On October 9, 2023, China’s Guangzhou Observatory reported that the C/2023A3 (Zijingshan-Atlas) comet will come closest to Earth on October 12, reaching a periapsis of 0.47 astronomical units, or approximately 70 million kilometers away. After sunset, stargazers in China will have another chance to observe and capture the breathtaking beauty of this comet in the southwestern sky.

This comet passed its perihelion on September 27, boasting its longest tail during that time. Many astronomy enthusiasts in China were able to witness and photograph the comet just before sunrise in late September through early October.

The C/2023A3 comet was first identified on January 9, 2023, by the Xuyi Observatory in Nanjing, and subsequently received its designation. The “C” indicates that it is a non-periodic or long-period comet, the year 2023 marks its discovery, “A” refers to the first half of January, and “3” signifies it as the third comet discovered in that period.

Experts explain that comets orbit the Sun in elliptical, parabolic, and hyperbolic paths. When a comet’s eccentricity, defined as its “flattening,” is less than 1, it follows an elliptical path; at exactly 1, it follows a parabolic path; and if greater than 1, it follows a hyperbolic path. Elliptical orbits are closed curves, associated with periodic comets, while the other two paths are open curves, typically relating to non-periodic comets that do not return after leaving the Sun. Over the last 300 years, astronomers have tracked over 600 cometary orbits, discovering that approximately 40% follow elliptical paths, while about 60% are either parabolic or hyperbolic. Halley’s Comet, for example, has an eccentricity of 0.967 and completes an orbit roughly every 76 years, classifying it as a short-period comet.

The C/2023A3 comet moves in an almost parabolic elliptical orbit with an eccentricity close to 1, with an orbital inclination of about 139 degrees and a cycle of approximately 61,751 years. When comets approach larger celestial bodies, they can undergo “gravitational perturbations,” altering their speed and potentially transitioning from periodic to non-periodic classifications. Therefore, whether humanity will see this comet again remains uncertain.

From October 12 to 20, 2023, enthusiasts will have prime opportunities to observe and photograph the C/2023A3 comet. It will be brightest on October 12, with an apparent magnitude of about 2, although it will be positioned quite low on the horizon. The comet’s tail will point eastward, moving away from the Sun. After this date, while the comet will rise higher in the sky, its brightness will decrease. Just after sunset, Venus will appear low in the southwestern sky, providing a dazzling sight just north of the comet.

For the best viewing experiences, lower latitude regions in southern China offer better conditions compared to the north. To observe and photograph the comet effectively, experts recommend finding locations away from city light pollution, aiming for places where stars of magnitude 4 can be easily seen at night, and seeking unobstructed western vistas free of tall buildings, trees, or mountains.

For observing, telescopes or binoculars can be utilized, with photography best done using a tripod. Employing an equatorial mount, photographers can capture exposures lasting from several seconds to minutes, revealing celestial bodies otherwise invisible to the naked eye. When using a camera, set the aperture to its maximum, adjust to a suitable ISO sensitivity, and use a shutter speed generally less than 5 seconds. Focus on Venus when composing shots, then adjust the framing to include both Venus and the comet.