C/2021 C3 (Catalina)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	10 Feb 2021	18.7	2.275 AU	1.668 AU	13h33m	-13°29'	115.5°	23.0°	293°
Nearest approach	13 Mar 2021	18.2	2.300 AU	1.327 AU	12h22m	+12°11'	164.6°	6.6°	234°
Today	17 Oct 2025	30.8	13.374 AU	12.635 AU	00h42m	+51°58'	136.3°	2.9°	163°

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. (14.0 + 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 C3 (Catalina) are:

    e (Eccentricity)                : 0.9623010
    q (Perihelion distance)         : 2.2747970
    i (Inclination)                 : 122.22030
    Ω (Longitude of ascending node) : 181.83510
    ω (Argument of perihelion)      : 356.97000
    L (Longitude of perihelion)     : 183.45170
    B (Latitude of perihelion)      : -2.56305
    T (Time of perihelion passage)  : 2459256.41480
    P (Orbital period in years)     : 468.73

    Epoch                           : 2025 Oct 16
    Reference                       : MPEC 2024-M41

    Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); External (P > 200 years)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-10-16 00:00 UT   00 43 00.8   +52 04 07    12.629   13.364  135.9    3.0   166   30.8 
2025-10-17 00:00 UT   00 42 32.4   +52 01 22    12.632   13.369  136.2    3.0   164   30.8 
2025-10-17 20:17 UT   00 42 08.5   +51 58 60    12.635   13.374  136.3    2.9   163   30.8 
2025-10-18 00:00 UT   00 42 04.2   +51 58 33    12.635   13.375  136.4    2.9   162   30.8 
2025-10-19 00:00 UT   00 41 36.2   +51 55 41    12.639   13.380  136.6    2.9   161   30.8 
2025-10-20 00:00 UT   00 41 08.3   +51 52 46    12.643   13.386  136.7    2.9   159   30.8 
2025-10-21 00:00 UT   00 40 40.7   +51 49 47    12.647   13.392  136.9    2.9   158   30.8 
2025-10-22 00:00 UT   00 40 13.3   +51 46 44    12.652   13.397  137.0    2.9   156   30.8 
2025-10-23 00:00 UT   00 39 46.1   +51 43 39    12.656   13.403  137.1    2.9   154   30.8 
2025-10-24 00:00 UT   00 39 19.1   +51 40 30    12.661   13.409  137.2    2.9   153   30.8 
2025-10-25 00:00 UT   00 38 52.4   +51 37 17    12.666   13.414  137.3    2.9   151   30.8 
2025-10-26 00:00 UT   00 38 26.0   +51 34 02    12.672   13.420  137.3    2.9   149   30.8 
2025-10-27 00:00 UT   00 37 59.8   +51 30 44    12.677   13.426  137.4    2.9   148   30.8 

    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.