C/2021 C1 (Rankin)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	4 Dec 2020	20.0	3.475 AU	4.197 AU	13h59m	-24°37'	38.1°	10.1°	275°
Nearest approach	23 Mar 2021	19.2	3.616 AU	2.624 AU	12h33m	-04°38'	173.6°	1.8°	302°
Today	15 Jul 2026	29.3	15.013 AU	15.759 AU	05h47m	+57°54'	41.5°	2.6°	319°

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)                : 0.9976570
    q (Perihelion distance)         : 3.4747960
    i (Inclination)                 : 143.04630
    Ω (Longitude of ascending node) : 186.77460
    ω (Argument of perihelion)      : 336.01280
    L (Longitude of perihelion)     : 206.34887
    B (Latitude of perihelion)      : -14.14608
    T (Time of perihelion passage)  : 2459188.37150
    P (Orbital period in years)     : 57113.07

    Epoch                           : 2026 May 29
    Reference                       : MPC194173

    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
2026-07-14 00:00 UT   05 47 21.3   +57 52 59    15.759   15.004   40.8    2.5   321   29.2 
2026-07-15 00:00 UT   05 47 41.4   +57 53 53    15.759   15.010   41.2    2.6   320   29.3 
2026-07-15 14:25 UT   05 47 53.3   +57 54 26    15.759   15.013   41.5    2.6   319   29.3 
2026-07-16 00:00 UT   05 48 01.3   +57 54 48    15.758   15.015   41.7    2.6   319   29.3 
2026-07-17 00:00 UT   05 48 21.0   +57 55 46    15.758   15.021   42.2    2.6   318   29.3 
2026-07-18 00:00 UT   05 48 40.4   +57 56 44    15.757   15.026   42.7    2.6   317   29.3 
2026-07-19 00:00 UT   05 48 59.7   +57 57 45    15.756   15.032   43.2    2.7   316   29.3 
2026-07-20 00:00 UT   05 49 18.8   +57 58 47    15.755   15.037   43.7    2.7   315   29.3 
2026-07-21 00:00 UT   05 49 37.7   +57 59 51    15.753   15.043   44.3    2.7   314   29.3 
2026-07-22 00:00 UT   05 49 56.4   +58 00 57    15.752   15.048   44.8    2.7   313   29.3 
2026-07-23 00:00 UT   05 50 14.8   +58 02 04    15.750   15.054   45.4    2.8   312   29.3 
2026-07-24 00:00 UT   05 50 33.0   +58 03 13    15.748   15.059   45.9    2.8   311   29.3 
2026-07-25 00:00 UT   05 50 51.0   +58 04 23    15.745   15.065   46.5    2.8   310   29.3 

    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.