remembering-the-comet-of-the-yearhttps://www.astronomy.com/observing/remembering-the-comet-of-the-year/Remembering Comet Tsuchinshan-ATLAS: The comet of the yearTsuchinshan-ATLAS was that rare type of comet that arrived with fanfare and lived up to the hype, serving up naked-eye views for weeks.https://www.astronomy.com/uploads/2025/04/ASY-TA0525_05-1568x571.jpgInStockUSD1.001.00cometsarticleASY2025-05-052025-05-05161161
The Milky Way serves as a proscenium arch for the zodiacal light and Comet Tsuchinshan-ATLAS in this panorama taken Oct. 19 near Cerro Pachón in the Chilean Andes. The photographer used a Canon 6Da DSLR and a 20mm f/1.4 lens to take twelve 8-second frames at ISO 1600. Credit: Lucas Thibaud
Comets are notoriously unpredictable. Some of the most spectacular of these icy visitors pop up unexpectedly, careening toward the Sun and bursting out in spectacular fashion with little advance notice. Others are spotted over a year before they make their closest approach, but break apart and fizzle out.
Comet Tsuchinshan-ATLAS was the rare comet that arrived with a year and a half of fanfare and lived up to the hype, serving up naked-eye views for weeks. If it was not a Great Comet, it was at least a very, very good one.
Formally known as C/2023 A3, this ice ball from the outer solar system was first discovered in images taken Jan. 9, 2023, by a telescope operated by Purple Mountain Observatory near Nanjing in China’s Jiangsu Province. A month and a half later, it was identified by a telescope in South Africa belonging to the Asteroid Terrestrial-impact Last Alert System (ATLAS). These observations put the object at 670 million miles (1.1 billion kilometers) from the Sun, between the orbits of Jupiter and Saturn.
It wouldn’t reach perihelion — its closest point to the Sun — until Sept. 27, 2024. But immediately, the gears of the hype machine began turning. Initially, it appeared that the best views could wind up being exclusive to the Southern Hemisphere. The comet first became visible in the southern predawn sky, and remained low in the northern sky as it reached perihelion. Soon after, it moved into conjunction with the Sun and was lost in our star’s glare. But the best views were yet to come: The comet reemerged as an easy naked-eye evening object around the same time it made its closest approach to Earth on Oct. 12. At its peak, it was recorded as bright as magnitude –4.9, the brightest in the Northern Hemisphere since 1997’s Hale Bopp (C/1995 O1). Tsuchinshan-ATLAS also sported a stunning tail stretching up to 15° in photographs, plus a stark anti-tail.
Comets being what they are, there’s no telling when one this bright will swing by next. Until then, we have these images to savor.
As Comet Tsuchinshan-ATLAS approached, it first graced the Southern Hemisphere with pre-dawn naked-eye views. This shot was taken from Farm Tivoli in Namibia on Sept. 30, 2024, a few days after perihelion. Credit: Gerald RhemannComet Tsuchinshan-ATLAS appears above the ridgeline of the Diablo Range in this Sept. 28 shot taken from Lick Observatory, California. The photographer captured the comet in a tracked 10-second exposure at ISO 100 with an astromodified Nikon mirrorless camera and a 200mm zoom lens at f/2.8. Credit: Abhijit PatilThe comet’s long tail appears in this 30-second shot taken from Caçapava, São Paulo, Brazil. The photographer used a Nikon DSLR and 50mm lens at f/2.2 and ISO 250. Orbits of long-period comets like Tsuchinshan-ATLAS cannot be predicted precisely, but on its current course, it won’t return for around 80,000 years. Credit: Jean CursinoPainters Point near Carmel-by-the-Sea in Monterey County, California, lies beneath the Milky Way and Comet Tsuchinsan-ATLAS in this 18-panel mosaic taken Oct. 22, 2024. Each panel of sky consists of a 30-second exposure taken with an astromodified Nikon Z 6II mirrorless camera at ISO 3200, a zoom lens at 24mm and f/2.8, and a UV/IR cut and Hα bandpass filter. Credit: Abhijit PatilA trio of Orionid meteors accompany Comet Tsuchinshan-ATLAS in this Oct. 21 composite photo taken from Singalila National Park in West Bengal, India, at an altitude of more than 7,000 feet (2,100 m). The photographer used a Panasonic mirrorless camera and lens at 35mm, capturing the comet with twenty-four 8-second frames at f/4 and ISO 6400. Separate stacks were captured for the starlight and foreground. Credit: Soumya BanerjeeComet Tsuchinshan-ATLAS mingles with the stars and spotlights above the Hollywood Hills in this image taken from Griffith Park in Los Angeles on Oct. 12, 2024. The photographer used an iPhone 14 Pro to take a 10-second exposure. Credit: Nasir JeevanjeeThe comet shares the frame with the Milky Way and satellite streaks over the mountains outside Salt Lake City. This image is a 60-second exposure taken with a Canon DSLR and 14mm lens at f/2.5 and ISO 1600. Credit: Martin RatcliffeThe comet’s dust and ion tails blend in a combination of orange and blue hues in this shot taken Oct. 14 from Piano Vetore on the southern flank of Mount Etna at an elevation of 5,700 feet (1750 m). The image comprises 25 minutes of exposure with a 2.4-inch refractor and cooled CMOS camera. Credit: Aldo Rocco VitaleA sinuous ion tail and brilliant dust tail are on display in this shot taken Sept. 30, three days after reaching perihelion. This image was captured with a combination of DSLR and astronomical cameras in LRGB filters. Credit: Gerald Rhemann/Michael Jäger/Dennis MöllerThe comet developed a needlelike anti-tail — a secondary tail that appears to protrude from the comet’s nucleus in the opposite direction of the “normal” tails, as pictured here Oct. 17. An anti-tail is a perspective effect created when dust left behind in the comet’s orbit appears to point toward the Sun. The imager used a CMOS camera and 135mm lens at f/2.8 to take LRGB exposures totaling 10, 2, 2, and 2 minutes, respectively. Credit: Alessandro Carrozzi
What’s in a name?
A Perseid meteor streaks behind the dome of Purple Mountain Observatory’s Xuyi Station, the first facility to detect Comet C/2023 A3. Credit: Hao Liu
Comet Tsuchinshan-ATLAS owes its name to two observatories that discovered it independently. The first, Purple Mountain Observatory (PMO), was founded in 1934 and is considered China’s first modern astronomical observatory. The name Tsuchinshan — traditionally used for comets discovered by PMO — is an older transliteration of Zijinshan, which is Chinese for “purple mountain.” The observatory’s historic location is atop a mountain in the heart of Nanjing, a city of nearly 10 million people.
The Minor Planet Center’s code for the observatory is Nanking — the historic transliteration of Nanjing. But the bulk of PMO’s research is now conducted at several satellite observatories at more remote sites. The telescope that first detected Comet C/2023 A3 is a 1.2-meter Schmidt located in Xuyi County, roughly 30 miles (50 kilometers) northwest of PMO’s original site. The Xuyi station reported three detections of the object over a single night, but it was subsequently presumed lost.
The Asteroid Terrestrial-impact Last Alert System (ATLAS) is an network of four telescopes operated by the University of Hawai’i and funded by NASA that scans the entire sky in search of asteroids that could threaten Earth. Two ATLAS scopes are in Hawaii, one is in Chile, and one is in South Africa. The latter — a 0.5-meter Schmidt at the South African Astronomical Observatory in Sutherland — is the one that independently detected Comet C/2023 A3, on Feb. 22, 2023. Subsequent analysis revealed that it was the same object discovered by PMO.
