Comet C/2024 G3 ATLAS may put on a quick show this month.
Comet G3 ATLAS on December 30th. Credit: Alan C. ToughWhat ‘may’ be the best anticipated comet of 2025 is coming right up. Right now, there’s only one comet with real potential to reach naked eye visibility in 2025: Comet C/2024 G3 ATLAS. This comet reaches perihelion at 0.094 Astronomical Units (AU, 8.7 million miles or 14 million kilometers, interior to the orbit of Mercury) from the Sun on January 13th, and ‘may’ top -1st magnitude or brighter. At magnitude +4 in late December, Comet G3 ATLAS could become a fine object low in the dawn sky for southern hemisphere observers… if (a big ‘if) it holds together and performs as expected.
The comet actually produced an outburst over the first weekend of 2025, jumping from magnitude +4 to +1 (a sixteen-fold increase in brightness in a few short days). This could be a harbinger for good (or bad) things to come shortly.
“The comet has had an outburst in the last few days,” Nicolas Lefaudeux told Universe Today. “If the outburst is linked to disintegration, there would probably be nothing to see after perihelion. If the outburst is linked to new active areas or splitting of a large nucleus, the display could be much better than in the simulations.”
The prospects for the tail of Comet G3 ATLAS, around perihelion. Credit: Nicolas LefaudeuxA recent International Astronomical Union Central Bureau for Astronomical Telegrams message suggests an optimistic peak of -3rd magnitude near perihelion post outburst, ‘if’ the comet holds together.
Comet G3 ATLAS low at dawn versus Mercury on January 11th. Credit: Starry Night. The DiscoveryThe comet was discovered by the Asteroid Terrestrial-Impact Last Alert System (ATLAS) survey as a +19th magnitude object in the southern hemisphere constellation Apus the Bee on the night of April 5th, 2024.
The orbital path for Comet G3 ATLAS through the inner solar system. Credit: NASA/JPLThe orbital period for this one is around 160,000 years. It’s unclear if Comet G3 ATLAS is a first-time visitor to the inner solar system, or a new denizen coming from the distant Oort Cloud. The last time the comet swung by the inner solar system (assuming it has done so in the past), wearing clothing was the hot new thing among our homo sapiens ancestors.
Comet G3 ATLAS from January 2nd. Credit: iTelescope/Tara Prystavski. Comet G3 at Perihelion: Perish or Prosper?Prospects for seeing this comet will be tricky. Unlike last year’s Comet C/2023 A3 Tsuchinshan-ATLAS which unfurled a magnificent tail for its evening apparition, G3 ATLAS will be a timid one both before and after perihelion, as it departs our solar neighborhood hugging the southern horizon in the dusk sky.
Comet G3 ATLAS, post perihelion on January 15th at dusk. Credit: Starry Night.A daytime comet could be in the offing if G3 ATLAS over-performs at perihelion… but it will be a challenging view, very near the Sun. Be sure to block the dangerous glare of the Sun fully out of view behind a building or structure if you attempt to spot the comet in daylight. Like A3 T-ATLAS, the joint NASA/ESA SOHO observatory will see the comet near perihelion crossing through its LASCO C3 viewer.
Comet G3 ATLAS versus SOHO through the month of January. Credit: Starry Night. Best Bets For Comet G3 ATLASPerihelion on Monday, January 13th, 2025 will see the comet just four degrees from the Sun. The comet also makes its closest approach to Earth at 0.938 AU distant on the same date. The comet ‘could’ reach -4th magnitude (about as bright as Venus) around the same time… if it manages to hold together at perihelion.
Here’s a recent remote telescope image of the comet taken from late December by Nick James:
Comet G3 ATLAS from December 15th. Credit: Nick James/BAA Comet Section/iTelescope.Comet G3 ATLAS has been elusive thus far. The comet has been bashful, skimming just five degrees above the dawn horizon leading up to perihelion in early January for northern hemisphere observers. The comet reemerges low to the west after dusk, but again, folks up north only get a very brief view 5-10 degrees above the horizon at dusk, as the comet runs parallel with the horizon southward. As usually seems to be the case with comets, the southern hemisphere gets the better view.
