Great comets, or comets with great visual magnitude or brightness, are not just visible to the naked eye; they often outshine the most brilliant stars in the night sky. Their tails, composed of dust and gas, can stretch vast distances, sometimes spanning a significant portion of the sky.
More often than not, great comets have left an indelible mark on human history. From being perceived as omens of change (both good and bad) to inspiring art, literature, and even religious interpretations, their brilliance extends beyond the night sky. They can be associated with the birth or death of leaders, such as Julius Caesar, or as omens of bad events.
Great comets are usually long-period or non-periodic comets, the type of comet originating from the Oort Cloud—a vast, spherical region of icy bodies located almost a light-year from the sun. From a scientific standpoint, these comets are of utmost interest as they offer insights into the early Solar System. Their infrequent visits near the sun and Earth mean that they are relatively pristine, containing unaltered material from the time of the solar system’s formation.
The appearance of a great comet is a relatively rare event, occurring perhaps once or twice in a decade at best. This infrequency further amplifies their significance and allure. The most recent comet that most would define as a “Great Comet” was Comet McNaught in 2007, preceded by the pairing of Hyakutake in 1996 and Hale-Bopp just a year later. McNaught was mostly visible from the Southern Hemisphere, meaning Northern Hemisphere observers have (as of the time of writing) waited more than 25 years for a new great comet.
However, comet C/2020 F3 (NEOWISE) in 2020 arguably deserves the title of “great comet” in the eyes of many. Comet NEOWISE was visible to the unaided eye for a substantial period around mid-2020, and thanks to reduced light pollution from COVID lockdowns, the comet was unusually prominent even to city dwellers. However, NEOWISE was not visible in the daytime; its tail stretched just a few degrees across the sky, and while visible to the naked eye for over a month, it was still far from obvious to most viewers, particularly from light-polluted locales.
When is the Next Great Comet?
No one really knows when the next “great comet” will be. As of the time of writing, C/2023 A3 (Tsuchinshan-ATLAS) looks promising to be the next comet visible from earth. If it doesn’t fizzle, the comet’s best period of visibility will be September–November 2024, when the comet is near its closest approach to both the Sun and Earth. Tsuchinshan-ATLAS will be best viewed from the Northern Hemisphere, and the large size estimates for its icy nucleus mean that it is possible, but by no means guaranteed, that this comet could be easily visible to the naked eye at its closest approach, perhaps even in the daytime. However, comets such as Kohoutek in 1976, ISON in 2012, and C/2022 E3 (ZTF) in 2023 were similarly hyped up, only to be barely visible to the naked eye at best.
