comet – Watch the Skies

Ancient Oort Cloud Comet to Make First Documented Pass By Earth in Mid-October

An ancient celestial traveler will make its first close pass by Earth in mid-October. Mark those calendars – because it might not be back.

The Oort Cloud comet, called C/2023 A3 Tsuchinshan-ATLAS, was discovered in 2023, approaching the inner solar system on its highly elliptical orbit for the first time in documented human history. It was identified by observers at China’s Tsuchinshan – or “Purple Mountain” – Observatory and an ATLAS (Asteroid Terrestrial-impact Last Alert System) telescope in South Africa. The comet was officially named in honor of both observatories.

NASA astronaut Matthew Dominick captured this timelapse photo of Comet C/2023 A3 (Tsuchinshan-ATLAS) from the International Space Station as it orbited 272 miles above the South Pacific Ocean southeast of New Zealand just before sunrise on Sept. 28, 2024. At the time, the comet was about 44 million miles away from Earth. (NASA/Matthew Dominick)

The comet successfully made its closest transit past the Sun on Sept. 27. Scientists surmised it might well break up during that pass, its volatile and icy composition unable to withstand the intense heat of our parent star, but it survived more or less intact – and is now on track to come within approximately 44 million miles of Earth on Oct. 12.

“Comets are more fragile than people may realize, thanks to the effects of passing close to the Sun on their internal water ice and volatiles such as carbon monoxide and carbon dioxide,” said NASA astronomer Bill Cooke, who leads the Meteoroid Environment Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “Comet Ison, for example, reached the inner solar system in 2013, but failed to survive the Sun’s intense heat and gravity during perihelion in 2013.”

A bright green blur streaks across the black sky. — Comets traveling through the inner solar system aren’t uncommon, but many never survive a close pass by the Sun. Icy comet ISON, photographed here on Nov. 19, 2013, reached solar perihelion later that month – but couldn’t endure the punishing heat and gravity so close to Earth’s parent star and disintegrated. (NASA/MSFC/Aaron Kingery)

Though Comet Tsuchinshan-ATLAS will be ideally positioned to view from the Southern Hemisphere, spotters above the equator should have a good chance as well. Peak visibility will occur Oct. 9-10, once the half-moon begins to move away from the comet.

Choose a dark vantage point just after full nightfall, Cooke recommended. Looking to the southwest, roughly 10 degrees above the horizon, identify the constellations of Sagittarius and Scorpio. Tsuchinshan-ATLAS should be visible between them. By Oct. 14, the comet may remain visible at the midway point between the bright star Arcturus and the planet Venus.

“And savor the view,” Cooke advised – because by early November, the comet will be lost to the unaided eye, perhaps gone forever.

Comet light, comet bright

It’s highly unlikely Tsuchinshan-ATLAS will be visible in daylight hours, except perhaps at twilight, Cooke said. In the past 300 years of astronomical observation, only nine previous comets have been bright enough to spot during the day. The last were Comet West in 1976 and, under ideal conditions, Comet Hale-Bopp in 1997.

The brightness of comets is measured on the same scale we use for stars, one that has been in use since roughly 150 B.C., when it was devised by the ancient scholar Hipparchus and refined by the astronomer Ptolemy. Stellar magnitude is measured on a logarithmic scale, which makes a magnitude 1 star exactly 100 times brighter than a magnitude 6 star. The lower the number the brighter the object, making it more likely to be clearly seen, whether by telescope or the naked eye.

“Typically, a comet would have to reach a magnitude of –6 to –10 to be seen in daylight,” Cooke said. “That’s extremely rare.”

At peak visibility in the northern hemisphere, Tsuchinshan-ATLAS’s brightness is estimated at between 2 and 4. In comparison, the brightest visible star in the night sky, Sirius, has a magnitude of –1.46. At its brightest, solar reflection from Venus is a magnitude of –4. The International Space Station sometimes achieves a relative brightness of –6.

Comets are often hard to predict because they’re extended objects, Cooke noted, with their brightness spread out and often dimmer than their magnitude suggests. At the same time, they may benefit from a phenomenon called “forward scattering,” which causes sunlight to bounce more intensely off all the gas and debris in the comet’s tail and its coma – the glowing nebula that develops around it during close stellar orbit – and causing a more intense brightening effect for observers.

