During a climb to the highest mountain of Portugal (2351m), Pico mountain, in Pico island - Azores, I stopped at about 1200 meters to appreciate the views and photograph the lights coming from the island of Faial in the middle of the Atlantic Ocean, during the night in a rare occasion with only a few clouds with part of the "winter" Milky Way visible. Above the low clouds, I have captured strange "rainbow bands" of airglow. The bands are actually huge parallel structures in the thermosphere 90 km upwards. Perspective makes them appear to converge. This Gravity Waves* (not confuse with gravitational waves) propagating upwards from disturbances lower down in the atmosphere, are likely the source of the bands. The wave amplitude increases with height (reducing density) and wavelengths can be thousands of kilometers.Airglow is the light of electronically and/or vibration-rotationally excited atoms and molecules high in Earth's atmosphere, by solar ultra-violet radiation. In this image, we can see almost each possible airglow color appearing on a single band. The green airglow is from oxygen atoms (1S ->1D) 90-100 km high. The red/orange could be yet more oxygen airglow, this time from atoms 150-300km high where the atmosphere is so sparse and collisions so infrequent that the atoms have time to radiate 'forbidden' light (1D ->3P) before losing their electronic excitation in impacts with other atoms and molecules. Deep red banded airglow is likely emission from vibrationally excited OH radicals in a layer ~86km high. The bands are caused by gravity waves propagating upwards from the lower atmosphere. They modulate the local pressure, temperature and specie concentrations. Blue airglow is much much fainter and not very obvious on the image. Excited molecular oxygen at ~95 km high can produce it. The excitation is indirect. Possible routes are via daylight dissociation of N2 and NO or twilight recombination of NO+ whose reaction products generate excited O2. The oxygen the

Image Credit & Copyright: Miguel Claro (TWAN); Rollover Annotation: Judy Schmidt

왜 하늘이 무지개 빛으로 아른거리는 것일까? 바로 대기광이다. 매순간 공기는 빛나고 있지만, 그것을 직접 보는 것은 어렵다. 하지만 태풍이 다가올 때와 같이 난류가 일어나면, 지구 대기를 물결치게 만들 수 있다. 이 중력파는 공기를 진동시켜서 이처럼 잔잔한 물가 위에 놓인 암석 위에 아름다운 무늬를 만들었다. 수직으로 뻗은 대기광을 바라보며 장 노출 촬영을 통해 이런 아름다운 모습을 담을 수 있었다. 그렇다면, 이 색깔은 어떻게 만들어진 것일까? 깊은 붉은 빛은 약 87km 높이에 떠있는 OH 분자가 태양에서 날아온 자외선 빛에 의해 에너지를 얻어 빛나는 것이다. 주황빛과 녹색빛의 대기광은 그보다 약간 더 높이 떠있는 나트륨과 산소 원자에서 나오는 것이다. 위의 사진은 포르투갈의 아조레스에 위치한 피코 산을 등반하면서 촬영한 것이다. 대서양에 위치한 파얄 섬의 도시 빛이 아래 빛나고 있다. 물결치는 대기광 사이로 아름다운 밤하늘의 가운데 우리 은하수의 중심부가 그리고 M31, 안드로메다 은하가 왼쪽에 보인다.

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.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
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Translated by: WouldYouLike

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