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Explanation: While hunting for comets in the skies above 18th century France, astronomer Charles Messier diligently kept a list of the things he encountered that were definitely not comets. This is number 27 on his now famous not-a-comet list. In fact, 21st century astronomers would identify it as a planetary nebula, but it's not a planet either, even though it may appear round and planet-like in a small telescope. Messier 27 (M27) is an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core. The nebula forms as the star's...

Explanation: In cosmic brush strokes of glowing hydrogen gas, this beautiful skyscape unfolds across the plane of our Milky Way Galaxy and the center of the northern constellation Cygnus the Swan. The featured image spans about six degrees. Bright supergiant star Gamma Cygni (Sadr) to the upper left of the image center lies in the foreground of the complex gas and dust clouds and crowded star fields. Left of Gamma Cygni, shaped like two luminous wings divided by a long dark dust lane is IC 1318, whose popular name is understandably the Butterfly Nebula. The more compact, bright nebula at...

One of the surest signs that late summer is here in the northern hemisphere is the arrival of the Milky Way in the early evening sky....the star-dappled plane of our home galaxy sits almost due south and stretches far to the north. This is also why we refer to the triangular shaped asterism formed by the bright stars of Altair, Deneb and Vega as the Summer Triangle. Two of these stars are the focus of a fascinating mythos from the Far East, and a poetic celestial configuration that commemorates star-crossed lovers lost. We first heard of tales of Tanabata while...

Explanation: Will Comet Catalina become visible to the unaided eye? Given the unpredictability of comets, no one can say for sure, but it seems like a good bet. The comet was discovered in 2013 by observations of the Catalina Sky Survey. Since then, Comet C/2013 US10 (Catalina) has steadily brightened and is currently brighter than 8th magnitude, making it visible with binoculars and long-duration camera images. As the comet further approaches the inner Solar System it will surely continue to intensify, possibly becoming a naked eye object sometime in October and peaking sometime in late November. The comet will reside...

Explanation: Have you ever seen the Andromeda galaxy? Although M31 appears as a faint and fuzzy blob to the unaided eye, the light you see will be over two million years old, making it likely the oldest light you ever will see directly. Now rising near a few hours after sunset from mid-latitude northern locations, Andromeda is rising earlier each night and will be visible to northerners all night long starting in September. The featured image captured Andromeda rising above the Italian Alps last month. As cool as it may be to see this neighboring galaxy to our Milky Way...

Explanation: This is the mess that is left when a star explodes. The Crab Nebula, the result of a supernova seen in mysterious filaments. The filaments are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion. The featured image, taken by the Hubble Space Telescope, is presented in three colors chosen for scientific interest. The Crab Nebula spans about 10 light-years. In the nebula's very center lies a pulsar: a neutron star as massive as the Sun but with only the size of...

Explanation: This dramatic outburst from the nucleus of Comet 67P/Churyumov-Gerasimenko occured on August 12, just hours before perihelion, its closest approach to the Sun. Completing an orbit of the Sun once every 6.45 years, perihelion distance for this periodic comet is about 1.3 astronomical units (AU), still outside the orbit of planet Earth (at 1 AU). The stark image of the 4 kilometer wide, double-lobed nucleus in bright sunlight and dark shadows was taken by the Rosetta spacecraft's science camera about 325 kilometers away. Too close to see the comet's growing tail, Rosetta maintains its ringside seat to watch the...

Explanation: Dusty debris from periodic Comet Swift-Tuttle was swept up by planet Earth this week. Vaporized by their passage through the dense atmosphere at 59 kilometers per second, the tiny grains produced a stream of Perseid meteors. A bright, colorful Perseid meteor flash was captured during this 20 second exposure. It made its ephemeral appearance after midnight on August 12, in the moonless skies over the broad granite dome of Enchanted Rock State Natural Area, central Texas, USA. Below the Perseid meteor, trees stand in silhouette against scattered lights along the horizon and the faint Milky Way, itself cut by...

Explanation: Have you watched the Perseid meteor shower? Though the annual shower's predicted peak was last night, meteor activity should continue tonight (August 13/14), best enjoyed by just looking up in clear, dark skies after midnight. Of course, this year's Perseid shower has the advantage of being active near the August 14 New Moon. Since the nearly New Moon doesn't rise before the morning twilight many fainter meteors are easier to spot until then, with no interference from bright moonlight. The Perseid meteor shower last occurred near a New Moon in 2013. That's when the exposures used to construct this...

Explanation: Tonight the Perseid Meteor Shower reaches its maximum. Grains of icy rock will streak across the sky as they evaporate during entry into Earth's atmosphere. These grains were shed from Comet Swift-Tuttle. The Perseids result from the annual crossing of the Earth through Comet Swift-Tuttle's orbit, and are typically the most active meteor shower of the year. Although it is hard to predict the level of activity in any meteor shower, in a clear dark sky an observer might see a meteor a minute. This year's Perseids occur just before a new Moon and so the relatively dark sky...