“If there is a lot of forward scattering, the comet could be as bright as magnitude –1,” Cooke said. That could make it “visible to the unaided eye or truly spectacular with binoculars or a small telescope.”

What will become of Comet Tsuchinshan-ATLAS? Cooke said it could be flung out of the solar system – like a stone from a sling – due to the gravitational influence of other worlds and a “jetting” effect caused by the comet’s offgassing during its solar transit.

But the hardy traveler likely still has miles to go yet. “I learned a long time ago not to gamble on comets,” Cooke said. “We’ll have to wait and see.”

Learn more about comets here.

Lane Figueroa
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
lane.e.figueroa@nasa.gov

Editor’s Note: The orbits of comets are continuously revised as new observational data becomes available. An earlier version of this article cited a period of 80,000 years for C/2023 A3 Tsuchinshan-ATLAS, which is no longer accurate based on newly available data. As of Oct. 14, the comet’s path may take it out of the solar system altogether.

Smith, an Aeyon employee, supports the Marshall Office of Communications.

When and How to Spot the ‘Devil Comet’

Comet 12P/Pons-Brooks is one of the brightest known periodic comets. It earned the nickname of “devil comet” in 2023 when an outburst caused the comet to have an asymmetrical appearance, like having horns. It comes around every 71 years and is currently getting brighter as it flies toward the Sun.

As spring approaches for northern skygazers, Comet 12P/Pons-Brooks is growing brighter. Currently visible with small telescopes and binoculars, the Halley-type comet could reach naked eye visibility in the coming weeks. Seen despite a foggy atmosphere, the comet's green coma and long tail hover near the horizon in this well-composed deep night skyscape from Revuca, Slovakia recorded on March 5. M31, also known as the Andromeda galaxy, and bright yellowish star Mirach, second brightest star in the constellation Andromeda, hang in the sky above the comet. The Andromeda galaxy is some 2.5 million light-years beyond the Milky Way. — As spring approaches for northern skygazers, Comet 12P/Pons-Brooks is growing brighter. Currently visible with small telescopes and binoculars, the Halley-type comet could reach naked eye visibility in the coming weeks. Seen despite a foggy atmosphere, the comet’s green coma and long tail hover near the horizon in this well-composed deep night skyscape from Revuca, Slovakia recorded on March 5. M31, also known as the Andromeda galaxy, and bright yellowish star Mirach, second brightest star in the constellation Andromeda, hang in the sky above the comet. The Andromeda galaxy is some 2.5 million light-years beyond the Milky Way.
**Image Credit & Copyright:** Petr Horálek / Institute of Physics in Opava

In the Northern Hemisphere, the comet is best viewed with binoculars or a small telescope – right after the Sun dips below the horizon, look West just beneath the Moon, and just right of Jupiter. An hour after sunset, the comet drops so low, it will be difficult to see without a perfectly clear view of the horizon. The comet then sets an hour later.

Sky chart showing the crescent Moon above Jupiter and Comet 12P in the western sky following sunset on April 10.
Credit: NASA/JPL-Caltech

Bill Cooke, who leads the Meteoroid Environment Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, encourages viewers to have more realistic expectations about what they might see. “Many images depict a bright comet with a long green tail,” Cooke said. “That’s not going to happen.”

By July, it will be too dim to view even with binoculars.

As for viewing this comet with the naked eye, it might be possible in the coming days, but by mid-April, it will be too close to the Sun and then growing fainter as it makes its way away from the Sun.

The brightest stars are a magnitude 1, the faintest are a magnitude 6. Comet 12P will peak around a magnitude 5 unless an outburst occurs.

However, Cooke warns that outbursts are unpredictable. “There have been minor outbursts roughly once a month but it’s impossible to predict them,” he said. “The last one was on Leap Day, Feb. 29.”

Will the comet be visible during the eclipse?

It is certainly a possibility. If Comet 12P remains around a magnitude 5, it would only be visible in binoculars during the few minutes of totality. Consider enjoying the main spectacle instead of using that time to locate Comet 12P and attempt to view it at another time.

