Astronomy

Comets have long been seen as omens and portents, and it’s easy to understand why. They first appear as faint smudges of light in the sky, sometimes fading soon after and sometimes becoming brighter than the planets, with a long, glowing tail. They have been observed throughout human history, but it wasn’t until the eighteenth century that astronomers began to predict the return of some comets. Even today, we can’t predict the return of most comets until after they swing through the inner solar system. If such a comet happens to be heading toward Earth, we wouldn’t know about it until too late. But that could change thanks to our observations of meteor showers.

Comets originate from the Oort cloud, the icy remnant of our solar system’s birth that surrounds the Sun as a sphere 100,000 AU in diameter. Whether through a close collision with another Oort object or the nearby passing of a star, some of these distant chunks of ice and rock are sent tumbling toward the inner solar system. They can come from any direction in the sky, and once they dance near the Sun they may not return for hundreds or thousands of years. Any comet with a period longer than 200 years is known as a long-period comet, and these are the hardest to predict.

Most long-period comets pose no threat to Earth. They might appear bright in the evening or morning sky, but their orbits don’t cross Earth’s orbit, so there is no risk of impact. But some long-period comets could pose an impact threat to Earth. We know this in part because we’ve been hit by comets before, and in part because we observe regular meteor showers. Showers such as the Geminids, Perseids, and Orionids are caused by the dusty trails left by comets as they cross Earth’s orbit. In these cases, we have even identified the originating comets as Phaeton, Swift-Tuttle, and Halley’s. But of these, only Swift-Tuttle is a long-period comet (barely) with an orbital period of 257 years.

Illustration of long-period comets and the Oort cloud. Credit: National Astronomical Observatory of Japan

These connections between comets and meteor showers were made by first knowing the comet’s orbit then connecting its path to known showers. In principle, we should be able to do it the other way around. Identify what the path of a meteor shower is, and then use that to search for its long-period comet. As new telescopes such as Rubin Observatory come online, this approach could become a useful tool in the search for impact threats. A recent study on the arXiv shows how this would work.

The team ran simulations of long-period comets ranging from 200 to 4,000 years. They estimated the dust trails these hypothetical comets would produce, then set out to determine if astronomers could use these trails to work backwards to locate the originating comet while it is far from the Sun. In anticipation of having high-resolution sky surveys, the team assumed astronomers could observe them at the anticipated resolution of Rubin Observatory. They found that the orbits of many comets don’t produce showers useful for prediction, but in 17 cases, the showers could be used to identify comets months or years before they would typically be noticed.

The expected orbit for the Aurigid shower. Credit: Hemmelgarn, et al

To prove this point even further, the team also looked at a meteor shower called the ?-Hydrids, a faint shower that appears in early December. The origin of the sigma-Hydrids was not known until the appearance of Comet Nishimura in 2023. Once the orbit was determined, astronomers found a possible connection to the sigma-Hydrid showers. Using known observations of the shower before 2023, the team was able to determine a possible orbit for the comet. They found that with a Rubin-like sky search, astronomers could have found Nishimura eight months before its actual discovery.

Reference: Hemmelgarn, Samantha, et al. “How Meteor Showers Can Guide the Search for Long Period Comets.” arXiv preprint arXiv:2410.02883 (2024).

The post Astronomers Predict the Orbits of Potentially Hazardous Comets From Meteor Showers appeared first on Universe Today.

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A geomagnetic storm, the largest supermoon of the year, a comet and an eerie fireball were among the skywatching treats that haunted the night sky of October 2024.

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Comet C/2023 A3 Tsuchinshan-ATLAS survived perihelion to become a fine dusk object for northern hemisphere observers.

It was an amazing month for astronomy. Not only were we treated to an amazing second solar storm for 2024 that sent aurorae as far south as the Caribbean, but we had a fine naked eye comet: C/2023 A3 Tsuchinshan-ATLAS.

The comet on October 24th, along with the Milky Way over the Sea of Japan as seen from Yuzhno-Morskoy (Nakhodka) Russia. Credit: Filipp Romanov.

Discovered in early 2023, this one actually performed as expected, and topped out as the best comet for 2024. Southern hemisphere observers got a portent of things to come in September, as the comet threaded the dawn skies.

