Tabla de contenidos para December 2025 en Astronomy

To take on the role of editor-in-chief of Astronomy is a tremendously humbling honor. Like many of you, I grew up looking through an eyepiece and devouring anything written about the cosmos that I could get my hands on, including this magazine. I’m looking forward to working with our talented team to carry on the title’s legacy and bring you the best magazine we can. We also plan to find new ways to serve and grow our community of observers, imagers, and all those fascinated by the universe and our place in it. I am thrilled that Dave Eicher is staying on as editor emeritus. It’s been a privilege to work with and learn from him over the past five years. After the magazine’s founder, Steve Walther, nobody has done…

DUST BUSTER Astronomers imaging the young Sun-like star WISPIT 2 spotted a 5-Jupiter-mass gas giant carving a clear path in the disk of dust and gas around its sun. It’s only the second planet seen at such an early age around a star like our own. TEST SHOT On July 20, NASA’s Psyche imaged Earth and the Moon from a distance of 180 million miles (290 million km). These engineering shots indicate how the cameras respond to reflected sunlight, which is how they will study the asteroid Psyche upon arrival in 2029. NEW MOON In February, JWST discovered a new moon orbiting Uranus, designated S/2025 U1. Just 6 miles (10 km) across, it is smaller and fainter than any of the planet’s other moons — and was impossible for Voyager…

IDENTITY UNKNOWN Earendel, hailed in 2022 as the most distant single star ever discovered (28 billion light-years away), may actually be a tightly packed star cluster, according to new modeling of data taken by JWST. REACTOR RUSH In August, NASA declared its intent to place a nuclear reactor on the Moon by 2030, aiming to preempt similar plans from China and Russia. The agency solicited proposals from industry for a fission power system producing at least 100,000 watts of power. STRIKE THREE The Earth-sized exoplanet TRAPPIST-1 d, which lies on the edge of its star’s habitable zone, does not have a thick atmosphere, JWST transmission spectroscopy has found. That’s the third planet in the system, after b and c, where JWST has not seen evidence of a significant atmosphere. BOUNCING…

THE LAVA-FILLED GRIMALDI BASIN is easily identified on the western limb of the Moon as the last patch of darkness west of the huge Oceanus Procellarum. But when the first rays of sunlight tickle its clumpy rim on the evening of the 3rd, only a “Mickey Mouse head” trio of craters points the way in the lunar southwest. Fully illuminated on the 4th, the highly battered crater rim is direct evidence of its age. Several interesting sights have also appeared next to Grimaldi, notably the equally large and battered Riccioli closer to the terminator. That crater has a much rougher floor because it was a little too far from Procellarum’s lava floods to get filled up like Grimaldi. Use a dark filter on your eyepiece to reduce the stark brightness levels…

IF YOU WERE TO ASK a group of dedicated amateur astronomers to list their favorite telescopic targets, few if any would mention asteroids. That’s easy to understand. The typical asteroid lacks the jaw-dropping visual impact of the Moon or Saturn. Through the eyepiece, an asteroid is an ordinary-looking stellar speck. In fact, the word asteroid comes from the Greek word asteroeides, which means “starlike.” My interest in observing asteroids began in the summer of 1971 when I came across information in an astronomy magazine about the then-visible asteroid 4 Vesta. Using the accompanying finder chart, I spotted Vesta with a handheld 6x refractor. A few months later, another featured asteroid led me to 8 Flora, which I spotted using a 3-inch f/10 reflecting telescope (Edmund Scientific’s classic Space Conqueror). That…

Since 3D printing became accessible to the average consumer in the 2010s, the internet has exploded with printable designs from creators around the world. Sites like Thingiverse and Printables host millions of downloadable files, and decent printers can be had for as little as $200. I got a Prusa i3 Mk3s+ for Christmas in 2022 and have scarcely stopped printing since. One of my most ambitious projects so far? A fully functional 8-inch f/5 Newtonian telescope. This 3D-printed Dobsonian, called the Leavitt after astronomer Henrietta Swan Leavitt, was designed by a Printables user named Novel Tinker. Not every component is printed, of course — I had to buy metal fasteners, springs, glue, truss rods, and the mirrors. But Novel Tinker provided a detailed parts list and assembly instructions, even recommending…

