Nature photographers and other fans of planet Earth always look forward to the blue hour. That’s the transition in twilight, just before sunrise or after sunset, when the Sun is below the horizon but land and sky are still suffused with a beautiful blue light. After sunset on August 21, this blue hour snapshot captured the nearly full Moon as it rose opposite the Sun, above the rugged Italian Alps from Cortina d’Ampezzo, Italy. Sharing bluish hues with the sky, the rocky pyramid of Monte Antelao, also known as the King of the Dolomites, is the region’s prominent alpine peak. The moonlight is yellow, but even so this full Moon was known to some as a seasonal Blue Moon. That’s because by one definition the third full Moon of a season with four full moons in it is called a Blue Moon. Recognizing a season as the time between a solstice and an equinox, this season’s fourth full Moon will be rising in the blue hour of September 20, just before September’s equinox. via NASA https://ift.tt/2WqrfdQ

Does a ball drop faster on Earth, Jupiter, or Uranus? The featured animation shows a ball dropping from one kilometer high toward the surfaces of famous solar system bodies, assuming no air resistance. The force of gravity depends on the mass of the attracting object, with higher masses pulling down with greater forces. But gravitational force also depends on distance from the center of gravity, with shorter distances causing the ball to drop faster. Combining both mass and distance, it might be surprising to see that Uranus pulls the ball down slightly slower than Earth, despite containing over 14 times more mass. This happens because Uranus has a much lower density, which puts its cloud tops further away from its center of mass. Although the falling ball always speeds up, if you were on the ball you would not feel this acceleration because you would be in free-fall. Of the three planets mentioned, the video demonstrates a ball drops even faster on Jupiter than either Earth and Uranus. via NASA https://ift.tt/2XLA42C

It’s not the big disk that’s attracting the most attention. Although the big planet-forming disk around the star PDS 70 is clearly imaged and itself quite interesting. It’s also not the planet on the right, just inside the big disk, that’s being talked about the most. Although the planet PDS 70c is a newly formed and, interestingly, similar in size and mass to Jupiter. It’s the fuzzy patch around the planet PDS 70c that’s causing the commotion. That fuzzy patch is thought to be itself a dusty disk that is now forming into moons — and that has never been seen before. The featured image was taken by the Atacama Large Millimeter Array (ALMA) of 66 radio telescopes in the high Atacama Desert of northern Chile. Based on ALMA data, astronomers infer that the moon-forming exoplanetary disk has a radius similar to our Earth’s orbit, and may one day form three or so Luna-sized moons — not very different from our Jupiter’s four. via NASA https://ift.tt/3yiEY40

Is that one galaxy or three? Toward the right of the featured Hubble image of the massive galaxy cluster Abell 3827 is what appears to be a most unusual galaxy — curved and with three centers. A detailed analysis, however, finds that these are three images of the same background galaxy — and that there are at least four more images. Light we see from the single background blue galaxy takes multiple paths through the complex gravity of the cluster, just like a single distant light can take multiple paths through the stem of a wine glass. Studying how clusters like Abell 3827 and their component galaxies deflect distant light gives information about how mass and dark matter are distributed. Abell 3827 is so distant, having a redshift of 0.1, that the light we see from it left about 1.3 billion years ago — before dinosaurs roamed the Earth. Therefore, the cluster’s central galaxies have now surely all coalesced — in a feast of galactic cannibalism — into one huge galaxy near the cluster’s center. via NASA https://ift.tt/3mpzq5m

Spectacular explosions keep occurring in the binary star system named RS Ophiuchi. Every 20 years or so, the red giant star dumps enough hydrogen gas onto its companion white dwarf star to set off a brilliant thermonuclear explosion on the white dwarf’s surface. At about 5,000 light years distant, the resulting nova explosions cause the RS Oph system to brighten up by a huge factor and become visible to the unaided eye. The red giant star is depicted on the right of the above drawing, while the white dwarf is at the center of the bright accretion disk on the left. As the stars orbit each other, a stream of gas moves from the giant star to the white dwarf. Astronomers speculate that at some time in the next 100,000 years, enough matter will have accumulated on the white dwarf to push it over the Chandrasekhar Limit, causing a much more powerful and final explosion known as a supernova. Starting early this month, RS Oph was again seen exploding in a bright nova. via NASA https://ift.tt/3zdbeGQ