For more skywatching highlights in April, check out Jet Propulsion Lab’s What’s Up series.

By Lauren Perkins
NASA’s Marshall Space Flight Center

New meteor shower? How many meteors will I see, really?

Astronomers are excited about the possibility of a new meteor shower May 30-31. And that excitement has sparked a lot of information about the tau Herculids. Some has been accurate, and some has not.

We get excited about meteor showers, too! But sometimes events like this don’t live up to expectations – it happened with the 2019 Alpha Monocerotid shower, for example. And some astronomers predict a dazzling display of tau Herculids could be “hit or miss.”

This infrared image from NASA's Spitzer Space Telescope shows the broken Comet 73P/Schwassman-Wachmann 3. — This infrared image from NASA’s Spitzer Space Telescope shows the broken Comet 73P/Schwassman-Wachmann 3 skimming along a trail of debris left during its multiple trips around the sun. The flame-like objects are the comet’s fragments and their tails, while the dusty comet trail is the line bridging the fragments. (Credit: NASA)

So, we’re encouraging eager skywatchers to channel their inner scientists, and look beyond the headlines. Here are the facts:

On the night of May 30 into the early morning of May 31, Earth will pass through the debris trails of a broken comet called 73P/Schwassmann-Wachmann, or SW3.
The comet, which broke into large fragments back in 1995, won’t reach this point in its orbit until August.
If the fragments from were ejected with speeds greater than twice the normal speeds—fast enough to reach Earth—we might get a meteor shower.
Spitzer observations published in 2009 indicate that at least some fragments are moving fast enough. This is one reason why astronomers are excited.
If a meteor shower does occur, the tau Herculids move slowly by meteor standards – they will be faint.

Observers in North America under clear, dark skies have the best chance of seeing a tau Herculid shower. The peak time to watch is around 1am on the East Coast or 10pm on the West Coast.

We can’t be certain what we’ll see. We can only hope it’s spectacular.

See Comet NEOWISE! A Once-in-a-Lifetime Event

For Comet Vocabulary, please read to the end of the post.

For most, early July is when most people living in the United States look to the skies to watch dazzling firework shows. However, this month there is a different kind of show happening in the sky.

Comet Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) was only discovered a few months ago on March 27 by NASA’s NEOWISE telescope and has quickly become a popular solar system visitor. Its popularity is warranted, however, as it is the brightest comet since Comet Hale-Bopp that passed by Earth 23 years ago in 1997.

The graphic shows the comet as seen from Huntsville, Friday, July 17 at 9 PM. Look almost due northwest, 15 degrees above the horizon. The comet will be below the stars in the bowl of the Big Dipper, and about as bright (magnitude 3). Binoculars should give a really spectacular view!

Comet nuclei are cosmic snowballs of frozen gases, rock and dust that orbit the sun. They can range in size from a few miles to tens of miles wide, and the nucleus of NEOWISE measures about 3 miles across. When these comets approach the sun, their frozen bodies start to sublimate, and they spew dust and gasses in a tail that can span millions of miles.

Comet NEOWISE made its harrowing close approach to the sun, known as its perihelion, on July 3, and it is now zooming past the Earth on its way back out of the solar system. NEOWISE will make its closest approach (64 million miles) to Earth on July 22, but the best viewing window is happening right now until July 19.

NEOWISE can be seen with the naked eye, but for an even better viewing experience, binoculars or even a telescope is recommended. As for which to choose, binoculars are your current best option. “Definitely use binoculars for now – the tail of NEOWISE is at least 7 degrees long, which is much bigger than the field of view of most telescopes,” said Bill Cooke, lead of NASA’s Meteoroid Environment Office at Marshall Space Flight Center. “Binoculars will allow you to see the whole thing, whereas a telescope only shows a tiny part.”

To see NEOWISE, start looking in the northwestern sky about an hour after sunset. The comet will be below the stars that make up the bowl of the Big Dipper and shining nearly as brightly at a magnitude 3. If you are an early riser, you can still see NEOWISE about an hour before sunrise in the northeastern horizon until the end of the week.

You need a clear view of the horizon to see this comet. Beaches, fields, and areas with higher elevations are all great observation spots. In areas with more light pollution, binoculars may be necessary for viewing. This is definitely a once-in-a-lifetime event, as NEOWISE won’t be visiting again for 6,800 years!

