If you expect to give, or receive, a smart telescope for the holidays, you may want to arrange for it to be unwrapped now so you can catch a glimpse of an unusual visitor—the interstellar comet 3I/ATLAS. The comet is closest to Earth this Friday, Dec. 19. It’ll still be visible for a few weeks into January, but after that, it disappears from our skies forever.
I have photographed 3I/ATLAS in the predawn sky on a dozen occasions using a pair of tiny smart telescopes placed on the windowsill of my New York City apartment. Even as it slowly fades as it recedes from the Sun, 3I/ATLAS is easy enough to pick up using even these basic, relatively low-priced scopes—for now.
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An Interstellar Wanderer, Just Passing Through
Comet 3I/ATLAS was discovered on July 1 by the ominous-sounding Asteroid Terrestrial-impact Last Alert System (ATLAS) automated sky survey, which has found 112 potentially hazardous asteroids and 111 comets, including 2024’s brilliant Tsuchinshan-ATLAS. (I will refer to the interstellar comet as either 3I or 3I/ATLAS, to distinguish it from the numerous other comets ATLAS.) Astronomers soon determined, by its rapid speed and its path, that it came from beyond our solar system, only the third such interstellar comet to be confirmed, and easily the brightest, despite not coming particularly close to either the Earth or the Sun.
At discovery, 3I/ATLAS was in eastern Sagittarius. It is unknown what star system it originated in; it may have been wandering the Milky Way for billions of years, possibly even longer than the Earth and Sun have existed. When closest to the Sun in late October, passing just outside the orbit of Mars, 3I was behind the Sun and invisible from our vantage, although several spacecraft orbiting Mars and even a rover on the Red Planet’s surface observed it. Despite claims that 3I is really an alien spaceship, it has looked and behaved like a comet, with some variations in its chemical composition, as would be expected from an object that originated in a different star system under unknown conditions.
Sleuthing Out Comet 3I/ATLAS With a Smart Telescope
By mid-November, 3I had emerged from the solar glare into the predawn sky. I began photographing it using two tiny smart telescopes—astronomical cameras controlled through iPad apps—arranged side by side on my windowsill. The ZWO Seestar S30 ($349) is a smaller version of the Editors’ Choice-winning Seestar S50 ($549), which I reviewed in 2024. I am currently reviewing the DwarfLab Dwarf 3 ($549) for PCMag. They are simple to set up and use; in addition to comets, they can image other objects, including the Sun (a solar filter is included), the Moon, galaxies, nebulae, and star clusters. You can also use them for birding and other nature photography.
With some smart telescopes, including DwarfLab scopes, it is easy to use their apps to locate 3I/ATLAS. It appears in the Unistellar app’s Catalog in its list of comets, though you may have to tap on Visible Sky Area to show it. Searching for “3I” in the Celestron Origin app takes you to a descriptive page in the comet from which you can slew to it. With the Dwarf 3, from the Atlas page in Deep Sky mode, you can find it by tapping the magnifying glass and entering “3I.”
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Once the scope finds the comet, you can set parameters such as exposure length and gain (I use 60), let it take dark exposures if prompted, and then press the red button on the right side of the screen to begin the series of shots.
3I/ATLAS, taken with the Dwarf 3 near a faint asteroid, 55 Pandora (Credit: Tony Hoffman)
Finding 3I/ATLAS is a bit more involved when using the Seestar app. The app includes a list of currently observable comets, but 3I is not among them. (The list is based on a formula for predicted brightness rather than actual brightness.) To find 3I, tap the SkyAtlas button on the bottom toolbar, touch the magnifying glass icon labeled Objects. Typing in “3I” should reveal a record for the comet, listing its current altitude. Tapping on the crosshairs icon should reveal the comet’s position in the SkyAtlas. If the scope is powered up and connected to the app (the Seestar has a built-in Wi-Fi hotspot), tapping the go-to button instructs the scope to slew to the comet and start imaging. Pressing the red button at the bottom of the screen stops the exposure.
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Comet 3I Atlas with the Seestar S30, 10 minutes of stacked 10-second frames (Credit: Tony Hoffman)
Smart telescopes photograph most celestial objects by taking a series of exposures and virtually stacking the images, reducing noise and bringing out more detail; you can watch the emerging image on your tablet or smartphone’s screen. I use 10-second exposures for the S30 and 15-second ones for the Dwarf 3, and have generally gone for a total exposure time of between 6 and 10 minutes. In less than a minute, 3I/ATLAS’s image appears, resembling a small, fuzzy patch with a star-like center. After about 10 minutes, the comet’s image becomes notably oblong due to 3I’s motion through the sky. (You could also try longer exposures to illustrate this motion.)
Comet 3I/Atlas is unassuming as comets go; its renown is that it’s an interstellar comet making its only passage through our solar system. I’ve observed more than 50 comets and photographed maybe 35, and although many have looked more spectacular, I’ve gotten a particular thrill out of photographing this one. But even if you miss 3I, or find it underwhelming, there are other, more visually stunning comets you can image with a smart telescope; Comet Lemmon, which I photographed in October, was a particularly nice one.
Comet Lemmon, taken with the Seestar S50 in October (Credit: Tony Hoffman)
Although 3I/ATLAS is at its closest this week, it is still far away from us, nearly twice the distance between the Earth and the Sun. It is moving through southern Leo, and a few days after Christmas will pass near the bright star Regulus. By Jan. 22, a much-faded 3I will be in Cancer, opposite the Sun in our sky and visible all night. It will continue its lonely trek into the depths of space, heading toward a point near the Gemini-Orion border as it moves onward, out into the galaxy.
About Our Expert
Tony Hoffman
Senior Writer, Hardware
Experience
Since 2004, I have worked on PCMag’s hardware team, covering at various times printers, scanners, projectors, storage, and monitors. I currently focus my efforts on 3D printers, pro and productivity displays, and drives and SSDs of all sorts.
Over the years, I have reviewed smart telescopes, iPad and iPhone science apps, plus the occasional camera, laptop, keyboard, and mouse. I’ve also written a host of articles about astronomy, space science, travel photography, and astrophotography for PCMag and its past and present sibling publications (among them, Mashable and ExtremeTech), as well as for the former PCMag Digital Edition.
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