Here is a photo of Comet Lovejoy taken from orbit.

lovejoy https://spaceflight.nasa.gov/gallery/images/station/crew-30/html/iss030e015472.html

The atmosphere has 3 bands. The lowest is deep blue and so I imagine that is Rayleigh scattering, the same as what makes the sky blue.

I am stumped by the red and green/yellow bands. They are so discrete it seems like some rainbow like refraction but they are in the wrong order.

Why does the Earth's atmosphere have these bands?


1 Answer 1


The upper two colours, that's an ionospheric phenomenon called Airglow which is photoluminescence from various oxygenated ions coming from the dayside of the planet.

Those 'various ions' are only produced in sunlight in the ionosphere. There is some transport of those ions to the nightside of the planet in the ionosphere, and that's how it is possible to see relatively intense colours like in your linked picture.

I'm not sure whether the lower coloured band is in fact Rayleigh-scattering.

  • $\begingroup$ Nice! And there is comet Lovejoy in the Wikipedia article too. But why would airglow look sharply layered? I would think the phenomenon would be pretty diffuse. $\endgroup$
    – Willk
    May 14, 2019 at 21:31
  • 1
    $\begingroup$ @Willk: There are three details to this: 1.)The phenomenon is related to the thickness of the Chapman layer of the ions, which is given by the penetration depth of UV radiation ionizing them. This is an exp-exp function, so relatively steep, giving airglow a layer-like nature. 2.) Ions drift and diffuse east-west due to various plasma phenomena, but I don't think this is what one sees. 3.) Limb viewing geometry. So 1.) and 3.) together give the layering that one sees. $\endgroup$ May 14, 2019 at 23:39

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