Learn more about comets at NASA’s Solar System Exploration website.

For comet-related, kid-friendly activities, visit NASA Science Space Place.

Comet Vocabulary

Comet – Made up of ice, dust and gas which form a coma and sometimes a visible tail when it is orbiting close to the sun

Nucleus – The head of the comet, which is made up of ice and frozen gas that vaporizes to form the coma and the tail

Sublimate – The transition of a substance directly from the solid to the gas state, without passing through the liquid state

Perihelion – The point where an object orbiting the sun is closest to the sun

Magnitude – The units used to describe brightness of astronomical objects. The smaller the numerical value, the brighter the object is

Rare Sights for Spring

As spring blooms in the Northern Hemisphere, here’s what’s happening in the night sky!

Venus
On April 3, Venus will pass near a star cluster known as the Pleiades. Also known as the Seven Sisters or M45, the Pleiades lies about 400 light years away from Earth, toward the constellation of the Bull — or Taurus.

Last year as Venus passed close to the Pleiades on June 9, the planet was five degrees south of the star cluster — 20 times farther away than it will be this year. Next year, Venus will be close to the star cluster once more on April 9 — this time at four degrees south of the Seven Sisters. This 2021 passing will be 16 times farther away than the 2020 event.

This year, viewers will have the rare chance at a brilliant view of Venus on April 3. With the naked eye, you will see something similar to the illustration below. However, the best view will be achieved through a pair of binoculars. Don’t miss your shot — Venus won’t make another appearance this close to the Pleiades until 2028!

This illustration -- generated by Bill Cooke using SkySafari Pro software -- captures what the naked eye might see as Venus passes through the Pleiades April 3, 2020. — This illustration — generated by Bill Cooke using SkySafari Pro software — captures what the naked eye might see as Venus passes through the Pleiades April 3, 2020.

Supermoon
We will have a Full Moon on April 7 at 9:35 p.m. CDT, at which time the Moon will be near to its perigee — or the point in its orbit that it is closest to Earth. This proximity will provide the largest appearance of the Moon for the whole year, commonly called a supermoon.

With the Artemis Program, NASA will land the first woman and next man on the Moon by 2024, using innovative technologies to explore more of the lunar surface than ever before. We will collaborate with our commercial and international partners and establish sustainable exploration by 2028. Until that day arrives, the supermoon will put us all a bit closer (physically) to our goal!

Comet C/2019 Y4 ATLAS
NASA astronomer Tiffany Clements recently captured the below image of Comet C/2019 Y4 ATLAS using a wide field telescope in New Mexico. Discovered at the end of December 2019 by an automated sky survey searching for Earth-approaching asteroids, this comet could brighten enough to be visible by late May or early June. However, comets are notoriously unpredictable, so stay tuned!

Comet C/2019 Y4 ATLAS (Credits: NASA/Tiffany Clements)

Bright Fireball Spotted Over Michigan

A bright fireball lit up skies over Michigan at 8:08 p.m. EST on Jan. 16, an event that was witnessed and reported by hundreds of observers, many who captured video of the bright flash.

Based on the latest data, the extremely bright streak of light in the sky was caused by a six-foot-wide space rock — a small asteroid. It entered Earth’s atmosphere somewhere over southeast Michigan at an estimated 36,000 mph and exploded in the sky with the force of about 10 tons of TNT. The blast wave felt at ground level was equivalent to a 2.0 magnitude earthquake.

The fireball was so bright that it was seen through clouds by our meteor camera located at Oberlin college in Ohio, about 120 miles away.

Events this size aren’t much of a concern. For comparison, the blast caused by an asteroid estimated to be around 65 feet across entering over Chelyabinsk, Russia, was equivalent to an explosion of about 500,000 tons of TNT and shattered windows in six towns and cities in 2013. Meteorites produced by fireballs like this have been known to damage house roofs and cars, but there has never been an instance of someone being killed by a falling meteorite in recorded history.

