Free Republic

Explanation: Comet C/2023 A3 (Tsuchinshan–ATLAS) is growing brighter in planet Earth's sky. Fondly known as comet A3, this new visitor to the inner Solar System is traveling from the distant Oort cloud. The comet reached perihelion, its closest approach to the Sun, on September 27 and will reach perigee, its closest to our fair planet, on October 12, by then becoming an evening sky apparition. But comet A3 was an early morning riser on September 30 when this image was made. Its bright coma and already long tail share a pre-dawn skyscape from Praia Grande, Santa Catarina in southern Brazil...

Explanation: The second solar eclipse of 2024 began in the Pacific. On October 2nd the Moon's shadow swept from west to east, with an annular eclipse visible along a narrow antumbral shadow path tracking mostly over ocean, crossing land near the southern tip of South America, and ending in the southern Atlantic. The dramatic total annular eclipse phase is known to some as a ring of fire. Still, a partial eclipse of the Sun was experienced over a wide region. Captured at one of its earliest moments, October's eclipsed Sun is seen just above the clouds near sunrise in this...

Explanation: It is the largest satellite galaxy of our home Milky Way Galaxy. If you live in the south, the Large Magellanic Cloud (LMC) is quite noticeable, spanning about 10 degrees across the night sky, which is 20 times larger than the full moon towards the southern constellation of the dolphinfish (Dorado). Being only about 160,000 light years away, many details of the LMC's structure can be seen, such as its central bar and its single spiral arm. The LMC harbors numerous stellar nurseries where new stars are being born, which appear in pink in the featured image. It is...

Explanation: How far can black hole jets extend? A new record was found just recently with the discovery of a 23-million light-year long jet pair from a black hole active billions of years ago. Dubbed Porphyrion for a mythological Greek giant, the impressive jets were created by a type of black hole that does not usually create long jets -- one that is busy creating radiation from infalling gas. The featured animated video depicts what it might look like to circle around this powerful black hole system. Porphyrion is shown as a fast stream of energetic particles, and the bright...

Explanation: The new comet has passed its closest to the Sun and is now moving closer to the Earth. C/2023 A3 (Tsuchinshan–ATLAS) is currently moving out from inside the orbit of Venus and on track to pass its nearest to the Earth in about two weeks. Comet Tsuchinshan-ATLAS, pronounced "Choo-cheen-shahn At-less,", is near naked-eye visibility and easily picked up by long-exposure cameras. The comet can also now be found by observers in Earth's northern hemisphere as well as the south. The featured image was captured just a few days ago above Zacatecas, Mexico. Because clouds were obscuring much of the...

Explanation: Is this really the famous Pleiades star cluster? Known for its iconic blue stars, the Pleiades is shown here in infrared light where the surrounding dust outshines the stars. Here, three infrared colors have been mapped into visual colors (R=24, G=12, B=4.6 microns). The base images were taken by NASA's orbiting Wide Field Infrared Survey Explorer (WISE) spacecraft. Cataloged as M45 and nicknamed the Seven Sisters, the Pleiades star cluster is by chance situated in a passing dust cloud. The light and winds from the massive Pleiades stars preferentially repel smaller dust particles, causing the dust to become stratified...

Explanation: Shockwaves ripple across the glare as a launch eclipses the setting Sun in this exciting close-up. Captured on September 17, the roaring Falcon 9 rocket carried European Galileo L13 navigation satellites to medium Earth orbit after a lift-off from Cape Canaveral on Florida's space coast. The Falcon 9 booster returned safely to Earth about 8.5 minutes later, notching the 22nd launch and landing for the reusable workhorse launch vehicle. But where did it land? Just Read the Instructions.

Explanation: The twenty galaxies arrayed in these panels are part of an ambitious astronomical survey of tidal stellar streams. Each panel presents a composite view; a deep, inverted image taken from publicly available imaging surveys of a field that surrounds a nearby massive galaxy image. The inverted images reveal faint cosmic structures, star streams hundreds of thousands of light-years across, that result from the gravitational disruption and eventual merger of satellite galaxies in the local universe. Such surveys of mergers and gravitational tidal interactions between massive galaxies and their dwarf satellites are crucial guides for current models of galaxy formation...

Explanation: In 1716, English astronomer Edmond Halley noted, "This is but a little Patch, but it shows itself to the naked Eye, when the Sky is serene and the Moon absent." Of course, M13 is now less modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Sharp telescopic views like this one reveal the spectacular cluster's hundreds of thousands of stars. At a distance of 25,000 light-years, the cluster stars crowd into a region 150 light-years in diameter. Approaching the cluster core, upwards of 100 stars could be contained...

Explanation: Comet Tsuchinshan-ATLAS is now visible in the early morning sky. Diving into the inner Solar System at an odd angle, this large dirty iceberg will pass its closest to the Sun -- between the orbits of Mercury and Venus -- in just two days. Long camera exposures are now capturing C/2023 A3 (Tsuchinshan–ATLAS), sometimes abbreviated as just A3, and its dust tail before and during sunrise. The featured image composite was taken four days ago and captured the comet as it rose above Lake George, NSW, Australia. Vertical bands further left are images of the comet as the rising...

