APOD: Airglow over Italy (2012 Sep 06)

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APOD: Airglow over Italy (2012 Sep 06)

Post by APOD Robot » Thu Sep 06, 2012 4:06 am

Image Airglow over Italy

Explanation: In this serene night skyscape, the Milky Way's graceful arc stretches over prominent peaks in the Italian Alps known as Tre Cime di Lavaredo. A 180 degree wide-angle panorama made in four exposures on August 24, the scene does look to the north and the sky is suffused with an eerie greenish light. Still, the subtle glowing bands are not aurorae, but airglow. Unlike aurorae 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, and found around the globe. The chemical energy is provided by the Sun's extreme ultraviolet radiation. Like aurorae, the greenish hue of this airglow does originate at altitudes of 100 kilometers or so dominated by emission from excited oxygen atoms. More easily seen near the horizon, airglow keeps the night sky from ever being completely dark.

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by Beyond » Thu Sep 06, 2012 4:21 am

Looks like this is the week of glowing APOD's. Neat-o-rific :!: :!:
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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by Jim Leff » Thu Sep 06, 2012 5:35 am

I think airglow... I am!

MrMcMac

Re: APOD: Airglow over Italy (2012 Sep 06)

Post by MrMcMac » Thu Sep 06, 2012 8:09 am

Airglow? A misnomer? Damn little, if any "air" 100 miles up. Send me up, and I'll check on it for you. :D

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by nstahl » Thu Sep 06, 2012 12:24 pm

If there air going to be more of these I may glow elsewhere.

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by FloridaMike » Thu Sep 06, 2012 12:52 pm

Looks like we are going to have three _glowing_ APOD's in a row this week. Thanks for the introduction to this tenuous topic!
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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by Moonlady » Thu Sep 06, 2012 2:06 pm

Do airglows like this move like aurorae?

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by Chris Peterson » Thu Sep 06, 2012 2:54 pm

Moonlady wrote:Do airglows like this move like aurorae?
No. Since they aren't driven by streams of charged particles, but by electrochemical processes in large volumes of air, they are quite stable compared with auroras. Shifts in brightness normally occur over hours, not minutes or seconds.
Chris

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M102

Re: APOD: Airglow over Italy (2012 Sep 06)

Post by M102 » Thu Sep 06, 2012 3:16 pm

The airglow is probably caused by some anomaly in earth's core. I saw this once in a movie. All we need is some unobtainium and some B-list actors willing to risk their careers and everything will be fine.

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by neufer » Thu Sep 06, 2012 3:21 pm

M102 wrote:
The airglow is probably caused by some anomaly in earth's core. I saw this once in a movie.

All we need is some unobtainium and some B-list actors willing to risk their careers and everything will be fine.
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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by Fuzz Nutz » Thu Sep 06, 2012 3:52 pm

neufer wrote: Where's Ronald Reagan when you need him?
Last seen with his Mommy.

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by Flow Motion » Thu Sep 06, 2012 4:04 pm

I've never heard the term 'airglow' before this week. Is it a phenomenon like noctilucent clouds which is recently discovered and a possible result of global climate change?

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by Chris Peterson » Thu Sep 06, 2012 4:19 pm

Flow Motion wrote:I've never heard the term 'airglow' before this week. Is it a phenomenon like noctilucent clouds which is recently discovered and a possible result of global climate change?
No. It's been known about for 150 years, and has been recognized as a primary limitation in ground-based observations for as long as film and electronic imaging has been the main tool of astronomers. Atmospheric changes caused by global warming don't appear to have any effect on the nature of airglow.
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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by emc » Fri Sep 07, 2012 10:18 am

This APOD is another beautiful bridge of science and art!