The Earth intercepts around 100 tons of meteoritic material each day, the vast majority are tiny particles a millimeter in diameter or smaller. These particles produce meteors are that are too faint to be seen in the daylight and often go unnoticed at night. Events like the one over Michigan are caused by a much rarer, meter-sized object. About 10 of these are seen over North America per year, and they often produce meteorites.

There are more than 400 eyewitness reports of the Jan. 16 meteor, primarily coming from Michigan. Reports also came from people in nearby states and Ontario, Canada, according to the American Meteor Society. Based on these accounts, we know that the fireball started about 60 miles above Highway 23 north of Brighton and travelled a little north of west towards Howell, breaking apart at an altitude of 15 miles. Doppler weather radar picked up the fragments as they fell through the lower parts of the atmosphere, landing in the fields between the township of Hamburg and Lakeland. One of the unusual things about this meteor is that it followed a nearly straight-down trajectory, with the entry angle being just 21 degrees off vertical. Normally, meteors follow a much more shallow trajectory and have a longer ground track as a result.

Shows the trajectory of the meteor. — This image shows the trajectory of the meteor as determined by the eyewitness accounts posted on the American Meteor Society Website. It is likely that there are meteorites on the ground near this region. (American Meteor Society)

NASA’s Short-term Prediction Research and Transition Center reported that a space-based lightning detector called the Geostationary Lightning Mapper — “GLM” for short — observed the bright meteor from its location approximately 22,300 miles above Earth. The SPoRT team helps organizations like the National Weather Service use unique Earth observations to improve short-term forecasts.

GLM is an instrument on NOAA’s GOES-16 spacecraft, one of the nation’s most advanced geostationary weather satellites. Geostationary satellites circle Earth at the same speed our planet is turning, which lets them stay in a fixed position in the sky. In fact, GOES is short for Geostationary Operational Environmental Satellite. GLM detected the bright light from the fireball and located its exact position within minutes. The timely data quickly backed-up eyewitness reports, seismic data, Doppler radar, and infrasound detections of this event.

Data from NOAA's GOES-16 space-based weather satellite — Data from NOAA’s GOES-16 space-based weather satellite detected a bright flash of light over southeast Michigan around the time a meteor entered Earth’s atmosphere. (NASA/SPoRT)

Much like the nation’s weather satellites help us make decisions that protect people and property on Earth, NASA’s Meteoroid Environment Office watches the skies to understand the meteoroid environment and the risks it poses to astronauts and spacecraft, which do not have the protection of Earth’s atmosphere. We also keep an eye out for bright meteors, so that we can help people understand that “bright light in the night sky.”

596 Scheila: An Identity Crisis?

Things are getting a little stranger in the asteroid belt these days! Objects in this zone of the solar system are known to be rocky bodies, though in the past few years several of these bodies have had cometary features detected. One such body is 596 Scheila, which has always been confidently called a main-belt asteroid, meaning it is a rocky body orbiting nicely between Mars and Jupiter causing no trouble to Earth.

Scheila is 113 km in diameter and was discovered in 1906 by August Kopff in Heidelberg and named after an acquaintance of the discoverer. For the past 104 years Scheila has been pleasantly orbiting without much fuss until last week the Catelina Sky Survey found a coma around the object with a 0.68 meter Schmidt telescope; quickly confirmed by many other observers.Scheila, along with several other bodies in the past few years, have created a new class of solar system objects: main-belt comets. Main-belt comets have the orbital characteristics of main-belt asteroids, but exhibit an outgassing, comae, or a dust-tail that is normally seen on icy comets that came from the outer-reaches of our solar system. These bodies are an anomaly and a mystery since an object this close to the sun should have had its ices vaporized away. This has caused another theory to arise that perhaps they are not icy bodies, but perhaps the trail of debris was caused by an asteroid-asteroid collision.

3200 Phaethon, the parent body of the famous Geminid meteor shower, is another example of this. Phaethon was always thought to be an asteroid, a purely rocky body, and even its meteoroids agreed with this, being denser than an average icy-meteoroid. But in recent times Phaethon has exhibited dust-outgassing, causing observers to wonder whether it once was a comet, or if it has had a recently collision to cause the particles.

Unlike Phaethon, Scheila will not intersect Earth’s orbit and thus we will not have a Scheilid meteor shower. Whether this outgassing and dust production from asteroids is due to vaporization of earth or asteroid collisions, only time will tell. Oh, the mysteries of our solar system!