The evolution of the comet post-perihelion through October 25-30th. Credit: Eliot Herman Peril at Perihelion

Then came the big wild card of perihelion. The comet passed just 58.6 million kilometers from the Sun on September 27th. At its maximum, the comet hit nearly -5th magnitude. The dust and plane crossing for the comet were both especially dramatic, as we saw a sharp spiky anti-tail trace out the comet’s orbital trail and appear to pierce the Sun as seen in views from SOHO’s LASCO C2 and C3 imagers.

But would the comet remain bright for its evening encore? This time, luck was on our side, as the comet held at +1st magnitude for about a week, and joined Venus in the dusk sky. As it began its rapid ascent, Comet ‘T-ATLAS’ unfurled its tail about a dozen degrees in length, all while keeping its remarkable anti-tail pointing sunward.

The comet from October 18th, still exhibiting a spiky ‘anti-tail. Credit: Efrain Morales. A ‘Just Point-and-Shoot’ Comet

And then the pictures came pouring in. Comet T-ATLAS was at its photogenic best in early October, as it became an easy target against the starry backdrop. Usually, +2nd magnitude or brighter is the cutoff for catching a comet along with foreground objects. This time, you could actually simply set your smartphone camera to night mode, and capture a decent handheld shot of the comet.

The comet from October 19th, as seen from Ottawa, Canada. Credit: Andrew Symes

Plus, light pollution didn’t seem to faze this comet. We saw shots of the comet from downtown Los Angeles and other urban areas, as folks were treated to the best comet in recent memory since the dawn apparition of F3 NEOWISE in 2020.

Venus, a meteor, an airplane trail, and Comet T-ATLAS from Malaysia. Credit: Shahrin Ahmad.

And to think: the last time a really brilliant comet swung by (C/1995 O1 Hale-Bopp a generation ago in 1997) digital imaging was in its infancy, and film still dominated the market… just think what we might manage to do with such a comet today?

“I drove north for more than three hours, and reached the seashore facing the Sea of Japan after sunset,” says astrophotographer Hisayoshi Kato on Flickr, “It was fortunate that the sky was clear at the site, and I could enjoy the comet sinking into the Sea of Japan (over) the weekend.”

Comet C/2023 A3 Tsuchinshan-ATLAS from October 26th. Credit: Hisayoshi Kato. Awaiting Next ‘Great Comet’

To be sure, it’s only a matter of time before the next ‘Comet of the Century’ makes itself known. Right now, Comet T-ATLAS is still a decent +6th magnitude binocular object in Ophiuchus, outbound on its nearly quarter-of-a-million-year orbit. Alas, a second sungrazer encore for October never came to pass, as Comet C/2024 S1 ATLAS ended its cometary career at perihelion earlier this week…

An amazing parting shot of the comet from October 29th. Credit: Gianluca Masi.

“These days, we all had an extraordinary proof of the splendor of the night sky,” astronomer Gianluca Masi noted in a recent Facebook post. “Comet C/2023 A3 Tsuchinshan-ATLAS is still putting on a show… but the firmament is always a prodigy of emotions and wonders, as those who regularly turn their gaze to the stars know.”

Comet T-ATLAS from downtown Bristol, Tennessee. Credit: Dave Dickinson.

When’s the next one? Well, we do have the promise of a similar comet coming right up in January 2025. C/2024 G3 ATLAS may reach -1st magnitude or brighter near perihelion.

Thanks to everyone that got out there and sent images to the Universe Today Flickr pool. Here’s to the next yet-to-be named bright comet, waiting in the wings to take center stage in the drama of the inner solar system and the skies of Earth.

The post Amazing Reader Views of Comet A3 Tsuchinshan-ATLAS From Around the World appeared first on Universe Today.

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One of my favorite paintings is Starry Night by Vincent van Gogh — for obvious astronomical reasons. But another favorite of van Gogh’s works is Lane of Poplars at Sunset. This painting depicts the setting Sun perfectly aligned with a long lane of trees, casting long shadows.

The geometry of the Earth and Sun means that this scene had to be painted on one specific day of the year when the alignment would be possible. An astronomer has now used 19th-century maps to discover where the lane was, and then used astronomical calculations to determine which date the Sun would be in the exact position as the painting. His result? The painting depicts a stretch of road known as Weverstraat in the Dutch town of Nuenen, on November 13 or 14, 1884.

