Starship Asterisk*

Airglow Borealis

Explanation: The best known asterism in northern skies hangs over the Canadian Rockies in this mountain and night skyscape taken last week from Banff National Park. But most remarkable is the amazing greenish airglow. With airglow visible to the eye, but not in color, the scene was captured in two exposures with a single camera, one exposure made while tracking the stars and one fixed to a tripod. Airglow emission is predominately from atmospheric oxygen atoms at extremely low densities. Commonly recorded in color by sensitive digital cameras the eerie, diffuse light is seen here in waves across the northern night. Originating at an altitude similar to aurorae, the luminous airglow is due to chemiluminescence, the production of light through chemical excitation and radiative decay. Energy for the chemical excitation is provided during daytime by the Sun's extreme ultraviolet radiation. Unlike aurorae which are limited to high latitudes, airglow can be found around the globe.

<< Previous APOD

This Day in APOD

Next APOD >>

A couple of the links went into more detail (at a level we novices can understand) about gravity waves in the atmosphere. The source of the disturbances that produced these waves that then had such wide ranging effect upon our atmosphere made me wonder what would be the effects, if any, upon the general molecular make up of a galaxy by a supernova, the rock in the pond. Is there really any impact beyond a light year or so by the explosion? What forms of radiation are having what types of impact at what distances? Obviously we can see the radiation in the visible range.

NCTom wrote: ↑Sat Oct 27, 2018 11:27 am A couple of the links went into more detail (at a level we novices can understand) about gravity waves in the atmosphere. The source of the disturbances that produced these waves that then had such wide ranging effect upon our atmosphere made me wonder what would be the effects, if any, upon the general molecular make up of a galaxy by a supernova, the rock in the pond. Is there really any impact beyond a light year or so by the explosion? What forms of radiation are having what types of impact at what distances? Obviously we can see the radiation in the visible range.

I think you may be confusing gravitational waves, which are produced by moving masses (with measurable gravitational waves being produced by the collision of black holes and neutron stars), with gravity waves, which are a fluid dynamic effect. This image shows gravity waves, not gravitational waves.

I'm not sure I understand the description this time. We can see the waves, but not the color? But digital cameras can see the color? So is the color added or is it just a factor of some kind of long exposure? Usually, I follow the explanation with no trouble, but I'll admit to confusion this time around.

E Fish wrote: ↑Sat Oct 27, 2018 1:53 pm I'm not sure I understand the description this time. We can see the waves, but not the color? But digital cameras can see the color? So is the color added or is it just a factor of some kind of long exposure? Usually, I follow the explanation with no trouble, but I'll admit to confusion this time around.

Airglow is bright enough to see with our scotopic (rod) vision, but not our photopic (cone) vision. We don't see color in airglow, just gray. But that means if it has structure in it from gravity waves, we can see that patterning. A camera is much more sensitive than the eye, and is capable of integrating over time, so it readily records the actual color. (The same thing happens with Milky Way shots and dim auroras.)

I know from the explanation and the source (a TWAN photographer) that this not a painting, but it sure looks like one.

Awesome image. (And I don't even like green that much.)

Bruce

Chris Peterson wrote: ↑Sat Oct 27, 2018 2:06 pm Airglow is bright enough to see with our scotopic (rod) vision, but not our photopic (cone) vision. We don't see color in airglow, just gray. But that means if it has structure in it from gravity waves, we can see that patterning. A camera is much more sensitive than the eye, and is capable of integrating over time, so it readily records the actual color. (The same thing happens with Milky Way shots and dim auroras.)

Thank you for the extra explanation. I appreciate it.