C/2021 K2 (MASTER)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	13 Jul 2021	18.7	5.473 AU	4.554 AU	19h27m	-49°42'	152.1°	5.0°	1°
Perihelion	8 Sep 2021	18.9	5.457 AU	5.055 AU	18h25m	-41°09'	108.3°	10.1°	81°
Today	13 May 2026	24.4	12.528 AU	12.317 AU	17h16m	+58°10'	99.8°	4.6°	208°

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)                : 1.0000510
    q (Perihelion distance)         : 5.4565780
    i (Inclination)                 : 100.88550
    Ω (Longitude of ascending node) : 282.29220
    ω (Argument of perihelion)      : 343.21470
    L (Longitude of perihelion)     : 285.55244
    B (Latitude of perihelion)      : -16.47458
    T (Time of perihelion passage)  : 2459466.03290

    Epoch                           : 2026 May 13
    Reference                       : MPEC 2026-E44

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-05-12 00:00 UT   17 17 17.4   +58 04 11    12.308   12.519   99.8    4.6   210   24.4 
2026-05-13 00:00 UT   17 16 42.0   +58 07 37    12.313   12.524   99.8    4.6   209   24.4 
2026-05-13 18:35 UT   17 16 14.3   +58 10 12    12.317   12.528   99.8    4.6   208   24.4 
2026-05-14 00:00 UT   17 16 06.2   +58 10 57    12.318   12.530   99.8    4.6   207   24.4 
2026-05-15 00:00 UT   17 15 30.0   +58 14 13    12.323   12.535   99.8    4.6   206   24.4 
2026-05-16 00:00 UT   17 14 53.6   +58 17 23    12.329   12.540   99.7    4.6   205   24.4 
2026-05-17 00:00 UT   17 14 16.7   +58 20 28    12.334   12.545   99.7    4.6   204   24.4 
2026-05-18 00:00 UT   17 13 39.6   +58 23 28    12.340   12.550   99.7    4.6   203   24.4 
2026-05-19 00:00 UT   17 13 02.2   +58 26 23    12.345   12.555   99.7    4.6   202   24.4 
2026-05-20 00:00 UT   17 12 24.4   +58 29 13    12.351   12.561   99.6    4.6   201   24.4 
2026-05-21 00:00 UT   17 11 46.4   +58 31 57    12.357   12.566   99.6    4.6   200   24.5 
2026-05-22 00:00 UT   17 11 08.1   +58 34 35    12.363   12.571   99.5    4.6   198   24.5 
2026-05-23 00:00 UT   17 10 29.6   +58 37 09    12.369   12.576   99.5    4.6   197   24.5 

    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.