Starship Asterisk*

Chris Peterson wrote: ↑Wed May 22, 2024 2:51 pm

Ann wrote: ↑Wed May 22, 2024 2:24 pm It seems obvious to me that it is harder to create a blue nitrogen aurora than a green or a red oxygen one. Since the blue aurora is so rare, it has to require a lot of energy to create it. But in the many pictures of auroras that have been submitted to Starship Asterisk* and other sites from the latest solar storm, there have indeed been auroras that have also contained the color blue. That makes sense, if we consider that the latest solar storm was a particularly violent one.

Keep in mind that very few of the aurora pictures we see look like what we see with our eyes. As with most astronomical images, a camera captures much more detail and color than our eyes are capable of. The blue color of auroras is not very bright, and is in a part of the spectrum where our visual sensitivity is very low. So it will show up in images where nothing is visually evident at all. (This is also true of red and green in auroras... at my low latitude, I've captured auroras on camera that were completely invisible to the eye except for a slight colorless sky glow that could come from a variety of sources.)

Roy wrote: ↑Wed May 22, 2024 5:50 pm Thanks for that reference, Ann. It makes it very clear what is thought to happen. Do we know of any experiments to replicate this? Maybe when neon signs were being invented?i
Speaking of seeing auroras at low latitude, I did see the 1989 event, living then in Massachusetts near Boston, about 41 degrees N latitude ( I’m now in Maine, 45 degrees N lat.).

Ann wrote: ↑Wed May 22, 2024 2:24 pm It seems obvious to me that it is harder to create a blue nitrogen aurora than a green or a red oxygen one. Since the blue aurora is so rare, it has to require a lot of energy to create it. But in the many pictures of auroras that have been submitted to Starship Asterisk* and other sites from the latest solar storm, there have indeed been auroras that have also contained the color blue. That makes sense, if we consider that the latest solar storm was a particularly violent one.

Roy wrote: ↑Wed May 22, 2024 1:40 pm I’m having a hard time finding a coherent explanation of what causes the different colors. O2 molecules split because of ultraviolet light, then the O atom picks up an “ambient” electron, (not from the sun , only “particles” come from the sun, not protons and electrons) causing emission of green light or red light, depending on the altitude? And what about N2 and argon molecules?

The color of the aurora depends on the wavelength of the light emitted. This is determined by the specific atmospheric gas and its electrical state, and the energy of the particle that hits the atmospheric gas. The atmosphere consists mainly of nitrogen and oxygen, which emit the characteristic colors of their respective line spectra. Atomic oxygen is responsible for the two main colors of green (wavelength of 557.7 nm) and red (630.0 nm). Nitrogen causes blue and deep red hues.

The strong, green light originates at altitudes of 120 to 180 km. Red Northern Lights occur at even higher altitudes, while blue and violet occur mostly below 120 km. When the sun is "stormy," red colors occur at altitudes of 90 to 100 km.

Roy wrote: ↑Wed May 22, 2024 1:40 pm I’m having a hard time finding a coherent explanation of what causes the different colors. O2 molecules split because of ultraviolet light, then the O atom picks up an “ambient” electron, (not from the sun , only “particles” come from the sun, not protons and electrons) causing emission of green light or red light, depending on the altitude? And what about N2 and argon molecules?