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Astronomy Picture of the Day

A Perseid Fireball and the Milky Way
Image Credit & Copyright: Dandan Huang

Explanation: It was bright and green and flashed as it moved quickly along the Milky Way. It left a trail that took 30 minutes to dissipate. Given the day, August 12, and the direction, away from Perseus, it was likely a small bit from the nucleus of Comet Swift-Tuttle plowing through the Earth’s atmosphere — and therefore part of the annual Perseids meteor shower. The astrophotographer captured the fireball as it shot across the sky in 2018 above a valley in Yichang, Hubei, China. The meteor’s streak, also caught on video, ended near the direction of Mars on the lower left. Next week, the 2021 Perseids meteor shower will peak again. This year the Moon will set shortly after the Sun, leaving a night sky ideal for seeing lots of Perseids from dark and clear locations across planet Earth.

Tomorrow’s picture: Event Horizon Telescope strikes again

Astronomy Picture of the Day

Pluto in Enhanced Color
Image Credit: NASA, Johns Hopkins Univ./APL, Southwest Research Inst.

Explanation: Pluto is more colorful than we can see. Color data and high-resolution images of our Solar System’s most famous dwarf planet, taken by the robotic New Horizons spacecraft during its flyby in 2015 July, have been digitally combined to give an enhanced-color view of this ancient world sporting an unexpectedly young surface. The featured enhanced color image is not only esthetically pretty but scientifically useful, making surface regions of differing chemical composition visually distinct. For example, the light-colored heart-shaped Tombaugh Regio on the lower right is clearly shown here to be divisible into two regions that are geologically different, with the leftmost lobe Sputnik Planitia also appearing unusually smooth. After Pluto, New Horizons continued on, shooting past asteroid Arrokoth in 2019 and has enough speed to escape our Solar System completely.

Tomorrow’s picture: deep galaxy sounds

Astronomy Picture of the Day

Remembering NEOWISE
Image Credit & Copyright: Petr Horalek / Institute of Physics in Opava

Explanation: It was just last July. If you could see the stars of the Big Dipper, you could find Comet NEOWISE in your evening sky. After sunset denizens of the north could look for the naked-eye comet below the bowl of that famous celestial kitchen utensil and above the northwestern horizon. The comet looked like a fuzzy ‘star’ with a tail, though probably not so long a tail as in this memorable skyview recorded from the Czech Republic on July 23th, 2020, near the comet’s closest approach to planet Earth. Photographs of C/2020 F3 (NEOWISE) often did show the comet’s broad dust tail and fainter but separate bluish ion tail extending farther than the eye could follow. Skygazers around the world were delighted to witness Comet NEOWISE, surprise visitor from the outer Solar System.

Tomorrow’s picture: better than Pluto

Astronomy Picture of the Day

Mimas in Saturnlight
Image Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: Peering from the shadows, the Saturn-facing hemisphere of Mimas lies in near darkness alongside a dramatic sunlit crescent. The mosaic was captured near the Cassini spacecraft’s final close approach on January 30, 2017. Cassini’s camera was pointed in a nearly sunward direction only 45,000 kilometers from Mimas. The result is one of the highest resolution views of the icy, crater-pocked, 400 kilometer diameter moon. An enhanced version better reveals the Saturn-facing hemisphere of the synchronously rotating moon lit by sunlight reflected from Saturn itself. To see it, slide your cursor over the image (or follow this link). Other Cassini images of Mimas include the small moon’s large and ominous Herschel Crater.

Tomorrow’s picture: remember when

Astronomy Picture of the Day

The Tulip and Cygnus X-1
Image Credit & Copyright: Carlos Uriarte

Explanation: This tall telescopic field of view looks out along the plane of our Milky Way Galaxy toward the nebula rich constellation Cygnus the Swan. Popularly called the Tulip Nebula, the brightest glowing cloud of interstellar gas and dust above center is also found in the 1959 catalog by astronomer Stewart Sharpless as Sh2-101. Nearly 70 light-years across the complex and beautiful Tulip Nebula blossoms about 8,000 light-years away, shown in a Hubble palette image that maps the glow of the nebula’s sulfur, hydrogen, and oxygen ions into red, green, and blue colors. Ultraviolet radiation from young energetic stars at the edge of the Cygnus OB3 association, including O star HDE 227018, ionizes the atoms and powers the emission from the Tulip Nebula. Also in the field of view is microquasar Cygnus X-1, one of the strongest X-ray sources in planet Earth’s sky. Driven by powerful jets from a black hole accretion disk, its fainter bluish curved shock front is only just visible though, directly above the cosmic Tulip’s petals near the top of the frame.

