Comet C/2021 A1 Leonard was first detected on January 3, 2021 by Greg Leonard with the 1.5 m telescope of the Mount Lemmon Survey, in Arizona (USA).
It was then at a distance of 5 astronomical units (roughly equivalent to the distance between Jupiter and the Sun) ; it already had a magnitude of about 19.
It is a long-period comet : about 83 000 years and it is probably not at its first passage near the Sun.
Its apparent movement in the sky is fast (up to 10° per day). Its retrograde orbit (with an inclination of 133°) explains the brevity of its passage near the Earth.
Trajectory
From early December to mid-December, the comet exits the constellation of the Hounds to cross the Cattle Dog, before entering the Snake.
The conditions are particularly favorable in this period, because the sky is free of Moon and the brightness of the comet is increasing. It is currently a little brighter than magnitude 6.
As a reminder, comet C/2020 F3 NEOWISE, which was the comet of the summer of 2020, had reached magnitude 6 and was visible in the Paris region with the naked eye.
A closer to the Earth...
Its closest passage to the Earth is scheduled for December 12, when it will be located at 0.23 astronomical units.
On December 13, 2021, it will be visible mainly in the morning twilight, before its conjunction with the Sun.
Between December 13 and 16, around the conjunction, at 15-20° from the Sun, the comet will probably be difficult to see at dawn, but the very high phase angle (160°) could enhance its brightness by more than one magnitude through forward scattering on the dust.
After these dates until the end of December, the comet will become observable in the southern hemisphere, but as it will darken in the direction of the Sun, it will be increasingly difficult to observe : it will be quickly drowned in the dawn light.
Note that on December 18, at 2 am, it will pass very close to Venus (at 0.029 astronomical unit) and will be located in the sky at 6° from the planet, the evening before.
One year to the day after its discovery, on January 3, 2022, the comet will be at perihelion, that is to say, at the closest point to the Sun at a distance of 0.615 astronomical units.
It will then return to its birthplace, the Oort cloud, at the edge of the Solar System. It is foreseeable that it leaves the Solar System definitively because, at its passage near the perihelion, it will gain slightly in speed to leave on a slightly deviated orbit.
| [Observing campaign From December 8 to 13, 2021, astrophysicists observe comet C/2021 A1 Leonard with the radio telescope of the radio astronomy station in Nançay and the 30 m radio telescope of the IRAM. The observations will continue with the ALMA radio telescope of ESO in Chile. |