APOD: The Structured Tails of Comet NEOWISE (2020 Jul 22)
Image Credit & Copyright: Zixuan Lin (Beijing Normal U.) https://apod.nasa.gov/apod/ap200722.html
Explanation: What is creating the structure in Comet NEOWISE's tails? Of the two tails evident, the blue ion tail on the left points directly away from the Sun and is pushed out by the flowing and charged solar wind. Structure in the ion tail comes from different rates of expelled blue-glowing ions from the comet's nucleus, as well as the always complex and continually changing structure of our Sun's wind. Most unusual for Comet C/2020 F3 (NEOWISE), though, is the wavy structure of its dust tail. This dust tail is pushed out by sunlight, but curves as heavier dust particles are better able to resist this light pressure and continue along a solar orbit. Comet NEOWISE's impressive dust-tail striations are not fully understood, as yet, but likely related to rotating streams of sun-reflecting grit liberated by ice melting on its 5-kilometer wide nucleus. The featured 40-image conglomerate, digitally enhanced, was captured three days ago through the dark skies of the Gobi Desert in Inner Mongolia, China. Comet NEOWISE will make it closest pass to the Earth tomorrow as it moves out from the Sun. The comet, already fading but still visible to the unaided eye, should fade more rapidly as it recedes from the Earth.
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APOD: Comet NEOWISE over Lebanon (2020 Jul 07)
Image Credit & Copyright: Maroun Habib (Moophz) https://apod.nasa.gov/apod/ap200707.html
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APOD: Moon Occults Venus (2020 Jun 21)
Image Credit & Copyright: Dzmitry Kananovich https://apod.nasa.gov/apod/ap200621.html
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APOD: NGC 6302: The Butterfly Nebula (2019 Mar 02)
Image Credit: NASA, ESA, Hubble, HLA; Reprocessing & Copyright: Robert Eder https://apod.nasa.gov/apod/ap190302.html
Explanation: The bright clusters and nebulae of planet Earth's night sky are often named for flowers or insects. Though its wingspan covers over 3 light-years, NGC 6302 is no exception. With an estimated surface temperature of about 250,000 degrees C, the dying central star of this particular planetary nebula has become exceptionally hot, shining brightly in ultraviolet light but hidden from direct view by a dense torus of dust. This sharp close-up was recorded by the Hubble Space Telescope in 2009. The Hubble image data is reprocessed here, showing off the remarkable details of the complex planetary nebula. Cutting across a bright cavity of ionized gas, the dust torus surrounding the central star is near the center of this view, almost edge-on to the line-of-sight. Molecular hydrogen has been detected in the hot star's dusty cosmic shroud. NGC 6302 lies about 4,000 light-years away in the arachnologically correct constellation of the Scorpion (Scorpius).
NGC 7293: The Helix Nebula ==
Explanation: A mere seven hundred light years from Earth, in the constellation Aquarius, a sun-like star is dying. Its last few thousand years have produced the Helix Nebula (NGC 7293), a well studied and nearby example of a Planetary Nebula, typical of this final phase of stellar evolution. A total of 28.5 hours of exposure time have gone in to creating this deep view of the nebula. Combining narrow band image data from emission lines of hydrogen atoms in red and oxygen atoms in blue-green hues, it shows remarkable details of the Helix's brighter inner region, about 3 light-years across, but also follows fainter outer halo features that give the nebula a span of well over six light-years. The white dot at the Helix's center is this Planetary Nebula's hot, central star. A simple looking nebula at first glance, the Helix is now understood to have a surprisingly complex geometry.
Satellite Station and Southern Skies (2014 May 31)
APOD: The Cat's Eye Nebula from Hubble
Explanation: To some, it may look like a cat's eye. The alluring Cat's Eye nebula, however, lies three thousand light-years from Earth across interstellar space. A classic planetary nebula, the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Seen so clearly in this digitally reprocessed Hubble Space Telescope image, the truly cosmic eye is over half a light-year across. Of course, gazing into this Cat's Eye, astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.
APOD: Moon, Four Planets, and Emu
Image Credit & Copyright: Alex Cherney (Terrastro, TWAN) https://apod.nasa.gov/apod/ap190208.html
Explanation: A luminous Milky Way falls toward the horizon in this deep skyscape, starting at the top of the frame from the stars of the Southern Cross and the dark Coalsack Nebula. Captured in the dark predawn of February 2nd from Central Victoria, Australia, planet Earth, the 26 day old waning crescent Moon still shines brightly near the horizon. The second and third brightest celestial beacons are Venus and Jupiter along the lower part of the Milky Way's central bulge. Almost in line with the brighter planets and Moon, Saturn is the pinprick of light just visible below and right of the lunar glow. Australia's first astronomers saw the elongated, bulging shape of the familiar Milky Way as a great celestial Emu. The Moon and planets could almost be the Emu's eggs on this starry night.
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