Professor Donald Olson is an astronomer and physics professor emeritus at Texas State University (TSU). He is no stranger to studying van Gogh paintings, as in the past he has uncovered clues to help date three other of the noted painter’s works: Moonrise (July 13, 1889), Road with Cypress and Star (May 1890) and White House at Night (June 1890).

Van Gogh produced more than 2,000 paintings, drawings, and sketches in his lifetime, and many include scenery from The Netherlands, the Dutch master’s home. Olson was originally inspired to determine the date of Lane of Poplars at Sunset because the scene shows something similar to what happens twice a year for New York City’s “Manhattanhenge,” where the setting sun aligns with Manhattan’s east–west streets on dates near May 29 and July 12.  

Manhattanhenge from 42nd Street shot at 8:23 p.m. on July 13, 2006, the building on the right is the Chrysler Building. Photo by Roger Rowlett, via Wikipedia.

The first thing Olson wanted to figure out was where the lane might be.

“If we could identify the lane on 19th-century maps, then we’d be able to establish the compass direction of the road appearing in the artworks,” Olson explained in a news release from TSU. “Next, we could use astronomical calculations to determine the date when the disk of the setting sun aligned as van Gogh portrayed it.”

Olson called in assistance from Louis Verbraak and Ferry Zijp, members of the Eindhoven Weather and Astronomy Club in the Netherlands. After an exhaustive search of maps and correlating historic and recent imagery, the team narrowed it down to three possible streets. Further investigations led them to determine that Weverstraat in Nuenen must be the street, as it contained a long straightaway of 1,200 feet, or 365 meters, more than long enough for the scene painted by van Gogh.

As for determining the date, Olson and team relied on historical information. All of van Gogh’s paintings assigned catalog numbers, in order by dates determined by art historians. Lane of Poplars at Sunset is assigned as F123. The previous painting in the catalog, F122, is called Lane of Poplars in the Autumn, which shows the same scenes with vivid fall colors, while the leaves are almost completely gone from the trees in the sunset depiction. That means the painting had to be done in late fall.

The painting “Line of Poplars in Autumn” by Vincent van Gogh (F122, Nueun 1884).

Art historians have also long depended on van Gogh’s many letters to his brother Theo to help date most of the artist’s work. A total of three letters, written by Vincent during late October and early November of 1884, describe the lovely autumn weather he was experiencing. One letter, dated on or about Oct. 25, 1884, includes a description that matches Lane of Poplars in the Autumn:

“The last thing that I made is a rather large study of a lane of poplars with the yellow autumn leaves, where the Sun makes glittering patches here and there on the fallen leaves on the ground, alternating with the long shadows cast by the trunks. At the end of the road is a peasant cottage, and above it the blue sky between the autumn leaves.”

“White House at Night” by Vincent van Gogh. (F766 Auvers-sur-Oise, 1990).

A subsequent letter dated on or about Nov. 14, 1884, van Gogh indicated that freezing weather forced him to abandon painting outdoors for the rest of the season. Additional letters helped establish a time frame between Nov. 5-Nov. 14 for van Gogh to have painted Lane of Poplars at Sunset. Within this range of dates, planetarium software shows that the sun set in the southwest, in the range of azimuths, or compass direction of a celestial object, between 240° and 244°.

Then using astronomical calculations, Olson and team determined the setting sun would’ve been visible setting over Weverstraat on Nov. 13 or 14, 1884. Historical weather records indicate these dates fall within a five-day span where the area experienced unseasonably clear weather.

Olson said that because van Gogh rarely painted from memory and preferred to have his subject in front of him, Nov. 13 or 14, 1884, are the only possible dates for the creation of Lane of Poplars at Sunset.

“Today, we can still gaze down the same stretch of road where van Gogh walked on a chilly autumn afternoon and ponder how the artist, in his native Netherlands, was already interested in portraying sky phenomena, four years before he began to create his famous starry nights in the south of France,” Olson said.

Read more details about the search at TSU.

The post Astronomer Calculates When van Gogh Painted This appeared first on Universe Today.

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