Tomorrow’s picture: Saturnshine

Astronomy Picture of the Day

Ring Galaxy AM 0644-741
Image Credit: NASA, ESA, Hubble, HLA; Processing: Jonathan Lodge

Explanation: The rim of the large blue galaxy at the right is an immense ring-like structure 150,000 light years in diameter composed of newly formed, extremely bright, massive stars. AM 0644-741 is known as a ring galaxy and was caused by an immense galaxy collision. When galaxies collide, they pass through each other and their individual stars rarely come into contact. The large galaxy’s ring-like shape is the result of the gravitational disruption caused by a small intruder galaxy passing through it. When this happens, interstellar gas and dust become compressed, causing a wave of star formation to move out from the impact point like a ripple across the surface of a pond. Other galaxies in the field of view are background galaxies, not interacting with AM 0644-741. Foreground spiky stars are within our own Milky Way. But the smaller intruder galaxy is caught above and right, near the top of the frame taken by the Hubble Space Telescope. Ring galaxy AM 0644-741 lies about 300 million light years away toward the southern constellation Volans.

Tomorrow’s picture: the flower and the black hole

Astronomy Picture of the Day

Fleming’s Triangular Wisp
Image Credit & Copyright: Anthony Saab

Explanation: Chaotic in appearance, these tangled filaments of shocked, glowing gas are spread across planet Earth’s sky toward the constellation of Cygnus as part of the Veil Nebula. The Veil Nebula itself is a large supernova remnant, an expanding cloud born of the death explosion of a massive star. Light from the original supernova explosion likely reached Earth over 5,000 years ago. The glowing filaments are really more like long ripples in a sheet seen almost edge on, remarkably well separated into the glow of ionized hydrogen atoms shown in blue and oxygen in red hues. Also known as the Cygnus Loop and cataloged as NGC 6979, the Veil Nebula now spans about 6 times the diameter of the full Moon. The length of the wisp corresponds to about 30 light years, given its estimated distance of 2,400 light years. Often identified as Pickering’s Triangle for a director of Harvard College Observatory, it is also named for its discoverer, astronomer Williamina Fleming, as Fleming’s Triangular Wisp.

Tomorrow’s picture: ring of fire galaxy

 


Astronomy Picture of the Day

CG4: A Ruptured Cometary Globule
Image Credit & Copyright: Nicolas Rolland & Martin Pugh

Explanation: Can a gas cloud grab a galaxy? It’s not even close. The “claw” of this odd looking “creature” in the featured photo is a gas cloud known as a cometary globule. This globule, however, has ruptured. Cometary globules are typically characterized by dusty heads and elongated tails. These features cause cometary globules to have visual similarities to comets, but in reality they are very much different. Globules are frequently the birthplaces of stars, and many show very young stars in their heads. The reason for the rupture in the head of this object is not yet known. The galaxy to the left of the globule is huge, very far in the distance, and only placed near CG4 by chance superposition.

Tomorrow’s picture: wisp of star death

Astronomy Picture of the Day

Crescent Neptune and Triton
Image Credit: NASA, Voyager 2

Explanation: Gliding silently through the outer Solar System, the Voyager 2 spacecraft camera captured Neptune and Triton together in crescent phase. The elegant picture of the gas giant planet and its cloudy moon was taken from behind just after closest approach in 1989. It could not have been taken from Earth because Neptune never shows a crescent phase to sunward Earth. The unusual vantage point also robs Neptune of its familiar blue hue, as sunlight seen from here is scattered forward, and so is reddened like the setting Sun. Neptune is smaller but more massive than Uranus, has several dark rings, and emits more light than it receives from the Sun.

Tomorrow’s picture: galaxy grabber

Astronomy Picture of the Day

The Edge of Space
Image Credit & Copyright: Ralf Rohner

Explanation: Where does space begin? For purposes of spaceflight some would say at the Karman line, currently defined as an altitude of 100 kilometers (60 miles). Others might place a line 80 kilometers (50 miles) above Earth’s mean sea level. But there is no sharp physical boundary that marks the end of atmosphere and the beginning of space. In fact, the Karman line itself is near the transition between the upper mesophere and lower thermosphere. Night shining or noctilucent clouds are high-latitude summer apparitions formed at altitudes near the top of the mesophere, up to 80 kilometers or so, also known as polar mesopheric clouds. Auroral bands of the northern (and southern) lights caused by energetic particles exciting atoms in the thermosphere can extend above 80 kilometers to over 600 kilometers altitude. Taken from a cockpit while flying at an altitude of 10 kilometers (33,000 feet) in the realm of stratospheric aeronautics, this snapshot captures both noctilucent clouds and aurora borealis under a starry sky, looking toward planet Earth’s horizon and the edge of space.

Tomorrow’s picture: crescent father and son