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C/2021 A1 (Leonard) - DISINTEGRATED
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach13 Dec 20212.90.774 AU0.233 AU 17h13m-00°47'22.4°151.0°356°
Perihelion3 Jan 20225.90.615 AU0.924 AU 21h40m-35°23'37.4°76.5°98°
Disintegration1 Mar 202211.01.279 AU1.991 AU 21h24m-34°51'32.9°24.9°219°
Today7 Nov 2025-13.210 AU14.129 AU 16h05m-06°52'21.1°1.5°62°
C/2021 A1 (Leonard)- 2025-11-07
astro.vanbuitenen.nl


 
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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)                : 1.0002680
    q (Perihelion distance)         : 0.6148200
    i (Inclination)                 : 132.74470
    Ω (Longitude of ascending node) : 255.90670
    ω (Argument of perihelion)      : 225.12520
    L (Longitude of perihelion)     : 221.62423
    B (Latitude of perihelion)      : -31.36058
    T (Time of perihelion passage)  : 2459583.49400

    Epoch                           : 2025 Nov 06
    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
2025-11-06 00:00 UT   16 05 09.5   -06 51 42    14.118   13.203   21.8    1.6    64   26.4 
2025-11-07 00:00 UT   16 05 24.7   -06 52 27    14.129   13.210   21.1    1.5    62   26.5 
2025-11-07 00:46 UT   16 05 25.2   -06 52 28    14.129   13.210   21.1    1.5    62   26.5 
2025-11-08 00:00 UT   16 05 39.9   -06 53 11    14.140   13.216   20.4    1.5    60   26.5 
2025-11-09 00:00 UT   16 05 55.3   -06 53 55    14.151   13.223   19.7    1.4    58   26.5 
2025-11-10 00:00 UT   16 06 10.7   -06 54 37    14.161   13.229   19.1    1.4    56   26.5 
2025-11-11 00:00 UT   16 06 26.1   -06 55 19    14.171   13.236   18.4    1.4    54   26.5 
2025-11-12 00:00 UT   16 06 41.7   -06 55 60    14.181   13.242   17.8    1.3    52   26.5 
2025-11-13 00:00 UT   16 06 57.2   -06 56 40    14.190   13.249   17.2    1.3    49   26.5 
2025-11-14 00:00 UT   16 07 12.9   -06 57 19    14.200   13.255   16.7    1.2    47   26.5 
2025-11-15 00:00 UT   16 07 28.5   -06 57 57    14.209   13.262   16.2    1.2    44   26.5 
2025-11-16 00:00 UT   16 07 44.2   -06 58 34    14.217   13.269   15.7    1.2    41   26.5 
2025-11-17 00:00 UT   16 07 60.0   -06 59 10    14.226   13.275   15.3    1.1    38   26.5 




    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.

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