Friday, November 18, 2016
LITTLE PLANET AIRGLOW Taken by Jeff Dai on October 8, 2016 @ Tibet, China
Earth’s nightside sky is never completely dark. Long after sunset and even with no interference from artificial lights, moonlight or aurorae the sky has a soft glow. Pictured above is a 360-degree stereographic projection showing the night sky of the camping site in the Himalayas on the border of China and Bhutan. The pervasive green and yellowish light is airglow display. Airglow is a weak light emission stemming from the chemical reactions involving oxygen, nitrogen, sodium and ozone(chemiluminescence) at altitudes between about 50 to 60 mi (80 to 96 km) above the Earth’s surface. Unlike the aurora, the airglow is visible all over the globe. Though brightest 10-15 degrees above the horizon it fills the sky. It is strongly coloured yet it is without colour to our unaided eyes because its light is below the threshold of colour perception.
The surrounding sky contains many jewels of the night including the Polaris at 12 pm, the bright band of Zodiacal light and M44 at 3 pm, the plane of our Milky Way galaxy at 4:30 pm and 11pm, M31 at 10 pm. Sirius, the brightest star in earth’s night, is visible at 5 pm. But but really the harder thing to find is Canopus, the second brightest star in the night sky. A full field interactive version of this scene can be found in the attachment.