Explanation: This dusty region is forming stars. Part of a sprawling molecular cloud complex that resembles, to some, a rampaging baboon, the region is a relatively close by 500 light-years away toward the constellation Corona Australis. That's about one third the distance of the more famous stellar nursery known as the Orion Nebula. Mixed with bright nebulosities, the brown dust clouds effectively block light from more distant background stars in the Milky Way and obscure from view embedded stars still in the process of formation. The eyes of the dust creature in the featured image are actually blue reflection nebulas...

Explanation: What will happen as this already bright comet approaches? Optimistic predictions have Comet C/2023 A3 (Tsuchinshan–ATLAS) briefly becoming easily visible to the unaided eye -- although the future brightness of comets are notoriously hard to predict, and this comet may even break up in warming sunlight. What is certain is that the comet is now unexpectedly bright and is on track to pass its closest to the Sun (0.39 AU) later this week and closest to the Earth (0.47 AU) early next month. The featured image was taken in late May as Comet Tsuchinshan–ATLAS, discovered only last year, passed...

Explanation: Chicago, in a way, is like a modern Stonehenge. The way is east to west, and the time is today. Today, and every equinox, the Sun will set exactly to the west, everywhere on Earth. Therefore, today in Chicago, the Sun will set directly down the long equatorially-aligned grid of streets and buildings, an event dubbed #chicagohenge. Featured here is a Chicago Henge picture taken during the equinox in mid-September of 2017 looking along part of Upper Wacker Drive. Many cities, though, have streets or other features that are well-aligned to Earth's spin axis. Therefore, quite possibly, your favorite...

Explanation: The defining astronomical moment of this September's equinox is at 12:44 UTC on September 22, when the Sun crosses the celestial equator moving south in its yearly journey through planet Earth's sky. That marks the beginning of fall for our fair planet in the northern hemisphere and spring in the southern hemisphere, when day and night are nearly equal around the globe. Of course, if you celebrate the astronomical change of seasons by watching a sunrise you can also look for crepuscular rays. Outlined by shadows cast by clouds, crepuscular rays can have a dramatic appearance in the twilight...

Explanation: For northern hemisphere dwellers, September's Full Moon was the Harvest Moon. On September 17/18 the sunlit lunar nearside passed into shadow, just grazing Earth's umbra, the planet's dark, central shadow cone, in a partial lunar eclipse. Over the two and half hours before dawn a camera fixed to a tripod was used to record this series of exposures as the eclipsed Harvest Moon set behind Spiš Castle in the hazy morning sky over eastern Slovakia. Famed in festival, story, and song, Harvest Moon is just the traditional name of the full moon nearest the autumnal equinox. According to lore...

Explanation: Spanning light-years, this suggestive shape known as the Seahorse Nebula floats in silhouette against a rich, luminous background of stars. Seen toward the royal northern constellation of Cepheus, the dusty, dark nebula is part of a Milky Way molecular cloud some 1,200 light-years distant. It is also listed as Barnard 150 (B150), one of 182 dark markings of the sky cataloged in the early 20th century by astronomer E. E. Barnard. Packs of low mass stars are forming within, but their collapsing cores are only visible at long infrared wavelengths. Still, the colorful Milky Way stars of Cepheus add...

Explanation: New stars are born from the remnants of dead stars. The gaseous remnant of the gravitational collapse and subsequent death of a very massive star in our Milky Way created the G296.5+10.0 supernova remnant, of which the featured Mermaid Nebula is part. Also known as the Betta Fish Nebula, the Mermaid Nebula makes up part of an unusual subclass of supernova remnants that are two-sided and nearly circular. Originally discovered in X-rays, the filamentary nebula is a frequently studied source also in radio and gamma-ray light. The blue color visible here originates from doubly ionized oxygen (OIII), while the...

Explanation: Cosmic clouds form fantastic shapes in the central regions of emission nebula IC 1805. The clouds are sculpted by stellar winds and radiation from massive hot stars in the nebula's newborn star cluster, Melotte 15. About 1.5 million years young, the cluster stars are scattered in this colorful skyscape, along with dark dust clouds in silhouette against glowing atomic gas. A composite of narrowband and broadband telescopic images, the view spans about 15 light-years and includes emission from ionized hydrogen, sulfur, and oxygen atoms mapped to green, red, and blue hues in the popular Hubble Palette. Wider field images...

Explanation: Why does this large crater on Mercury have two rings and a smooth floor? No one is sure. The unusual feature called Vivaldi Crater spans 215 kilometers and was imaged again in great detail by ESA's and JAXA's robotic BepiColombo spacecraft on a flyby earlier this month. A large circular feature on a rocky planet or moon is usually caused by either an impact by a small asteroid or a comet fragment, or a volcanic eruption. In the case of Vivaldi, it is possible that both occurred -- a heavy strike that caused a smooth internal lava flow. Double-ringed...

Explanation: Have you ever seen the Man in the Moon? This common question plays on the ability of humans to see pareidolia -- imagining familiar icons where they don't actually exist. The textured surface of Earth's full Moon is home to numerous identifications of iconic objects, not only in modern western culture but in world folklore throughout history. Examples, typically dependent on the Moon's perceived orientation, include the Woman in the Moon and the Rabbit in the Moon. One facial outline commonly identified as the Man in the Moon starts by imagining the two dark circular areas -- lunar maria...