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C/2021 K3 (Catalina)
ephemeris date magn radius delta ra dec elong phase PA
Perihelion3 Feb 202221.15.225 AU6.155 AU 19h55m-22°01'17.8°3.3°255°
Nearest approach28 Jun 202220.55.338 AU4.358 AU 19h01m-38°56'162.8°3.2°333°
Today18 Dec 202525.711.025 AU11.319 AU 11h59m-48°35'70.2°4.8°283°
C/2021 K3 (Catalina)- 2025-12-18
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. The light curve is based on the absolute magnitude and slope parameter as calculated from an MPEC, or the latest values provided by the minor planet center. (10.0 + 5 log[∆] + 10.0 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 K3 (Catalina) are: 

    e (Eccentricity)                : 1.0039030
    q (Perihelion distance)         : 5.2251860
    i (Inclination)                 : 134.78040
    Ω (Longitude of ascending node) : 114.61490
    ω (Argument of perihelion)      : 181.98320
    L (Longitude of perihelion)     : 113.21767
    B (Latitude of perihelion)      : -1.40756
    T (Time of perihelion passage)  : 2459613.91840

    Epoch                           : 2025 Dec 17
    Reference                       : MPEC 2022-L66

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-17 00:00 UT   11 59 29.3   -48 31 11    11.327   11.018   69.3    4.8   282   25.7 
2025-12-18 00:00 UT   11 59 22.9   -48 34 23    11.321   11.023   70.0    4.8   283   25.7 
2025-12-18 07:46 UT   11 59 20.8   -48 35 24    11.319   11.025   70.2    4.8   283   25.7 
2025-12-19 00:00 UT   11 59 16.0   -48 37 33    11.315   11.029   70.7    4.8   284   25.7 
2025-12-20 00:00 UT   11 59 08.6   -48 40 43    11.308   11.034   71.4    4.8   285   25.7 
2025-12-21 00:00 UT   11 59 00.6   -48 43 51    11.302   11.039   72.1    4.9   285   25.7 
2025-12-22 00:00 UT   11 58 52.1   -48 46 58    11.295   11.045   72.8    4.9   286   25.7 
2025-12-23 00:00 UT   11 58 43.0   -48 50 04    11.289   11.050   73.5    4.9   287   25.7 
2025-12-24 00:00 UT   11 58 33.4   -48 53 09    11.282   11.055   74.2    4.9   288   25.7 
2025-12-25 00:00 UT   11 58 23.2   -48 56 12    11.275   11.061   74.9    4.9   288   25.7 
2025-12-26 00:00 UT   11 58 12.5   -48 59 13    11.268   11.066   75.7    4.9   289   25.7 
2025-12-27 00:00 UT   11 58 01.2   -49 02 13    11.261   11.071   76.4    5.0   290   25.7 
2025-12-28 00:00 UT   11 57 49.3   -49 05 11    11.254   11.076   77.1    5.0   291   25.7 




    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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