Gregory J. Leonard, an astronomer working at the Mount Lemmon Observatory near Tucson, Arizona, discovered the first long-period comet of the year, C/2021 A1 Leonard. At the time of its discovery, it had a brightness of +19 magnitude and was 5 astronomical units from Earth (about the distance between Jupiter and the Sun).
In an 80,000-year orbit, Comet Leonard A1 will leave the solar system after passing through perihelion early next year. The comet reached a distant point in the Oort Cloud about 35,000 years ago, at a distance of 3,500 AU. The perihelion to be passed on January 3, 2022, will be 0.62 AU from the Sun, located inside the orbit of Venus.
A1 Leonard may be a long-term visitor to the inner solar system, with the potential for brightness to spike as it approaches the Sun. The current prediction is that the comet will be more than 4 rated, and it may reach a level that can be observed by the naked eye. The comet was only 0.233 AU (21.7 million miles or 34.9 million kilometers) from Earth when it passed earth on December 12.
For observers in the Northern Hemisphere, A1 Leonard is located in the constellation Scorpio at dawn and begins to fall rapidly toward the sun in the first half of the month. We will pass through the comet's orbital plane on December 8, and the comet may exhibit a sharp inverted tail at this time, tilting toward the sun.
Another intriguing effect could also occur in December, when from December 9 to December 22, the Sun-Earth-Comet's phase angle will be greater than 120 degrees, and reach its maximum of 160 degrees on December 14, just as it passes closest to Earth on December 12. This creates the ideal conditions for a luminance surge, reflecting the brightness of the tail onto the comet itself.
On December 19, Venus will pass through the tail of Comet A1 Leonard, potentially producing a meteor shower of Venus in the process. Currently, only the Akatsuki probe of the Japan Aerospace Exploration Agency is active in orbit around Venus. Unfortunately, around December 15, comet A1 Leonard was observed from morning to dusk, and for observers in the northern hemisphere, the comet stays low at dusk. However, observers in the southern hemisphere will have a better view as the comet fades away and retreats to the direction of the constellation ostrinus in early 2022.