Friday, May 4, 2012

What is Night Glow/Airglow?

What are the different colors in the Atmosphere?
Even on a moonless night, away from any city lights, you can still see your hand.  Where is this light coming from?  Some of the light is from the stars in the Milky Way, but a majority of this light is created from the atmosphere itself.  Yes, the atmosphere creates light!  This is called night glow (AKA: airglow).  A star-filled night sky is 10 times brighter with airglow than without it. 

What causes Night glow?
Daytime UV radiation excites atoms of oxygen and nitrogen atoms/molecules in the thermosphere. These excited atoms and molecules can either return to their ground state (un-excited) and give off a photon in the process or bump into other atoms and molecules and create other molecules via a chemical reaction. The production of hydroxyl radicals (OH), nitric oxide (NO) and molecular oxygen give off light in process known as chemiluminescence.  This is the major component to night glow, and the reason why there is no such thing as a truly dark sky, even on a moonless night.

The "Sodium Layer" is a yellowish layer between 80-105km above the surface of the earth that has a average thickness of around 5km.  Meteors breaking up in the atmosphere (see below) act as the source of sodium for this layer.  Sodium atoms in this layer in an excited state radiate wavelengths ~589nm in the visible spectrum (yellow light).


Atomic Oxygen

The Red layer of night glow is seen at heights of 150-300km above the surface of the earth.  Red emissions are from excited –OH radicals.  OH radicals are created by the combination of ozone and hydrogen.

As seen in image below, there are non-uniformities, which can be caused by gravity waves.  Similar to how you can cause waves between two adjacent mediums of differing densities (on the surface of a lake at the interface between the denser water and the less dense air), gravity allows for ripples to form between atmospheric layers and thus supports these non-uniformities.


The green light given off is due to the combining of molecular oxygen and molecular nitrogen, at heights around 90-100 km from the surface of the earth, and excited oxygen. When oxygen and nitrogen combine, they form NO (nitric oxide), in a process that emits a photon typically ~558nm (Green). 

The weak blue light is formed by excitation of molecular oxygen and can be seen at ~95km.

Airglow Light Wavelengths


  1. Loved this post! Clear, concise explanation of a wonderful topic. Airglow is one of those phenomena people tend not to be aware of until it is pointed out to them. I knew of it, but thoroughly enjoyed learning the details of how it is generated. Thank you, Alex! (And your profile picture makes me smile every time I see it!)
    (And congrats on publication in Science!!)

  2. This comment has been removed by a blog administrator.

  3. Hello Alex,
    As an astrophotographer, I've often noticed that airglow near the ocean tends to be green while airglow over land tends to be orange/red. Is there a reason for this or is it just coincidence that I have captured airglow in this pattern? I thought perhaps it had to do with evaporation over the ocean making the air more moist......but I'm not the scientist here :)

  4. That is really good and informative post, anyone with the interest in space sciences, need to read this blog and get as much information as they can.

  5. Thank you for this valuable information, I hope it is okay that I bookmarked your website for further references.

    flat earth map

  6. Heavy kitchen cleansing involves cleaning of areas of the commercial kitchen area, including the actual ceiling, flooring, equipment, planning tables as well as walls. The particular focus of this kind of kitchen cleaning would be to get in touch with areas which are out associated with reach throughout regular upkeep drills. deep cleaning services

  7. I was searching some thing relevant to this, And i am feeling lucky, as its the perfect one for what i am looking for.
    Here we can also have all the information about AC maintenance dubai

  8. Oooo, I am just looking for a good and aesthetic straightener. cleaning services in dubai

  9. Truly, this article is really one of the very best in the history of articles
    public communication dubai

  10. I see so many articles with poorly written content that this one is refreshing. It’s great to know there are people that can write well and get their point across. Keep it up
    seo dubai

  11. Thanks for sharing a nice post with us. Keep posting informative piece of writing.
    SEO Dubai

  12. This post could be really enjoyable for the ones who are interested in science and space articles. I enjoyed it too. Thanks for sharing!
    Web design Dubai