Here’s a blow-by-blow of what to expect in the coming months from the comet. (Note that ‘passes near,’ denotes a conjunction of a degree or less):
January6-Near the Lagoon Nebula (Messier 8)
7-Near the globular cluster (Messier 28)
8-Crosses the ecliptic plane northward
11-Enters SOHO LASCO C3 view
13-At perihelion, less than 5 degrees from the Sun
14-Crosses into the constellation Capricornus
15-Exits SOHO LASCO C3 view, and crosses the ecliptic plane southward
21-Nicks the corner of the constellation Microscopium
22-Crosses into the constellation Piscis Austrinus
The light curve for comet G3 ATLAS. Adapted from Seichii Yoshida’s Weekly Information About Bright Comets. February1-May drop back down below +6th magnitude
6-Crosses into the constellation Grus
21-Nicks the corner of the constellation Sculptor
25-Crosses into the constellation Phoenix
MarchMarch 1st: May drop back down below +10th magnitude.
Observing and imaging the comet will be challenging, owing to two main factors: first, it will never really leave the low-contrast, twilight sky for northern hemisphere observers. Second, said quoted magnitude for a comet gets ‘smeared out’ over its apparent surface area, knocking the comet’s apparent brightness down a notch or two. We can hope that Comet G3 ATLAS is an over-performer in this regard. My strategy is to find high ground to observe from and the lowest, flattest horizon (like, say, the ocean as seen from a beach) that you can find, and sweep the horizon at low power with binoculars for the fuzzball of a comet.
Good luck and clear skies on this, the first comet quest of 2025.
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One powerful way to study the galaxies is to study individual stars. By looking at the ages, types, and distribution of stars in the Milky Way, we’ve captured a detailed snapshot of how our galaxy formed and evolved. The only problem with this approach is that we can only do this for a handful of galaxies. Even with the most powerful telescopes, we can only see individual stars in the Milky Way and nearby galaxies such as Andromeda. For galaxies billions of light years away, individual stars blur together, and the best we can do is observe the overall spectra of galaxies, not individual stars. But thanks to a chance alignment, we can now observe dozens of stars in a galaxy so distant we see it at a time when the Universe was half its present age.
The results are published in Nature Astronomy, and they focus on JWST observations of a cluster of galaxies known as Abell 370. This galactic cluster is famous because it acts as a gravitational lens for more distant galaxies behind it. You can see them as arcs of light in the image above. One prominent arc, highlighted in the image, is known as The Dragon. It is made up of the lensed and magnified images of several galaxies, the light of which has traveled 5 to 7 billion years to reach us.
The Dragon has been studied before using observations from the Hubble Space Telescope, and from these studies astronomers have been able to see a handful of blue supergiant stars, which are the largest and brightest main sequence stars. But identifying individual stars is notoriously difficult. In this new study, the team used JWST observations of The Dragon from 2022 and 2023. Since the Webb is capable of capturing high-resolution images in the infrared, it’s perfectly suited to study the spectra of redshifted stars in the cosmic middle age.
Individual stars identified in the Dragon arc in 2022 and 2023. Credit: Yoshinobu Fudamoto, et alBut even the Webb would be hard-pressed to identify more than a few bright stars within The Dragon, were it not for a second effect of gravitational lensing known as microlensing. Within the distant galaxy, two stars can line up just so, and the more distant star is gravitationally magnified for a short time, like a flare. This allows astronomers to study the spectra of the distant star. So a galaxy from 7 billion years ago is lensed into a bright arc of light by the Abell 370 cluster, and within that galaxy stars are further microlensed by a stellar alignment.
The team was able to identify more than 40 microlensing events, and was therefore able to capture the spectra of more than 40 individual stars in the distant galaxy. Based on the spectra, these stars are red supergiants similar to Betelgeuse. The study shows that microlensing events such as these are common, so we should be able to see lots more stars in this distant galaxy in the future.
We know a great deal about red supergiants in the Milky Way. Since they are dying stars, red giants play a significant role in enriching the available elements in a galaxy, which determines things such as the formation of stars and even life. But by studying these distant red giants, we will be able to see how they impacted the chemical diversity of younger galaxies. It could even help us understand what the Milky Way was like when the Sun and Earth began to form.
Reference: Yoshinobu Fudamoto, et al. “Identification of more than 40 gravitationally magnified stars in a galaxy at redshift 0.725.” Nature Astronomy (2025).
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Getting a spacecraft to another star is a monumental challenge. However, that doesn’t stop people from working on it. The most visible groups currently doing so are Breakthrough Starshot and the Tau Zero Foundation, both of whom focus on a very particular type of propulsion-beamed power. A paper from the Chairman of Tau Zero’s board, Jeffrey Greason, and Gerrit Bruhaug, a physicist at Los Alamos National Laboratory who specializes in laser physics, takes a look at the physics of one such beaming technology – a relativistic electron beam – how it might be used to push a spacecraft to another star.
