The big tail disconnection


C/2021 A1 (Leonard)




R.A. 21 h 10 m 10 s Dec. -33° 45′ 04″



Distance from Sun: 

96 million km

Distance from Earth:

89 million km

Apparent size:

Coma: 6'; tail: 4° (PA: 95°)



Sidereal period:



53 km/s




25/12/2021 18:35-18:39 UT

Total exposure time:

3 minutes


Skygems Remote Observatories - Hakos, Khomas, Namibia


QHY 600M


Officina Stellare Veloce 200/600 mm RH AT







Focal ratio, length:

f/3, 600 mm






1 x 60 s R/G/B








Astro Pixel Processor, PixInsight, Adobe Lightroom, Adobe Photoshop



Location in the Solar System

C/2021 A1 (Leonard) - 25/12/2021
(Robotic telescope)

Main object: C/2021 A1 (Leonard)

In 2021, we were not without a bright comet, but this was a very different experience to the one we had for weeks with the naked eye, C/2020 F3 (NEOWISE). We had time to prepare ourselves for this comet, unlike the wanderer that arrived in 2020.

Gregory J. Leonard spotted the comet on 3th of January 2021, and it was predicted to brighten, making it a highly observable celestial object for the inhabitants of the northern hemisphere. But at the time, no one could have guessed that a few weeks later, observers in the southern hemisphere would be treated to a very different quality of experience when the comet arrived.

Unfortunately, the autumn and winter weather in the Carpathian Basin is not usually a spoiling time for astronomy enthusiasts, and this time was no different: in the first half of December 2021, the binocular-observable wanderer was seen less than five times.

We were not lucky with the weather at dawn on 3th of December 2021, when the comet apparently "hit" the M3 globular cluster from Earth. The next day, the sky cleared and the comet was seen by a large number of Hungarian observers. The round coma of Leonard's comet, green in colour due to the presence of diatomic carbon molecules, was clearly distinguishable from the thin tail of the comet, which was more than 1 degree long. Its activity has stagnated during these days, holding steady to predictions and perhaps even declining, with a brightness of only around 6.5 magnitude.

The comet's closest approach to Earth was on 12th of December 2021 (35 million kilometres away), but by then its much more favourable dawn visibility had already deteriorated significantly. For a few days, it was visible in the twilight sky below Venus, but later it was only visible from southern countries. The last time many of Hungarians saw the comet on 17 December 2021, we had no idea that the real show would begin.

The comet had produced a small outburst earlier, but what happened on 20th of December 2021 caught the attention of many. The wanderer produced an increase in brightness of several magnitude, meaning it crossed the boundary of naked-eye visibility. The astrophotographers reacted immediately, booking the southern robotic telescopes one after the other. The C/2021 A1 (Leonard) comet grew an incredibly long and spectacularly structured gas tail, which interacted with the solar wind to dazzle observers with its varied structure. Such a special event occurred on 25 December 2021, when the gas tail was disconnected by the solar wind.

The Comet of Surprises reached its perihelion in January 2022 under much calmer conditions. Despite a few small outbursts, it faded at a relatively steady pace. The structure of tail changed significantly in the first days of 2022: gas tail narrowed, making dust tail separable and dominant. Like most known comets, the comet Leonard, only 1 km in diameter, originated in the Oort cloud. Comets coming from there can have an orbital period of tens of thousands of years around the Sun. Comet C/2021 A1 (Leonard) last visited the inner Solar System 80,000 years ago, but is likely to leave the Solar System after this perihelion.

"This comet belongs to no one person, it is for all of us to marvel at, and to enjoy the light it casts into our eyes, into our camera sensors, and our hearts." – said discoverer Gregory Leonard. We are all lucky indeed that in the year 2021 we are not without an awe-inspiring comet. The dirty snowball came, saw, won, and became the comet of the year, even if it only showed us its true, textbook breathtaking face by remote control!