NASA Astronomy Picture of the Day:

Taken over the course of an hour shortly after local midnight on December 13, 35 exposures were used to create this postcard from Earth. The composited night scene spans dark skies above the snowy Italian Dolomites during our fair planet's annual Geminid meteor shower. Sirius, alpha star of Canis Major and the brightest star in the night, is grazed by a meteor streak on the right. The Praesepe star cluster, also known as M44 or the Beehive cluster, itself contains about a thousand stars but appears as a smudge of light far above the southern alpine peaks near the top. The shower's radiant is off the top of the frame though, near Castor and Pollux the twin stars of Gemini. The radiant effect is due to perspective as the parallel meteor tracks appear to converge in the distance. As Earth sweeps through the dust trail of asteroid 3200 Phaethon, the dust that creates Gemini's meteors enters Earth's atmosphere traveling at about 22 kilometers per second. Submitted to APOD: Notable images of the 2020 Geminids Meteor Shower

Photo by Stefano Pellegrini

NASA Astronomy Picture of the Day:

What's the matter with the Bullet Cluster? This massive cluster of galaxies (1E 0657-558) creates gravitational lens distortions of background galaxies in a way that has been interpreted as strong evidence for the leading theory: that dark matter exists within. Different analyses, though, indicate that a less popular alternative -- modifying gravity-- could explain cluster dynamics without dark matter, and provide a more likely progenitor scenario as well. Currently, the two scientific hypotheses are competing to explain the observations: it's invisible matter versus amended gravity. The duel is dramatic as a clear Bullet-proof example of dark matter would shatter the simplicity of modified gravity theories. The featured sonified image is a Hubble/Chandra/Magellan composite with red depicting the X-rays emitted by hot gas, and blue depicting the suggested separated dark matter distribution. The sonification assigns low tones to dark matter, mid-range frequencies to visible light, and high tones to X-rays. The battle over the matter in the Bullet cluster is likely to continue as more observations, computer simulations, and analyses are completed. Submitted to APOD: Notable images of the 2020 Geminids Meteor Shower

NASA Astronomy Picture of the Day:

It's happening. Saturn and Jupiter are moving closer and will soon appear in almost exactly the same direction. Coincidentally, on the night of the December solstice -- the longest night of the year in the north and the longest day in the south -- the long-awaited Great Conjunction will occur. Then, about six days from now, Saturn and Jupiter will be right next to each other -- as they are every 20 years. But this juxtaposition is not just any Great Conjunction -- it will be the closest since 1623 because the two planetary giants will pass only 1/10th of a degree from each other -- well less than the apparent diameter of a full moon. In the next few days a crescent moon will also pass a few degrees away from the converging planets and give a preliminary opportunity for iconic photos. The featured illustration shows the approach of Saturn and Jupiter during November and December over the French Alps. Growing Gallery: Notable images of the Great Conjunction submitted to APOD

Photo by Sebastian Voltmer

NASA Astronomy Picture of the Day:

The streak across the sky is a capsule returning from an asteroid. It returned earlier this month from the near-Earth asteroid 162173 Ryugu carrying small rocks and dust from its surface. The canister was released by its mothership, Japan's Hayabusa2, a mission that visited Ryugu in 2018, harvested a surface sample in 2019, and zoomed back past Earth. The jettisoned return capsule deployed a parachute and landed in rural Australia. A similar mission, NASA's OSIRIS- REx, recently captured rocks and dust from a similar asteroid, Bennu, and is scheduled to return its surface sample to Earth in 2023. Analyses of compounds from these asteroids holds promise to give humanity new insights about the early Solar System and new clues about how water and organic matter came to be on Earth. Experts Debate: How will humanity first discover extraterrestrial life?

NASA Astronomy Picture of the Day:

Where do Geminid meteors come from? In terms of location on the sky, as the featured image composite beautifully demonstrates, the sand-sized bits of rock that create the streaks of the Geminids meteor shower appear to flow out from the constellation of Gemini. In terms of parent body, Solar System trajectories point to the asteroid 3200 Phaethon -- but this results in a bit of a mystery since that unusual object appears mostly dormant. Perhaps, 3200 Phaethon undergoes greater dust-liberating events than we know. Over 50 meteors including a bright fireball were captured during the peak of the 2015 Geminids Meteor Shower streaking above Xinglong Observatory in China. The Geminids of December are one of the most predictable and active meteor showers. This year's Geminids peak tonight and should be particularly good because, in part, the nearly new Moon will only rise toward dawn and so not brighten the sky.