LUNAR PHASES All dates are for the Eastern time zone. A Full Moon rises at sunset and remains visible all night; a New Moon crosses the sky with the Sun and can’t be seen. THE MOON is Earth’s nearest neighbor and the only celestial object humans have visited. Because of its changing position relative to the Sun and Earth, the Moon appears to go through phases, from a slender crescent to Full Moon and back. The best times to observe our satellite through a telescope come a few days on either side of its two Quarter phases. For the best detail, look along the terminator — the line separating the sunlit and dark parts. VENUS remains a fixture in the western evening sky from late February through September. It then disappears…

THE WORLD LOST A TRUE HERO Aug. 7, when astronaut and space pioneer Jim Lovell passed away at age 97. The first person to fly in space four times, Lovell helped pave the way for the first Moon landing and came to epitomize NASA’s can-do attitude. I had the honor and pleasure to interview Lovell three times during the latter half of the 2010s. Always gracious, humorous, and engaging, he became a good — dare I say it — friend. What follows is a remembrance, sprinkled with his reflections culled from our interviews. The early years James Arthur Lovell Jr. was born inCleveland on March 25, 1928. After his father died in a car accident in 1933, he and his mother moved to Terre Haute, Indiana, where they lived with…

THERE’S A WANING CRESCENT MOON three days past Last Quarter as the Geminid meteor shower peaks. While the Moon will subdue fainter meteors, the Geminids are well known for brilliant members and given that Gemini is very high near local midnight, meteors can be observed anywhere across the sky. The zenithal hourly rate is over 100, and the shower is regarded as the best one of the year, so even with the Moon around you should see quite a few meteors every hour. The second major shower in December is the Ursids, active from Dec. 17–26 and peaking the 22nd. There’s no interference from the Moon, although rates are one-tenth that of the Geminids. With the radiant up all night, however, there’s a good chance that you will spot some of…

COMET 24P/SCHAUMASSE rises around midnight, making it worthwhile to stay up late, especially on the weekend of the Geminids. On Friday the 12th, it shares a low-power field with NGC 3607 and 3608 (10th and 11th magnitude, respectively). With Schaumasse forecast at 9th to 12th magnitude, you can estimate its brightness easily. Use detailed charts to make sure you’re not misidentifying a background galaxy! Somewhat hampered by moonlight will be the “tilting knife” effect from Dec. 7–11. This is when Earth passes through the plane of the comet’s elliptical orbit, giving us an edge-on view of the dust fan. Any blue ion tail remains out of sight behind it. From country skies on the 25th, the comet is on the south side of M100 in a high-power field. Integrated magnitude can…

Observe from a table Celestron Torrance, California Celestron’s Moon Mission 100mm Tabletop Dobsonian is a 4-inch f/4 reflector. It comes with two eyepieces, a finder scope, and a Moon filter. The assembled unit weighs 5.3 pounds (2.4 kilograms), and the optical tube measures 14.2 inches (361 millimeters) long. $109.95 1-310-803-5955 www.celestron.com Complete system Explore Scientific Springdale, Arkansas Explore Scientific’s ED80-FCD100 Refractor is available in a kit that comes with a 0.8x focal reducer, changing the focal ratio of this 4-inch scope from f/6 to f/4.8. The company also includes its go-to mount, a 2.5-inch focuser, a 2-inch diagonal, and two counterweights. $1,399.98 1-866-252-3811 www.explorescientific.com Sharp view Tele Vue Optics Chester, New York The 19mm Nagler Type 7 eyepiece offers a mix of sharpness and correction. It contains seven lens elements,…

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The solar system’s two largest planets adorn the evening sky this month, while the smaller inner planets linger near the Sun and remain mostly out of sight. You’ll want to make Saturn your first target as darkness descends. The ringed planet shines at magnitude 1.0 and appears low in the west among the faint background stars of Pisces the Fish. Although Saturn stands 46° east of the Sun in early February, the ecliptic makes a shallow angle to the western horizon from mid-southern latitudes at sun-set this time of year, so the planet hangs low in our sky. The best views through a telescope come during fleeting moments of steady seeing. In mid-February, Saturn’s disk measures 16" across while the rings span 37" and tilt 3° to our line of…

