Lens : Nikon AF/ED 80-200 mm F2.8 @ 80 mm 25% Cropped
ISO : 2500
Exposure : 180 Sec
WB : 3000
Tracking : SW Pro 2i
Location : Mae Pha Hean reservior, Sankampeang, CM
D/M/Y : 7 Dec 2021
Leonard C/2021 A1
On 12 December 2021 the comet will be 0.233 AU (34.9 million km) from Earth and on 18 December 2021 will be 0.028 AU (4.2 million km) from Venus. It will make its closest approach to the Sun on 3 January 2022. It reached naked eye visibility in December 2021. At an apparent magnitude of 4, it should be a good binocular comet. On 10 October the comet showed a short but dense dust tail. As of early December the comet has a total magnitude (coma+nucleus) of around 6. The first reports of naked eye observations started coming in on 5 December 2021.
On the morning of 6 December 2021 the comet will be about 5 degrees from the star Arcturus. On 14 December 2021 the comet will be 14.7 degrees from the Sun and will quickly become better seen from the southern hemisphere. The forward scattering of light could cause the comet to brighten to as much as magnitude ~2.
C/2021 A1 has been inside of the orbit of Neptune since May 2009. Using an epoch of 1950 which is well before the comet entered the planetary region of the Solar System, a barycentric orbit solution suggests the comet had roughly a 80 thousand year orbital period. Therefore the comet had spent the last 40 thousand years inbound from approximately 3,700 AU (550 billion km). After perihelion the comet will be ejected from the Solar System. The barycentric orbit will remain hyperbolic after September 2022.
Current system
Increasing numbers of comet discoveries made this procedure awkward, as did the delay between discovery and perihelion passage before the permanent name could be assigned. As a result, in 1994 the International Astronomical Union approved a new naming system. Comets are now provisionally designated by the year of their discovery followed by a letter indicating the half-month of the discovery and a number indicating the order of discovery (a system similar to that already used for asteroids). For example, the fourth comet discovered in the second half of February 2006 was designated 2006 D4. Prefixes are then added to indicate the nature of the comet:
P/ indicates a periodic comet, defined for these purposes as any comet with an orbital period of less than 200 years or confirmed observations at more than one perihelion passage.
C/ indicates a non-periodic comet i.e. any comet that is not periodic according to the preceding definition.
X/ indicates a comet for which no reliable orbit could be calculated (generally, historical comets).
D/ indicates a periodic comet that has disappeared, broken up, or been lost. Examples include Lexell's Comet (D/1770 L1) and Comet Shoemaker–Levy 9 (D/1993 F2)
A/ indicates an object that was mistakenly identified as a comet, but is actually a minor planet. An unused option for many years, this classification was first applied in 2017 for 'Oumuamua (A/2017 U1) and subsequently to all asteroids on comet-like orbits.
I/ indicates an interstellar object,[6] added to the system 2017 to allow the reclassification of 'Oumuamua (1I/2017 U1). As of 2019, the only other object with this classification is Comet Borisov (2I/2019 Q4).
For example, Comet Hale–Bopp's designation is C/1995 O1. After their second observed perihelion passage, designations of periodic comets are given an additional prefix number, indicating the order of their discovery. Halley's Comet, the first comet identified as periodic, has the systematic designation 1P/1682 Q1.