These three panels feature the Solar System’s ruling gas giant Jupiter on August 15 as seen from Cebu City, Phillipines, planet Earth. On that date the well-timed telescopic views detail some remarkable performances, transits and mutual events, by Jupiter’s Galilean moons. In the top panel, Io is just disappearing into Jupiter’s shadow at the far right, but the three other large Jovian moons appear against the planet’s banded disk. Brighter Europa and darker Ganymede are at the far left, also casting their two shadows on the gas giant’s cloud tops. Callisto is below and right near the planet’s edge, the three moons in a triple transit across the face of Jupiter. Moving to the middle panel, shadows of Europa and Ganymede are still visible near center but Ganymede has occulted or passed in front of Europa. The bottom panel captures a rare view of Jovian moons in eclipse while transiting Jupiter, Ganymede’s shadow falling on Europa itself. From planet Earth’s perspective, similar mutual events, when Galilean moons occult and eclipse each other, can be seen every six years or so when Jupiter is near its own equinox. via NASA https://ift.tt/2W4Z191

Frames from a camera that spent three moonless nights under the stars create this composite night skyscape. They were recorded during August 11-13 while planet Earth was sweeping through the dusty trail of comet Swift-Tuttle. One long exposure, untracked for the foreground, and the many star tracking captures of Perseid shower meteors were taken from the village of Magyaregres, Hungary. Each aligned against the background stars, the meteor trails all point back to the annual shower’s radiant in the constellation Perseus heroically standing above this rural horizon. Of course the comet dust particles are traveling along trajectories parallel to each other. The radiant effect is due only to perspective, as the parallel tracks appear to converge in the distance against the starry sky. via NASA https://ift.tt/3j1bGlS

Plowing through Earth’s atmosphere at 60 kilometers per second, this bright perseid meteor streaks along a starry Milky Way. Captured in dark Portugal skies on August 12, it moves right to left through the frame. Its colorful trail starts near Deneb (alpha Cygni) and ends near Altair (alpha Aquilae), stars of the northern summer triangle. In fact this perseid meteor very briefly outshines both, two of the brightest stars in planet Earth’s night. The trail’s initial greenish glow is typical of the bright perseid shower meteors. The grains of cosmic sand, swept up dust from periodic comet Swift-Tuttle, are moving fast enough to excite the characteristic green emission of atomic oxygen at altitudes of 100 kilometers or so before vaporizing in an incandescent flash. via NASA https://ift.tt/3xXVXbt

The Ring Nebula (M57), is more complicated than it appears through a small telescope. The easily visible central ring is about one light-year across, but this remarkably deep exposure – a collaborative effort combining data from three different large telescopes – explores the looping filaments of glowing gas extending much farther from the nebula’s central star. This composite image includes red light emitted by hydrogen as well as visible and infrared light. The Ring Nebula is an elongated planetary nebula, a type of nebula created when a Sun-like star evolves to throw off its outer atmosphere to become a white dwarf star. The Ring Nebula is about 2,500 light-years away toward the musical constellation Lyra. via NASA https://ift.tt/3CYt9U7

Except for the rings of Saturn, the Ring Nebula (M57) is probably the most famous celestial circle. Its classic appearance is understood to be due to our own perspective, though. The recent mapping of the expanding nebula’s 3-D structure, based in part on this clear Hubble image,indicates that the nebula is a relatively dense, donut-like ring wrapped around the middle of a (American) football-shaped cloud of glowing gas. The view from planet Earth looks down the long axis of the football, face-on to the ring. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from the dying, once sun-like star, now a tiny pinprick of light seen at the nebula’s center. Intense ultraviolet light from the hot central star ionizes atoms in the gas. The Ring Nebula is about one light-year across and 2,500 light-years away. via NASA https://ift.tt/3z7rMAd