C/2021 A1 (Leonard) - DISINTEGRATED
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	13 Dec 2021	2.9	0.774 AU	0.233 AU	17h12m	-00°50'	22.4°	151.1°	355°
Perihelion	3 Jan 2022	5.9	0.615 AU	0.924 AU	21h40m	-35°24'	37.5°	76.5°	98°
Disintegration	1 Mar 2022	11.0	1.279 AU	1.992 AU	21h24m	-34°51'	32.9°	24.9°	220°
Today	17 Oct 2025	-	13.073 AU	13.845 AU	16h00m	-06°34'	37.9°	2.7°	83°

The interactive orbit chart above shows the comet's path through the solar system and its position at the given date. Green and blue lines are shown perpendicular to the ecliptic plane: Green if the path is above the ecliptic plane, blue if it is below. (Left-click and drag to rotate the view; Right-click and drag to move the view; Use scroll wheel to zoom in our out.)

Light curve

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations from COBS. This lightcurve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 8.4 + 5 log[∆] + 11.0 log[r]). An additional green curve is displayed when an increase in apparent brightness is expected due to forward scattering of sunlight, which occurs when a dust-rich comet is located between the Earth and the Sun. (See Marcus 2007)

Charts

The all-sky chart below shows the path of the comet over the same period as the light curve. The comet's current position is marked yellow.

The following chart shows the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Orbital elements

The orbital elements of C/2021 A1 (Leonard) are:

    e (Eccentricity)                : 1.0002650
    q (Perihelion distance)         : 0.6149360
    i (Inclination)                 : 132.74740
    Ω (Longitude of ascending node) : 255.90800
    ω (Argument of perihelion)      : 225.12810
    L (Longitude of perihelion)     : 221.62147
    B (Latitude of perihelion)      : -31.36082
    T (Time of perihelion passage)  : 2459583.46180

    Epoch                           : 2025 Oct 15
    Reference                       : MPEC 2025-A40

    Classification(s):              : Nearly isotropic; New (a > 10000 AU)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-10-16 00:00 UT   16 00 13.4   -06 33 09    13.825   13.065   38.9    2.7    84   26.4 
2025-10-17 00:00 UT   16 00 26.2   -06 34 08    13.842   13.072   38.1    2.7    84   26.4 
2025-10-17 04:24 UT   16 00 28.6   -06 34 19    13.845   13.073   37.9    2.7    83   26.4 
2025-10-18 00:00 UT   16 00 39.2   -06 35 06    13.858   13.078   37.2    2.6    83   26.4 
2025-10-19 00:00 UT   16 00 52.3   -06 36 04    13.874   13.085   36.3    2.6    82   26.4 
2025-10-20 00:00 UT   16 01 05.6   -06 37 02    13.889   13.092   35.5    2.5    82   26.4 
2025-10-21 00:00 UT   16 01 19.0   -06 37 58    13.905   13.098   34.6    2.5    81   26.4 
2025-10-22 00:00 UT   16 01 32.5   -06 38 55    13.920   13.105   33.8    2.4    80   26.4 
2025-10-23 00:00 UT   16 01 46.2   -06 39 51    13.935   13.111   32.9    2.4    80   26.4 
2025-10-24 00:00 UT   16 01 60.0   -06 40 46    13.950   13.118   32.1    2.3    79   26.4 
2025-10-25 00:00 UT   16 02 13.9   -06 41 40    13.964   13.124   31.2    2.3    78   26.4 
2025-10-26 00:00 UT   16 02 28.0   -06 42 34    13.978   13.131   30.4    2.2    77   26.4 
2025-10-27 00:00 UT   16 02 42.1   -06 43 28    13.992   13.138   29.6    2.1    76   26.4 

    Terminology:
            
    delta:  distance between comet and earth in AU
    radius: distance between comet and sun in AU
    magn:   magnitude (brightness) estimate    
    ra:     right ascension in hours (24h = 360deg)
    dec:    declination in degrees
    elong:  elongation in degrees (angle sun-earth-comet)    
    phase:  phase angle in degrees (angle sun-comet-earth)        
    AU:     Astronomical Unit (mean distance between earth and sun: 149597870.7 km      
    

Orbital elements usually provided by the MPC (Minor Planet Center).
Observations contributed by observers worldwide, via COBS (Comet Observation Database) or the MPC (Minor Planet Center)
Calculations by a modified version of AAPlus, a C# implementation of the AA+ project by PJ Naughter from the algorithms presented in the book "Astronomical Algorithms" by Jean Meeus.
NGC2000 dso catalog and star labels from VizieR as provided by the Strasbourg astronomical Data Center.
Tycho2 catalog from the ESO archive.