C/2021 K2 (MASTER)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	13 Jul 2021	18.7	5.476 AU	4.558 AU	19h28m	-49°43'	152.1°	5.0°	1°
Perihelion	8 Sep 2021	18.9	5.460 AU	5.065 AU	18h25m	-41°06'	108.0°	10.1°	81°
Today	4 Feb 2026	24.2	12.016 AU	12.123 AU	17h32m	+49°24'	81.4°	4.7°	308°

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)                : 1.0001170
    q (Perihelion distance)         : 5.4600540
    i (Inclination)                 : 100.87200
    Ω (Longitude of ascending node) : 282.34010
    ω (Argument of perihelion)      : 343.23100
    L (Longitude of perihelion)     : 285.59301
    B (Latitude of perihelion)      : -16.45936
    T (Time of perihelion passage)  : 2459466.46910

    Epoch                           : 2026 Feb 03
    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
2026-02-03 00:00 UT   17 31 45.9   +49 19 07    12.123   12.010   81.1    4.7   309   24.2 
2026-02-04 00:00 UT   17 32 01.9   +49 24 02    12.123   12.015   81.4    4.7   308   24.2 
2026-02-04 03:28 UT   17 32 04.2   +49 24 44    12.123   12.016   81.4    4.7   308   24.2 
2026-02-05 00:00 UT   17 32 17.6   +49 28 59    12.124   12.020   81.6    4.7   307   24.2 
2026-02-06 00:00 UT   17 32 32.8   +49 34 00    12.124   12.025   81.9    4.7   306   24.2 
2026-02-07 00:00 UT   17 32 47.8   +49 39 04    12.124   12.031   82.2    4.7   305   24.2 
2026-02-08 00:00 UT   17 33 02.3   +49 44 11    12.124   12.036   82.5    4.7   304   24.2 
2026-02-09 00:00 UT   17 33 16.5   +49 49 20    12.125   12.041   82.8    4.7   303   24.2 
2026-02-10 00:00 UT   17 33 30.2   +49 54 32    12.125   12.046   83.1    4.7   302   24.2 
2026-02-11 00:00 UT   17 33 43.6   +49 59 47    12.125   12.051   83.4    4.7   302   24.2 
2026-02-12 00:00 UT   17 33 56.6   +50 05 05    12.125   12.056   83.6    4.7   301   24.2 
2026-02-13 00:00 UT   17 34 09.1   +50 10 25    12.126   12.062   83.9    4.7   300   24.2 
2026-02-14 00:00 UT   17 34 21.2   +50 15 47    12.126   12.067   84.2    4.7   299   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.