Observable comets in 2024, from Guy Ottewell

Overhead view of the orbit of Earth. The sun is in the middle of the orbit. The paths of two comets are visible. One passes by the orbit of Earth, the other one crosses between the sun and the orbit of Earth.
This space view shows the paths of 2 observable comets in 2024: C/2021 S3 PANSTARRSS and C/2023 A3 Tsuchinshan-ATLAS. They are the first 2 comets in the list below. The ecliptic plane (the plane of Earth’s orbit around the sun) is indicated by grid lines at intervals of 1 AU (astronomical unit, or 1 Earth-sun distance). The thicker line is the vernal equinox direction (zero point for celestial mapping). The viewpoint is 6 AU from the sun, 35 degrees north of the plane, at ecliptic longitude 35 degrees. Stalks from the comets to the plane are at 1-month intervals. Sightlines from Earth to the comets are drawn at dates of opposition, that is, when the comets are opposite the sun as seen from Earth and visible in the midnight sky. Earth is exaggerated 500 times in size, the sun only 5 times. The comets themselves – their solid nuclei, that is – would be vanishingly small. Chart via Guy Ottewell. Used with permission.

Observable comets in 2024

UK astronomer Guy Ottewell published his article about comets in 2024 at his website on January 12, 2024. Reprinted with permission. Edits by EarthSky.

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Comets are always unpredictable

The predicted brightness of a comet – an icy visitor, often from the outermost reaches of our solar system – can and does change frequently. For example, a comet’s orbital elements can change, as observations are continually sent in by observers around the world. Or, a comet’s brightness parameters may be changed. The brightness predictions are based on a comet body’s size (typically around six miles, or 10 km, in diameter) and the rate at which it brightens by shedding cloudy material as it approaches the sun.

Also, new comets can and do appear from the depths of space.

So comets don’t always behave as we think they will! That said, my calculations suggest the comets in the chart below will be brighter than 9th magnitude in 2024. That is, they’ll be bright enough to observe with binoculars or small telescopes in dark sky.

Chart listing 5 comets that might be observable in 2024 with data about the declination, magnitude and elongation for each comet.
Note the column labeled “mag.” In the logarithmic magnitude scale, smaller numbers indicate brighter objects. So, 1st magnitude is brighter than 2nd magnitude. The unaided-eye threshold is about 5th or 6th magnitude depending on sky conditions. So 2 of these 5 comets might reach that higher threshold, though uncomfortably close to the sun. The others should be findable with binoculars and small telescopes, in a dark sky. The column for “dec” shows approximate declination (like latitude on the sky’s dome, indicating how far north or south they are in the sky). And “elo” stands for elongation, in degrees. Negative elongation (–) means westward, so they will be visible in the morning sky. Chart via Guy Ottewell. Used with permission.

More about this chart

Just so you know … the above list of observable comets – and their brightnesses or magnitudes – can change at any time.

See the note at the bottom of this post to learn how I calculated 2024’s observable comets. After disentangling my calculations, I find these comets might be brighter than magnitude 9.5 in 2024. In other words, these are the comets you might see with ordinary 7X50 binoculars. And, if we’re lucky, some of these comets could become visible to the eye alone.

By the way, the 9.5 magnitude threshold is arbitrary. Changing it admits more or fewer comets. Also, there is always the caution that their actual behavior can depart wildly from what’s predicted. That’s because comets can flare, or shed so much of their cloudy material that they become like asteroids. Or comets can break into several bodies, and completely disintegrate and disappear. Never bet on a comet! Additionally, there are often new comets of the non-periodic kind, which are unpredictable and are liable to be among the brightest. These can arrive from deep space at any time.

Comet 62P Tsuchinsha

62P Tsuchinsha’s designation means that it was the 62nd comet to be recognized as periodic – that is – with elliptical orbit of under 200 years. And it was at its brightest for 2024 on January 1, 2024. That’s because it passed its peak brightness on December 25, 2023. However, reports are that it may be running about one magnitude brighter than predicted and is currently shining around magnitude nine.

It will be nearest to Earth (0.495 AU) on January 29, 2024, but half a magnitude dimmer because it’s farther from the sun. And then, it will keep climbing higher in the morning sky until we pass it at opposition on March 24. Unfortunately, it will probably have faded to magnitude 12 by then.

Dark sky with many white dots in the background. There are bigger whote dots in the foreground, they are united by lines. The moon on the right. A tail at the top, right of the image.
Chart showing the position of Comet 62P Tsuchinshan on January 29, 2024, when its closest to Earth. It’ll be in the constellation of Virgo the Maiden. Click here for charts and information based on your location, date and time. Chart via The Sky Live.

