C/2021 C1 (Rankin)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	5 Dec 2020	20.0	3.473 AU	4.189 AU	13h59m	-24°40'	38.5°	10.2°	276°
Nearest approach	23 Mar 2021	19.2	3.613 AU	2.621 AU	12h33m	-04°42'	173.6°	1.8°	302°
Today	24 Oct 2025	28.4	13.536 AU	13.165 AU	06h32m	+61°17'	109.9°	4.0°	258°

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. (11.5 + 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 C1 (Rankin) are:

    e (Eccentricity)                : 0.9979120
    q (Perihelion distance)         : 3.4730460
    i (Inclination)                 : 143.04390
    Ω (Longitude of ascending node) : 186.80960
    ω (Argument of perihelion)      : 336.03720
    L (Longitude of perihelion)     : 206.36256
    B (Latitude of perihelion)      : -14.13306
    T (Time of perihelion passage)  : 2459188.94420
    P (Orbital period in years)     : 67837.54

    Epoch                           : 2025 Oct 23
    Reference                       : MPEC 2023-KD6

    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
2025-10-23 00:00 UT   06 33 05.9   +61 14 28    13.172   13.530  109.0    4.0   259   28.4 
2025-10-24 00:00 UT   06 32 43.0   +61 17 08    13.165   13.535  109.8    4.0   258   28.4 
2025-10-24 00:47 UT   06 32 42.2   +61 17 13    13.165   13.536  109.9    4.0   258   28.4 
2025-10-25 00:00 UT   06 32 19.4   +61 19 46    13.158   13.541  110.6    3.9   257   28.4 
2025-10-26 00:00 UT   06 31 55.1   +61 22 24    13.152   13.547  111.4    3.9   256   28.4 
2025-10-27 00:00 UT   06 31 30.0   +61 25 00    13.145   13.553  112.2    3.9   255   28.4 
2025-10-28 00:00 UT   06 31 04.4   +61 27 35    13.139   13.558  113.0    3.9   254   28.4 
2025-10-29 00:00 UT   06 30 38.0   +61 30 09    13.133   13.564  113.8    3.8   254   28.4 
2025-10-30 00:00 UT   06 30 11.0   +61 32 41    13.127   13.570  114.5    3.8   253   28.4 
2025-10-31 00:00 UT   06 29 43.3   +61 35 12    13.121   13.575  115.3    3.8   252   28.4 
2025-11-01 00:00 UT   06 29 14.9   +61 37 42    13.115   13.581  116.1    3.8   251   28.4 
2025-11-02 00:00 UT   06 28 45.8   +61 40 09    13.110   13.587  116.8    3.7   250   28.4 
2025-11-03 00:00 UT   06 28 16.2   +61 42 35    13.104   13.592  117.6    3.7   249   28.4 

    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.