C/2021 K2 (MASTER)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	13 Jul 2021	18.7	5.477 AU	4.558 AU	19h28m	-49°43'	152.1°	5.0°	1°
Perihelion	9 Sep 2021	18.9	5.461 AU	5.067 AU	18h25m	-41°05'	107.9°	10.1°	81°
Today	14 Dec 2025	24.1	11.747 AU	12.050 AU	17h12m	+46°31'	69.8°	4.5°	357°

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. (8.0 + 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 K2 (MASTER) are:

    e (Eccentricity)                : 1.0001950
    q (Perihelion distance)         : 5.4608920
    i (Inclination)                 : 100.87200
    Ω (Longitude of ascending node) : 282.34040
    ω (Argument of perihelion)      : 343.24160
    L (Longitude of perihelion)     : 285.59114
    B (Latitude of perihelion)      : -16.44897
    T (Time of perihelion passage)  : 2459466.53270

    Epoch                           : 2025 Dec 13
    Reference                       : MPEC 2022-O01

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-13 00:00 UT   17 12 21.3   +46 29 53    12.046   11.740   69.6    4.5   358   24.1 
2025-12-14 00:00 UT   17 12 46.9   +46 31 20    12.049   11.745   69.8    4.5   357   24.1 
2025-12-14 08:41 UT   17 12 56.2   +46 31 52    12.050   11.747   69.8    4.5   357   24.1 
2025-12-15 00:00 UT   17 13 12.5   +46 32 51    12.052   11.750   69.9    4.5   356   24.1 
2025-12-16 00:00 UT   17 13 38.0   +46 34 27    12.055   11.756   70.0    4.5   355   24.1 
2025-12-17 00:00 UT   17 14 03.6   +46 36 07    12.058   11.761   70.1    4.5   354   24.1 
2025-12-18 00:00 UT   17 14 29.0   +46 37 52    12.061   11.766   70.3    4.5   353   24.1 
2025-12-19 00:00 UT   17 14 54.5   +46 39 41    12.064   11.771   70.4    4.5   352   24.1 
2025-12-20 00:00 UT   17 15 19.9   +46 41 35    12.066   11.776   70.6    4.5   351   24.1 
2025-12-21 00:00 UT   17 15 45.2   +46 43 33    12.069   11.781   70.7    4.5   350   24.1 
2025-12-22 00:00 UT   17 16 10.5   +46 45 36    12.072   11.787   70.9    4.5   349   24.1 
2025-12-23 00:00 UT   17 16 35.8   +46 47 43    12.074   11.792   71.1    4.5   348   24.1 
2025-12-24 00:00 UT   17 17 00.9   +46 49 54    12.076   11.797   71.2    4.5   347   24.1 

    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.