Comet C/2021 S3 PANSTARRSS

C/2021 S3 PANSTARRSS was one of the discoveries of the automated search program Pan-STARRS (Panoramic Survey Telescope and Rapid Response System, on Mount Haleakala in Hawaii). And S3 means it was the third comet discovery or recovery in the second half of September. By the way, it approached us from the south, in a vast and steeply inclined orbit (eccentricity given as 1.0002, inclination 58.5 degrees).

So, in contrast to 62P, it is running fainter than the prediction. It will cross the ecliptic plane northward on February 7, 2024, and pass through perihelion (closest to the sun, 1.32 AU, not far outside Earth’s orbit) on February 14. Then, around February 28, it should be at its brightest, about magnitude seven. Afterward, it’ll cross the celestial equator northward on March 4 and be nearest to Earth (1.29 AU) on March 14. Later, by the end of May it’ll be around magnitude 10. Finally, in August, when it’s at opposition (2.5 AU away from us) and far north in the sky, it’ll probably be a dim magnitude 12.

Chart with the path of comet C/2021 S3 Panstarrss as a yellow line. There are stars and constellations around.
Here is a chart for comet C2021-S3-PANSTARRSS as it travels across the sky dome in February 2024 almost along the plane of the Milky Way. We draw comets’ tails schematically, to suggest the direction in which they are driven outward by radiation pressure from the sun; they may or may not be as large as shown. Chart via Guy Ottewell Used with permission.

Comet 12P/Pons-Brooks

Comet 12P/Pons-Brooks is a periodic comet (a comet that has an orbit around the sun less than 200 years) discovered by Jean-Louis Pons in 1812 and then recovered by William Robert Brooks in 1883. It orbits the sun every 71 years. At perihelion – or its closest approach to the sun – it will be about 0.78 astronomical units (AU) from the sun. Its aphelion – or its furthest point from the sun – is about 17.2 AU from the sun.

In 2024 Comet 12P/Pons-Brooks is predicted to become bright enough to see with the unaided eye. Coincidentally, it’ll be closest to the sun about two weeks after the total solar eclipse on April 8 2024. So there is a chance observers may be able to see the comet during totality.

Starry sky white white dots conected by red lines. There is a trail at the top right of the image.
Chart showing Comet 12P/Pons-Brooks on April 21, 2024, when its closest to the sun. It’ll be in the constellation of Taurus the Bull. Click here for charts and information based on your location, date and time. Chart via The Sky Live.

Comet 13P/Olbers

13P/Olbers is a periodic comet with an orbital period of 69 years. The comet was last seen in 1956 and its next perihelion (closest point to the sun) is on June 30, 2024. It’ll be 1.18 AU from the sun and is expected to be shining at around magnitude 7.5.

Starry sky with white dots conected by red lines. There is a bright tail in the top center of the image.
Chart showing location of Comet 13P/Oblers on June 30, 2024. Click here for charts and information based on your location, date and time. Chart via The Sky Live.

One of the brightest comets in 2024?

And, last but not least, we may have a bright comet in October 2024. Indeed, we are long overdue for a beautiful comet with a wispy comet tail stretching across our evening sky. In October 2024, especially around October 14 through 24, C/2023 A3 (Tsuchinshan-ATLAS) could be bright in the early evening sky. With ten months to go, all looks good for a great showing.

The comet will make its closest approach to the sun perihelion on September 28, 2024. At that point, some estimates are suggesting it might be around magnitude 0.7. That brightness rivals some of the brightest stars in the sky (though, for comets, the brightness is diffuse, not in a single point). Stay tuned!

Star chart showing a comet with tail pointing away from the horizon for 2 dates, 1 closer to the horizon and 1 higher up.
If we are fortunate, a comet will grace our sky from October 14 to 24, 2024. Look to the west shortly after sunset for Comet Tsuchinshan–ATLAS. Chart by John Jardine Goss/ EarthSky.

Note from Guy Ottewell

The reason “hairy stars” have been absent from the last few Guy Ottewell’s Astronomical Calendars is because it was difficult to find information far enough in advance about comets likely to be observable.

I used a list of orbital elements for comets provided by the Minor Planet Center and ran calculations for the whole year to find which of them should become observable. The only criterion I’ve used is brightness (astronomically expressed as magnitude).

However, other factors can affect observability: elongation (angular distance from the sun) and declination (how far north or south in the map of the sky).

Bottom line: Here are predictions from Guy Ottewell for the observable comets in 2024. C/2023 A3 Tsuchinshan-ATLAS may be a bright comet in October 2024.

January 18, 2024

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