This galaxy-studded view represents the deepest image ever of Abell 3667, a rich cluster of galaxies some 700 million light-years away. The composite image comprises 28 total hours of observations taken over the course of about a decade with the 570-megapixel Dark Energy Camera on the Víctor M. Blanco 4-meter Telescope in Chile. Just left of center is a glowing bridge of yellow starlight connecting Abell 3667’s two brightest galaxies, each of which represents the center of a smaller galaxy cluster. These two clusters are coming together to create one larger cluster. The so-called intracluster light is generated by stars stripped from the smaller of these two bright galaxies by its larger counterpart as they merge. Spanning about a million light-years, it is the largest such structure ever seen in…

RISING CARBON DIOXIDE (CO2) levels aren’t just affecting climate on Earth — they could also change the way our upper atmosphere responds to geomagnetic storms. This change could impact orbiting craft and services like GPS and satellite internet. Research published June 14 in Geophysical Research Letters modeled the response of the upper atmosphere to the same fierce solar storm in three future years — 2040, 2061, and 2084 — as levels of CO2 rose according to current high-emissions scenarios. The study focused on the thermosphere, which extends from about 50 to 440 miles (80 to 700 kilometers) above the planet. Although increasing CO2 near the surface causes temperatures to warm, it has a cooling effect on the thermosphere, causing this region to contract and leading to lower density over time. The…

ASTRONAUTS MIGHT BE BETTER OFF with robot medics — at least when it comes to CPR. French researchers simulating weightlessness on zero-gravity jet flights have found that manual cardiopulmonary resuscitation (CPR) is not effective in space, which could reshape emergency medical protocols for upcoming missions to the Moon and Mars. In weightlessness, simply pushing on a patient’s chest would send both rescuer and patient floating apart. So for decades, astronauts have been trained in a “handstand” technique where rescuers brace their feet against spacecraft walls. But in tests on training mannequins aboard parabolic flights, humans could achieve only 1.36 inches (34.5 millimeters) of compression depth, well below the suggested 1.97 to 2.36 inches (50 to 60 mm). On the other hand, Automatic Chest Compression Devices (ACCDs) consistently achieved the required…

Visible to the naked eye Visible with binoculars Visible with a telescope The long nights of December are an astronomical delight. The early evening sky hosts Saturn as the main feature, along with Uranus and Neptune. Jupiter rises later and is visible all night, its four main satellites undergoing many notable events. The morning sky shows the best Northern Hemisphere appearance of Mercury for the year. Let’s begin with Saturn and Neptune, 4.3° apart on Dec. 1. Saturn’s easterly motion carries it to within 3.5° of Neptune by the 31st. Saturn is easy to spot at magnitude 1.0 — the brightest object in the region except when the Moon passes by Dec. 26. Both planets stand 45° high in the southern sky as soon as it’s dark and set by…

TAKE A STROLL in the (star) fields to follow dwarf planet 1 Ceres. Fading from magnitude 8.5 to 8.9, the 600-mile-wide world won’t be a walk in the park, yet still easy enough from the suburbs with a 3-inch scope. You might want to start just east of Saturn and nail Neptune (magnitude 7.7) to calibrate your expectations. Gazers without motors can let Earth do the “hopping” in the first week of December. Center on magnitude 3.6 Iota (ι) Ceti, then come back eight minutes later to find Ceres sharing the field with a slightly brighter field star. Right through the 23rd, the background stars are fainter, with a reversal on the 24th when Ceres becomes component “B” of a double. New to charts and scopes? It’s best to make…

Q | WHY ARE THE JETS EMITTED BY BLACK HOLES OR NEUTRON STARS ALWAYS CONCENTRATED LIKE A LASER? Craig Case Twain Harte, California A | Astrophysical jets are rapid outflows from a central object that become focused into a narrow cone. Jets are everywhere in astrophysics: They occur near supermassive black holes like the 6-billion-solar-mass monster at the center of the giant elliptical galaxy M87 in Virgo (see the image at lower left) as well as near stellar-mass black holes, such as the more-than-10-solar-mass black hole in GRS 1915+105 in Aquila. Jets are found at neutron stars in supernova remnants like the famous Crab Nebula (M1), whose blast was seen in the year 1054, and also near neutron stars that draw mass from nearby companions, like Circinus X-1. Jets are…