3I ATLAS Flyby

Attention grabbing interstellar visitor 3I/ATLAS made its not-so-close flyby of our fair planet on December 19 at a distance of 1.8 astronomical units. That's about 900 light-seconds. Still, this deep exposure captures the comet from another star system as it gently swept across a faint background of stars in the constellation Leo about 4 days earlier, on the night of December 15. Though faint, colors emphasized in the image data, show off the comet's yellowish dust tail and bluish ion tail along with a greenish tinged coma. And even while scrutinized by arrays of telescopes and spacecraft from planet Earth, 3I ATLAS is headed out of the Solar System. It's presently moving outward along a hyperbolic trajectory at about 64 kilometers per second relative to the Sun, too fast to be bound the Sun's gravity. via NASA https://ift.tt/gAyCKop

Unicorn, Fox Fur and Christmas Tree

A star forming region cataloged as NGC 2264, this beautiful but complex arrangement of interstellar gas and dust is about 2,700 light-years distant in the faint but fanciful constellation Monoceros, the Unicorn. Seen toward the celestial equator and near the plane of our Milky Way galaxy, the seasonal skyscape mixes reddish emission nebulae excited by energetic light from newborn stars with dark interstellar dust clouds. Where the otherwise obscuring dust clouds lie close to the hot, young stars, they also reflect starlight, forming blue reflection nebulae. In fact, bright variable star S Monocerotis is immersed in a blue-tinted haze near center. Arrayed with a simple triangular outline above S Monocerotis, the stars of NGC 2264 are popularly known as the Christmas Tree star cluster. Carved by energetic starlight, the Cone Nebula sits upside down at the apex of this cosmic Christmas tree while the dusty, convoluted pelt of glowing gas and dust under the tree is called the Fox Fur Nebula. This rich telescopic frame spans about 1.5 degrees or 3 full moons on the sky top to bottom, covering nearly 80 light-years at the distance of NGC 2264. via NASA https://ift.tt/oD4mBwv

What are these little red dots (LRDs)? Nobody knows. Discovered only last year, hundreds of LRDs have now been found by the James Webb Space Telescope in the early universe. Although extremely faint, LRDs are now frequently identified in deep observations made for other purposes. A wide-ranging debate is raging about what LRDs may be and what importance they may have. Possible origin hypotheses include accreting supermassive black holes inside clouds of gas and dust, bursts of star formation in young dust-reddened galaxies, and dark matter powered gas clouds. The highlighted images show six nearly featureless LRDs listed under the JWST program that found them, and z, a distance indicator called cosmological redshift. Additionally, searches are underway in our nearby universe to try to find whatever previous LRDs might have become today. via NASA https://ift.tt/0cJ7CIr

What's happening in the sky? Lightning. The most commonly seen type of lightning involves flashes of bright white light between clouds. Over the past 50 years, though, other types of upper-atmospheric lightning have been confirmed, including tentacled red sprites and ringed ELVES. Although both last only a small fraction of a second, sprites are brighter and easier to photograph than their more common electrical-discharge cousins. ELVES are rapidly expanding rings that are thought to be created when an electromagnetic pulse shoots upward from charged clouds and impacts the ionosphere, causing nitrogen molecules to glow. Capturing either form of lightning takes patience and experience -- capturing them both together, since they usually occur separately, is rare. The featured image is a frame from a video recorded from Possagno, Italy late last month above a distant thunderstorm over the Adriatic Sea. via NASA https://ift.tt/H8G3lMD

Yesterday the Sun reached its southernmost point in planet Earth's sky. Called a solstice, many cultures mark yesterday's date as a change of seasons -- from autumn to winter in Earth's Northern Hemisphere and from spring to summer in Earth's Southern Hemisphere. The featured image was taken just before the longest night of the 2025 northern year at Stonehenge in United Kingdom. There, through stones precisely placed 4,500 years ago, a 4.5 billion year old large glowing orb is seen setting. Even given the precession of the Earth's rotational axis over the millennia, the Sun continues to set over Stonehenge in an astronomically significant way. via NASA https://ift.tt/UJDqr6Y

A Solstice Sun Tattoo

The word solstice is from the Latin for Sun and to pause or stand still. And in the days surrounding a solstice the Sun's annual north-south drift in planet Earth's sky does slow down, pause, and then reverse direction. So near the solstice the daily path of the Sun through the sky really doesn't change much. In fact, near the December solstice, the Sun's consistent, low arc through northern hemisphere skies, along with low surface temperatures, has left a noticeable imprint on this path to the mountain town of Peaio in northern Italy. The morning frost on the road has melted away only where the sunlight was able to reach the ground. But it remains in the areas persistently shadowed by the fence, tattooing in frost an image of the fence on the asphalt surface. via NASA https://ift.tt/njPNG2s

Long Shadows of the Montes Caucasus

When the Moon is at its first quarter phase, the Sun rises along the Montes Caucasus as seen from the lunar surface. The lunar mountain range casts the magnificent, spire-like shadows in this telescopic view from planet Earth, looking along the lunar terminator or the boundary between lunar night and day. Named for Earth's own Caucasus Mountains, the rugged lunar Montes Caucasus peaks, up to 6 kilometers high, are located between the smooth Mare Imbrium to the west and Mare Serenitatis to the east. Still mostly in shadow in this first quarter lunarscape, at the left (west) impact craters reflect the light of the rising Sun along their outer, eastern crater walls. via NASA https://ift.tt/3fUmtag