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by JohnD » Fri Sep 14, 2012 10:23 am

The explanations here and elsewhere say that the airglow is due to a chemical reaction.
The aurora is due to atoms with electrons raised to higher levels that radiate photons as they fall back (yes?).
Both are driven by solar radiation (?)
So both are due to the same cause and effect, but in airglow an interaction between atoms intervenes?
Just to be clear.
John

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by neufer » Fri Sep 14, 2012 3:06 pm

JohnD wrote:
The explanations here and elsewhere say that the airglow is due to a chemical reaction.
The aurora is due to atoms with electrons raised to higher levels that radiate photons as they fall back (yes?).
Both are driven by solar radiation (?)
So both are due to the same cause and effect, but in airglow an interaction between atoms intervenes?
Just to be clear.
Different causes with similar effects (though in different places):
[url]http://en.wikipedia.org/wiki/Airglow#Induced_airglow[/url] wrote:
<<Airglow is caused by various processes in the upper atmosphere, such as
  • 1) the recombination of ions which were photoionized by the sun during the day,
    2) luminescence caused by cosmic rays striking the upper atmosphere, and
    3) chemiluminescence caused mainly by oxygen and nitrogen reacting with hydroxyl ions at heights of a few hundred kilometers.>>
[url]http://en.wikipedia.org/wiki/Aurora_(astronomy)[/url] wrote:
<<An aurora is a natural light display in the sky particularly in the high latitude (Arctic and Antarctic) regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere (thermosphere). The charged particles originate in the magnetosphere and solar wind and, on Earth, are directed by the Earth's magnetic field into the atmosphere.>>
Art Neuendorffer

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Re: APOD: Airglow over Italy (2012 Sep 06)

Post by neufer » Sun Jan 13, 2013 2:36 am

http://earthobservatory.nasa.gov/IOTD/view.php?id=79817 wrote:
Click to view full size image 1 or image 2
<<In April 2012, waves in Earth’s “airglow” spread across the nighttime skies of Texas like ripples in a pond. In this case, the waves were provoked by a massive thunderstorm.

Airglow is a layer of nighttime light emissions caused by chemical reactions high in Earth’s atmosphere. A variety of reactions involving oxygen, sodium, ozone, and nitrogen result in the production of a very faint amount of light. In fact, it’s approximately one billion times fainter than sunlight. This chemiluminescence is similar to the chemical reactions that light up a glow stick or glow-in-the-dark silly putty.

The “day-night band,” of the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured these glowing ripples in the night sky on April 15, 2012 (top image). The day-night band detects lights over a range of wavelengths from green to near-infrared and uses highly sensitive electronics to observe low light signals. (The absolute minimum signals detectable are at the levels of nightglow emission.) The lower image shows the thunderstorm as observed by a thermal infrared band on VIIRS. This thermal band, which is sensitive only to heat emissions (cold clouds appear white), is not sensitive to the subtle visible-light wave structures seen by the day-night band.

Technically speaking, airglow occurs at all times. During the day it is called “dayglow,” at twilight “twilightglow,” and at night “nightglow.” There are slightly different processes taking place in each case, but in the image above the source of light is nightglow.

The strongest nightglow emissions occur mostly in a relatively thin layer of atmosphere between 85 and 95 kilometers (53 and 60 miles) above the Earth’s surface. Little emission occurs below this layer since there’s a higher concentration of molecules, allowing for dissipation of chemical energy (via collisions rather than light production). Likewise, little emission occurs above that layer because the atmospheric density is so low that there are too few light-emitting reactions to yield an appreciable amount of light.

Suomi NPP is in orbit around Earth at 834 kilometers (about 518 miles), well above the nightglow layer. The day-night band imagery contains signals from the upward emission of the nightglow layer and the reflection of the nightglow emissions from clouds and Earth’s surface.

While nightglow is a well-known phenomenon, it is not typically considered by meteorological sensors. In fact, scientists were surprised at Suomi NPP’s ability to detect it. During the satellite’s check-out procedures, scientists thought this light source was a problem with the sensor until they realized that they were seeing the faintest light in the darkness of night.>>
Art Neuendorffer