APOD magnitude limit (extincted) ≈11, and my similar pixel measurement encompassed some (but not all) the fuzzy perimeter.

You may very well have some nice pictures with a brighter magnitude limit. Keep your results and expectations in line with your experience and equipment. Oh, and of course, don't forget: location, location, location!

Oh, I love my own images, but mainly because of the pleasure in taking and making them simply, with nowhere near the extraordinary effort of most APOD image makers. I am too cheap and impatient to want any more from myself.

My best comparable shot of Omega Cen is here (in reduced form):
http://asterisk.apod.com/download/file. ... &mode=view
from:
http://asterisk.apod.com/viewtopic.php? ... 92#p228792

... and on re-measuring, Omega Cen is almost 0.5°, even without any intensity curve stretching. So there you go, I've surprised myself again.

Nitpicker wrote:Oh, I love my own images, but mainly because of the pleasure in taking and making them simply, with nowhere near the extraordinary effort of most APOD image makers. I am too cheap and impatient to want any more from myself.

My best comparable shot of Omega Cen is here (in reduced form):
http://asterisk.apod.com/download/file. ... &mode=view
from:
http://asterisk.apod.com/viewtopic.php? ... 92#p228792

... and on re-measuring, Omega Cen is almost 0.5°, even without any intensity curve stretching. So there you go, I've surprised myself again.

Yup. So there you go.
I was wondering if you had ever made such measurements on your own images.
Very nice, by the way!

alter-ego wrote:

Nitpicker wrote: ... But Omega Centauri has an angular size similar to a full moon, and so it appears in this APOD, smaller than it is. To unaided eyes in a darkish sky, Omega Centauri is quite faint and a bit fuzzy, indicative of the fact that it is not a single star or point source of light.

The one thing, the ONE THING I regret not ever looking at was Omega Cen. I can't believe I didn't see it, or that I didn't put it on my list!!

Don't forget 47 Tucanae near the SMC, this is possibly the greatest globular cluster in the sky! I get the impression that Omega Centauri is the remnant core of a satellite galaxy.

What are the colorful objects in the foreground?

RJ Emery wrote:What are the colorful objects in the foreground?

Looks like telescopes illuminated by red night lighting.

FYI: http://www.pnas.org/content/112/49.cover-expansion