Orbit of 596 Scheila, as computed by the JPL small-body database browser.

Image of 596 Scheila using a V Filter and 10 stacked images of three-minute exposures each.

Image of 596 Scheila using an R Filter and 10 stacked images of three- minute exposures each.

Images were taken via a remote-operated camera located in New Mexico. Stars are trailed because the asteroid was being tracked. You can clearly see the fuzzy “cloud” or coma about the asteroid in the center.

Images courtesy of Bill Cooke and Rhiannon Blaauw, NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala.

Ikeya-Murakami: The New Comet on the Cosmic Block

The animation below shows the motion of Comet Ikeya-Murakami on Nov. 13, 2010, captured with a New Mexico-based telescope operated remotely by NASA’s Marshall Space Flight Center. The images were taken near dawn and show the comet’s movement over a period of 45 minutes. Each exposure was three minutes in length, and the faint angled streak around 0:10 in the animation is a satellite trail. At the time of these images, the comet was some 229 million miles away from Earth.

Comet Ikeya-Murakami was discovered very recently on Nov. 3, 2010, by Japanese amateur astronomers Kaoru Ikeya and Shigeki Murakami. Their discovery is unusual because they both used manual observations through optical telescopes to identify the comet. Such observations are rare in recent times when astronomers use cutting-edge digital imaging to study the skies.

Ikeya-Murakami is classified as a long-period comet, or those comets having eccentric orbits ranging from 200 years millions of years to make one circuit around the sun.

Courtesy of Rob Suggs, NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala.

Only 11.5 Million Miles Away Now!

MSFC astronomer Bill Cooke took this five-minute exposure of Comet Hartley 2 late on the night of Saturday, Oct. 16, 2010, using a 10″ telescope in New Mexico.

The comet, which has now reached naked eye visibility, was just under 11.5 million miles from Earth and sporting a coma over a degree across — twice the size of the full moon. You can read more about the “coma” and other parts of a comet at the NASA Worldbook: Comets page.

This very active visitor to our neighborhood makes its closest approach around 8 a.m. EDT on Oct. 20, at a distance of 11.2 million miles. Unfortunately, the light from the nearly full moon will tend to wash out the comet’s pale green glow, so comet watchers are advised to make use of a pair of binoculars for the best view.

Image courtesy of Bill Cooke, NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala.

Camel Leopards and Comets

Camelopardalis.

It’s a strange-sounding name for a constellation, coming from the Greco-Roman word for giraffe, or “camel leopard”. The October Camelopardalids are a collection of faint stars that have no mythology associated with them — in fact, they didn’t begin to appear on star charts until the 17th century.

Even experienced amateur astronomers are hard-pressed to find the constellation in the night sky. But in early October, it comes to prominence in the minds of meteor scientists as they wrestle with the mystery of this shower of meteors, which appears to radiate from the giraffe’s innards.

The October Camelopardalids are not terribly spectacular, with only a handful of bright meteors seen on the night of Oct. 5. It may have been first noticed back in 1902, but definite confirmation had to wait until Oct. 2005, when meteor cameras videotaped 12 meteors belonging to the shower. Moving at a speed of 105,000 miles per hour, Camelopardalids ablate, or burn up, somewhere around 61 miles altitude, according to observations from the NASA allsky meteor cameras on the night of Oct. 5, 2010.

So they aren’t spectacular. Their speed is calculated. Their “burn up” altitudes and orbits are known. So what’s the mystery?

Camelopardalids have orbits, which indicates that they come from a long period comet, like Halley’s Comet. But the Camelopardalids don’t come from Halley, nor from any of the other comets that have been discovered. Hence the mystery: somewhere out there is — or was — a comet that passes close to Earth which has eluded detection. These tiny, millimeter size bits of ice leaving pale streaks of light in the heavens are our only clues about a comet of a mile, maybe more, in diameter.

This is why astronomers keep looking at the Camelopardalids meteors. They hope that measuring more orbits may eventually help determine the orbit of the comet, enabling us to finally locate and track this shadowy visitor to Earth’s neighborhood.