Starship Asterisk*

Rainbow Airglow over the Azores

Explanation: Why would the sky glow like a giant repeating rainbow? Airglow. Now air glows all of the time, but it is usually hard to see. A disturbance however -- like an approaching storm -- may cause noticeable rippling in the Earth's atmosphere. These gravity waves are oscillations in air analogous to those created when a rock is thrown in calm water. The long-duration exposure nearly along the vertical walls of airglow likely made the undulating structure particularly visible. OK, but where do the colors originate? The deep red glow likely originates from OH molecules about 87-kilometers high, excited by ultraviolet light from the Sun. The orange and green airglow is likely caused by sodium and oxygen atoms slightly higher up. The featured image was captured during a climb up Mount Pico in the Azores of Portugal. Ground lights originate from the island of Faial in the Atlantic Ocean. A spectacular sky is visible through this banded airglow, with the central band of our Milky Way Galaxy running up the image center, and M31, the Andromeda Galaxy, visible near the top left.

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Cepheus?

Ok, so what is the difference between atmospheric 'gravity waves' and atmospheric turbulence?

Guest wrote:Cepheus?

Yes, not Ceteus (a possible father of Callisto), nor Cetus (the sea monster to which Cepheus tried to sacrifice his daughter, Andromeda).

Cepheus or Cetus -- I wonder who was feared more by Andromeda?

Gravity waves in the atmosphere? If so, these are the slowest and least energetic ever "observed".

Nitpicker wrote:

Guest wrote:Cepheus?

Yes, not Ceteus (a possible father of Callisto), nor Cetus (the sea monster to which Cepheus tried to sacrifice his daughter, Andromeda).

Cepheus or Cetus -- I wonder who was feared more by Andromeda?

astrodave wrote:Gravity waves in the atmosphere? If so, these are the slowest and least energetic ever "observed".

https://en.wikipedia.org/wiki/Gravity_wave wrote:In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium.

This can't be the first time you've heard the same word or phrase used in two quite different ways.

Rob

Guest wrote:Ok, so what is the difference between atmospheric 'gravity waves' and atmospheric turbulence?

From the "gravity wave" link in APOD:

"Gravity wave
From Wikipedia, the free encyclopedia
Not to be confused with gravitational waves."

and continues with a discussion of gravity waves.

brian

Guest wrote:
Ok, so what is the difference between atmospheric 'gravity waves' and atmospheric turbulence?

The ground often get warm enough during the day to make the bottom mile of the atmosphere convectively unstable and truly turbulent.

Other than that the atmosphere (especially the stratosphere) is thermally stable with restoring forces for any vertical disturbances producing gravity wave periods on the order of ~ 6 minutes. (Night-time air may be colder on a mountain top than in the valley below but it is still much warmer [i.e., less dense] than any valley air that decompressively cools to mountain top pressures.)

However, when there is a strong vertical wind shear Bernoulli effect can overwhelm gravitational restoration such that Kelvin–Helmholtz instability generates an unstable "quasi-turbulent" wave that is periodic in space but NOT in time... unless you fly your airplane through it.

Wow!
It would be really nice to see an animation of these, if more pictures were taken... To see their evolution. Personally I find it both "strange" and "amazing" that there appears to be a relation between airglow emission and the position of air within the wave (phase). It would mean that for some reason Oxygen shines in one place, and OH shines on another.. And maybe the yellow looks are just the superposition of red with green as interpreted by the camera color sensor (this assumption is just to simplify the case of imagining that sodium shines on an intermediate place between O and OH). If this is the case, I could more easily imagine O and OH shining at different heights, but the difference in emission intensity still is curious!

Suddenly, I became very curious of the evolution of airglow during the a night, from an all-sky point and as function of local solar time!...
In other words this is an inspiring picture!

I must move there and contemplate how to explain black holes to myself. And have an ice cold one

Amazing.... should we...WAVE back???

:---[===] *

Nitpicker wrote:

Guest wrote:Cepheus?

Cepheus or Cetus -- I wonder who was feared more by Andromeda?

Andromeda had no fear, she was brave!

Boomer12k wrote:
Amazing.... should we...WAVE back???

:---[===] *

Nitpicker wrote:

Guest wrote:
Cepheus?

Yes, not Ceteus (a possible father of Callisto), nor Cetus
(the sea monster to which Cepheus tried to sacrifice his daughter, Andromeda).

• Setting Cetus was satisfied by devouring an Alaskan moondog.

It's amazing to see how many people confuse gravitational waves with atmospheric gravity waves. Not that I understand them to a high degree but I was curious if atmospheric gravity waves present themselves with destructive and constructive interference patterns after looking at today's APOD. Searching the web I ran across many who were equally curious about "gravitational" waves undergoing destructive interference so that some areas in space "have no or less gravity) i.e. Lagrange points as an example of a possible point in space where that was occurring.

Back to gravity waves. I did run across one paper that spoke to atmospheric gravity waves... and interference in its introduction . "…presence of standing waves in the equatorial ionosphere, possibly as a result of interference between waves from two sources…"

Today's image does not interfere with that conjecture.

starsurfer wrote:

Nitpicker wrote:Cepheus or Cetus -- I wonder who was feared more by Andromeda?

Andromeda had no fear, she was brave!

Tis possible that her bravery is a myth.

I suspect that these wonderful colors we see in the resultant photo were wholly invisible to the photographer's naked eye. They were probably too faint to register except upon the time exposure. Thus, the photographer might have just been surprised when he first saw his own photo.