There are plenty of considerations when designing this type of mission. One of the biggest of them (literally) is how heavy the spacecraft is. Breakthrough Starshot focuses on a tiny design with gigantic solar “wings” that would allow them to ride a beam of light to Alpha Centauri. However, for practical purposes, a probe that small will be able to gather little to no actual information once it arrives there—it’s more of a feat of engineering rather than an actual scientific mission.
The paper, on the other hand, looks at probe sizes up to about 1000kg—about the size of the Voyager probes built in the 1970s. Obviously, with more advanced technology, it would be possible to fit a lot more sensors and controls on them than what those systems had. But pushing such a large probe with a beam requires another design consideration—what type of beam?
Fraser discusses how we might get to Alpha Centauri.Breakthrough Starshot is planning a laser beam, probably in the visible spectrum, that will push directly on light sails attached to the probe. However, given the current state of optical technology, this beam could only push effectively on the probe for around .1 AU of its journey, which totals more than 277,000 AU to Alpha Centauri. Even that minuscule amount of time might be enough to get a probe up to a respectable interstellar speed, but only if it’s tiny and the laser beam doesn’t fry it.
At most, the laser would need to be turned on for only a short period of time to accelerate the probe to its cruising speed. However, the authors of the paper take a different approach. Instead of providing power for only a brief period of time, why not do so over a longer period? This would allow more force to build up and allow a much beefier probe to travel at a respectable percentage of the speed of light.
There are plenty of challenges with that kind of design as well. First would be beam spread—at distances more than 10 times the distance from the Sun to the EartSunhow would such a beam be coherent enough to provide any meaningful power? Most of the paper goes into detail about this, focusing on relativistic electron beams. This mission concept, known as Sunbeam, would use just such a beam.
Fraser discusses another interstellar probe – Project DragonflyUtilizing electrons traveling at such high speeds has a couple of advantages. First, it’s relatively easy to speed electrons up to around the speed of light—at least compared to other particles. However, since they all share the same negative charge, they will likely repel each other, diminishing the beam’s effective push.
That is not as much of an issue at relativistic speeds due to a phenomenon discovered in particle accelerators known as relativistic pinch. Essentially, due to the time dilation of traveling at relativistic speeds, there isn’t enough relative time experienced by the electrons to start pushing each other apart to any meaningful degree.
Calculations in the paper show that such a beam could provide power out to 100 or even 1000 AU, well past the point where any other known propulsion system would be able to have an impact. It also shows that, at the end of the beam powering period, a 1,000kg probe could be moving as fast as 10% of the speed of light – allowing it to reach Alpha Centauri in a little over 40 years.
Multi-stage ships could be the key to interstellar travel – as Fraser discusses.There are plenty of challenges to overcome for that to happen, though – one of which is how to get that much power formed into a beam in the first place. The farther a probe is from the beam’s source, the more power is required to transmit the same force. Estimates range up to 19 gigaelectron volts for a probe out at 100 AU, a pretty high energy beam, though well within our technology grasp, as the Large Hadron Collider can form beams with orders of magnitude more energy.
To capture that energy in space, the authors suggest using a tool that doesn’t yet exist, but at least in theory could – a solar statite. This platform would sit above the Sun’s surface, using a combination of force from the push of light from the star and a magnetic field that uses the magnetic particles the Sun emits to keep it from falling into the Sun’s gravity well. It would sit as close as the Parker Solar Probe’s closest approach to the Sun, which means that, at least in theory, we can build materials to withstand that heat.
The beam forming itself would happen behind a massive sun shield, which would allow it to operate in a relatively cool, stable environment and also be able to stay on station for the days to weeks required to push the 1000kg probe out as far as it would go. That is the reason for using a statute rather than an orbit—it could stay stationary relative to the probe and not have to worry about being occluded by the Earth or the Sun.
Fraser discusses interstellar travel with Avi Loeb, a Harvard professor and expert in interstellar travel.All this so far is still in the realm of science fiction, which is why the authors met in the first place – on the ToughSF Discord server, where sci-fi enthusiasts congregate. But, at least in theory, it shows that it is possible to push a scientifically useful probe to Alpha Centauri within a human lifetime with minimal advances to existing technology.
Learn More:
Greason & Bruhaug – Sunbeam: Near-Sun Statites as Beam Platforms for Beam-Driven Rockets
UT – Researchers are Working on a Tractor Beam System for Space
UT – A Novel Propulsion System Would Hurl Hypervelocity Pellets at a Spacecraft to Speed it up
UT – A Concentrated Beam of Particles and Photons Could Push Us to Proxima Centauri
Lead Image:
Depiction of the electro beam statite used in the study.
Credit – Greason & Bruhaug
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