The Los Angeles Times (8/10, Khan) reports that an international study led by Simon Driver of the University of Western Australia and presented at the International Astronomical Union meeting on Monday found that the amount of light the 200,000 galaxies are outputting is half of what they did two billion years ago, meaning “the universe is dying.” The article notes that seven telescopes were used in the study, including NASA’s Wide-field Infrared Survey Explorer spacecraft. Driver said that the conclusion is consistent with each of the three indicators measured. However, the universe should continue to exist “far into the foreseeable...

Explanation: Have you ever seen a halo around the Moon? Such 22 degree rings around the Moon -- caused by ice crystals falling in the Earth's atmosphere -- are somewhat rare. OK, but have you ever seen a blue moon? Given the modern definition of blue moon -- the second full moon occurring in a calendar month -- these are also rare. What is featured above might therefore be considered doubly rare -- a halo surrounding a blue moon. The featured image was taken late last month near Zhongshan Station in Antarctica. Visible in the foreground are a power generating...

The Oort Cloud is a theoretical spherical cloud of predominantly icy planetesimals that is believed to surround the Sun at a distance of up to around 100,000 AU (2 ly). This places it in interstellar space, beyond the Sun’s Heliosphere where it defines the cosmological boundary between the Solar System and the region of the Sun’s gravitational dominance. Like the Kuiper Belt and the Scattered Disc, the Oort Cloud is a reservoirs of trans-Neptunian objects, though it is over a thousands times more distant from our Sun as these other two. The idea of a cloud of icy infinitesimals was...

Explanation: These three bright nebulae are often featured in telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the large nebula left of center, and colorful M20 on the right. The third, NGC 6559, is above M8, separated from the larger nebula by a dark dust lane. All three are stellar nurseries about five thousand light-years or so distant. The expansive M8, over a hundred light-years across, is also known as the Lagoon Nebula. M20's popular moniker is the Trifid. Glowing...

Explanation: Sometimes galaxies form groups. For example, our own Milky Way Galaxy is part of the Local Group of Galaxies. Small, compact groups, like Hickson Compact Group 87 (HCG 87) shown above, are interesting partly because they slowly self-destruct. Indeed, the galaxies of HCG 87 are gravitationally stretching each other during their 100-million year orbits around a common center. The pulling creates colliding gas that causes bright bursts of star formation and feeds matter into their active galaxy centers. HCG 87 is composed of a large edge-on spiral galaxy visible near the image center, an elliptical galaxy visible to its...

Explanation: By planet Earth's calendar, the Curiosity Mars Rover reached its 3rd anniversary on the surface of the Red Planet on August 6. To celebrate, gaze across this dramatic panoramic view of diverse terrain typical of the rover's journey to the layered slopes of Aeolis Mons, also known as Mount Sharp. Recorded with Curiosity's Mast Camera instrument, the scene looks south across gravel, sand ripples, and boulders toward rounded buttes. In the background, higher layers at left are toward the southeast, with southwest at panorama right. The individual images composing the view were taken on Curiosity's mission sols (martian days)...

Explanation: The Moon was new on July 16. Its familiar nearside facing the surface of planet Earth was in shadow. But on that date a million miles away, the Deep Space Climate Observatory (DSCOVR) spacecraft's Earth Polychromatic Imaging Camera (EPIC) captured this view of an apparently Full Moon crossing in front of a Full Earth. In fact, seen from the spacecraft's position beyond the Moon's orbit and between Earth and Sun, the fully illuminated lunar hemisphere is the less familiar farside. Only known since the dawn of the space age, the farside is mostly devoid of dark lunar maria that...

EGSY8p7 is the most distant confirmed galaxy whose spectrum obtained with the W. M. Keck Observatory places it at a redshift of 8.68 at a time when the Universe was less than 600 million years old. The illustration shows the remarkable progress made in recent years in probing early cosmic history. Such studies are important in understanding how the Universe evolved from an early dark period to one when galaxies began to shine. Hydrogen emission from EGSY8p7 may indicate it is the first known example of an early generation of young galaxies emitting unusually strong radiation. Credit: Adi Zitrin, California...

Explanation: These two detailed, true color images of Pluto were captured during the historic New Horizons flyby last month. With slightly different perspectives on the now recognizeable surface features they are presented in this first high quality stereo pair intended for viewing by denizens of planet Earth. The left hand image (left eye) is a mosaic recorded when the spacecraft was about 450,000 kilometers from Pluto. The right single image was acquired earlier, a last full look before the spacecraft's closest approach. Despite a difference in resolution, the pair combine for a stunning 3D perception of the distant, underworldly terrain....

Explanation: Circinus X-1 is an X-ray binary star known for its erratic variability. In the bizarre Circinus X-1 system, a dense neutron star, the collapsed remnant of a supernova explosion, orbits with a more ordinary stellar companion. Observations of the X-ray binary in months following an intense X-ray flare from the source in 2013 progressively revealed striking concentric rings - bright X-ray light echoes from four intervening clouds of interstellar dust. In this X-ray/optical composite, the swaths of Chandra Observatory X-ray image data showing partial outlines of the rings are in false colors. Remarkably, timing the X-ray echoes, along with...