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	8 Sep 2021	18.9	5.460 AU	5.066 AU	18h25m	-41°06'	107.9°	10.1°	81°
Today	12 Jan 2026	24.2	11.898 AU	12.109 AU	17h24m	+47°46'	75.3°	4.6°	329°

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)                : 1.0001510
    q (Perihelion distance)         : 5.4604260
    i (Inclination)                 : 100.87200
    Ω (Longitude of ascending node) : 282.34020
    ω (Argument of perihelion)      : 343.23560
    L (Longitude of perihelion)     : 285.59217
    B (Latitude of perihelion)      : -16.45485
    T (Time of perihelion passage)  : 2459466.49660

    Epoch                           : 2026 Jan 11
    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
2026-01-11 00:00 UT   17 24 13.2   +47 41 44    12.107   11.890   75.0    4.6   330   24.2 
2026-01-12 00:00 UT   17 24 35.7   +47 45 16    12.109   11.896   75.2    4.6   329   24.2 
2026-01-12 09:53 UT   17 24 44.9   +47 46 45    12.109   11.898   75.3    4.6   329   24.2 
2026-01-13 00:00 UT   17 24 57.9   +47 48 53    12.110   11.901   75.4    4.6   328   24.2 
2026-01-14 00:00 UT   17 25 20.0   +47 52 34    12.111   11.906   75.7    4.6   328   24.2 
2026-01-15 00:00 UT   17 25 41.9   +47 56 18    12.112   11.911   75.9    4.6   327   24.2 
2026-01-16 00:00 UT   17 26 03.5   +48 00 07    12.113   11.916   76.2    4.6   326   24.2 
2026-01-17 00:00 UT   17 26 24.9   +48 03 59    12.114   11.922   76.4    4.6   325   24.2 
2026-01-18 00:00 UT   17 26 46.0   +48 07 56    12.114   11.927   76.7    4.6   324   24.2 
2026-01-19 00:00 UT   17 27 06.9   +48 11 56    12.115   11.932   77.0    4.6   323   24.2 
2026-01-20 00:00 UT   17 27 27.6   +48 15 60    12.116   11.937   77.2    4.6   322   24.2 
2026-01-21 00:00 UT   17 27 47.9   +48 20 07    12.117   11.942   77.5    4.6   321   24.2 
2026-01-22 00:00 UT   17 28 08.0   +48 24 19    12.117   11.948   77.7    4.6   320   24.2 

    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.