Photo by Steed YuNightChina.net

NASA Astronomy Picture of the Day:

During this northern summer Saturn and Jupiter were both near opposition, opposite the Sun in planet Earth's sky. Their paired retrograde motion, seen about every 20 years, is followed from 19 June through 28 August in this panoramic composite as they wander together between the stars in western Capricornus and eastern Sagittarius. But this December's skies find them drawing even closer together. Jupiter and Saturn are now close, bright celestial beacons in the west after sunset. On solstice day December 21 they will reach their magnificent 20 year Great Conjunction. Then the two largest worlds in the Solar System will appear in Earth's sky separated by only about 1/5 the apparent diameter of a Full Moon.

Photo by Tunc Tezel

NASA Astronomy Picture of the Day:

Many bright nebulae and star clusters in planet Earth's sky are associated with the name of astronomer Charles Messier from his famous 18th century catalog. His name is also given to these two large and remarkable craters on the Moon. Standouts in the dark, smooth lunar Sea of Fertility or Mare Fecunditatis, Messier (left) and Messier A have dimensions of 15 by 8 and 16 by 11 kilometers respectively. Their elongated shapes are explained by the extremely shallow-angle trajectory followed by an impactor, moving left to right, that gouged out the craters. The shallow impact also resulted in two bright rays of material extending along the surface to the right, beyond the picture. Intended to be viewed with red/blue glasses (red for the left eye), this striking stereo picture of the crater pair was recently created from high resolution scans of two images (AS11-42-6304, AS11-42-6305) taken during the Apollo 11 mission to the Moon.

NASA Astronomy Picture of the Day:

It's easy to get lost following the intricate looping filaments in this detailed image of supernova remnant Simeis 147. Also cataloged as Sharpless 2-240 it goes by the popular nickname, the Spaghetti Nebula. Seen toward the boundary of the constellations Taurus and Auriga, it covers nearly 3 degrees or 6 full moons on the sky. That's about 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. This composite includes image data taken through narrow-band filters where reddish emission from ionized hydrogen atoms and doubly ionized oxygen atoms in faint blue-green hues trace the shocked, glowing gas. The supernova remnant has an estimated age of about 40,000 years, meaning light from the massive stellar explosion first reached Earth 40,000 years ago. But the expanding remnant is not the only aftermath. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the original star's core.

Photo by Georges Attard

NASA Astronomy Picture of the Day:

This was one great scientific instrument. Starting in 1963, the 305-meters across Arecibo Telescope in Puerto Rico USA reigned as the largest single-dish radio telescope in the world for over 50 years. Among numerous firsts and milestones, data from Arecibo has been used to measure the spin of Mercury, map the surface of Venus, discover the first planets outside of our Solar System, verify the existence of gravitational radiation, search for extraterrestrial intelligence, and, reportedly, locate hidden military radar by tracking their reflections from the Moon. In the process of being decommissioned, the Arecibo Telescope suffered a catastrophic structural collapse early this month, as seen in the featured composite video.

NASA Astronomy Picture of the Day:

Don’t miss the coming great conjunction. In just under two weeks, the two largest planets in our Solar System will angularly pass so close together in Earth's sky that the Moon would easily be able to cover them both simultaneously. This pending planetary passage -- on December 21 -- will be the closest since 1623. Jupiter and Saturn will remain noticeably bright and can already be seen together toward the southwest just after sunset. Soon after dusk is the best time to see them -- because they set below the horizon soon after. In mid-November, the Jovian giants were imaged together here about three degrees apart -- and slowly closing. The featured image, including a crescent moon, captured the dynamic duo beyond the Cape Murro di Porco Lighthouse in Syracuse, Sicily, Italy.

Photo by Kevin Saragozza

NASA Astronomy Picture of the Day:

What's that below those strange clouds? Presidents. If you look closely, you may recognize the heads of four former US Presidents carved into famous Mount Rushmore in South Dakota, USA. More obvious in the featured image are the unusual mammatus clouds that passed briefly overhead. Both were captured together by a surprised tourist with a quick camera in early September. Unlike normal flat-bottomed clouds which form when moist and calm air plateaus rise and cool, bumpy mammatus clouds form as icy and turbulent air pockets sink and heat up. Such turbulent air is frequently accompanied by a thunderstorm. Each mammatus lobe spans about one kilometer. The greater mountain is known to native Lakota Sioux as Six Grandfathers, deities responsible for the directions north, south, east, west, up, and down.

Photo by Laure Mattuzzi

NASA Astronomy Picture of the Day:

These dark pillars may look destructive, but they are creating stars. This pillar-capturing image of the inside of the Eagle Nebula, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust. The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars. At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away. The pillars of creation have been imaged more recently in infrared light by Hubble, NASA's Spitzer Space Telescope, and ESA's Herschel Space Observatory -- showing new detail. Be Honest: Have you seen this image before?