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APOD:Aurora Slathers Up the Sky
Image Credit: Jack Fischer, Expedition 52, NASA

Explanation: Like salsa verde on your favorite burrito, a green aurora slathers up the sky in this 2017 June 25 snapshot from the International Space Station. About 400 kilometers (250 miles) above Earth, the orbiting station is itself within the upper realm of the auroral displays. Aurorae have the signature colors of excited molecules and atoms at the low densities found at extreme altitudes. Emission from atomic oxygen dominates this view. The tantalizing glow is green at lower altitudes, but rarer reddish bands extend above the space station's horizon. The orbital scene was captured while passing over a point south and east of Australia, with stars above the horizon at the right belonging to the constellation Canis Major, Orion's big dog. Sirius, alpha star of Canis Major, is the brightest star near the Earth's limb.

APOD:Moon Phases in 2021
Video Credit: Data: Lunar Reconnaissance Orbiter ; Animation: NASA's Scientific Visualization Studio; Music: Brandenburg Concerto No4-1 BWV1049 (Johann Sebastian Bach), by Kevin MacLeod via Incompetech

Explanation: What will the Moon phase be on your birthday this year? It is hard to predict because the Moon's appearance changes nightly. As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The featured video animates images taken by NASA's Moon-orbiting Lunar Reconnaissance Orbiter to show all 12 lunations that appear this year, 2021. A single lunation describes one full cycle of our Moon, including all of its phases. A full lunation takes about 29.5 days, just under a month (moon-th). As each lunation progresses, sunlight reflects from the Moon at different angles, and so illuminates different features differently. During all of this, of course, the Moon always keeps the same face toward the Earth. What is less apparent night-to-night is that the Moon's apparent size changes slightly, and that a slight wobble called a libration occurs as the Moon progresses along its elliptical orbit.

APOD:A Historic Brazilian Constellation
Image Credit & Copyright: Rodrigo Guerra

Explanation: The night sky is filled with stories. Cultures throughout history have projected some of their most enduring legends onto the stars above. Generations of people see these stellar constellations, hear the associated stories, and pass them down. Featured here is the perhaps unfamiliar constellation of the Old Man, long recognized by the Tupi peoples native to regions of South America now known as Brazil. The Old Man, in more modern vernacular, may be composed of the Hyades star cluster as his head and the belt of Orion as part of one leg. Tupi folklore relates that the other leg was cut off by his unhappy wife, causing it to end at the orange star now known as Betelgeuse. The Pleiades star cluster, on the far left, can be interpreted as a head feather. In the featured image, the hobbled Old Man is mirrored by a person posing in the foreground. Folklore of the night sky is important for many reasons, including that it records cultural heritage and documents the universality of human intelligence and imagination.

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