C/2021 K2 (MASTER)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	13 Jul 2021	18.7	5.480 AU	4.561 AU	19h28m	-49°41'	152.1°	5.0°	1°
Perihelion	9 Sep 2021	18.9	5.464 AU	5.072 AU	18h25m	-41°03'	107.7°	10.1°	81°
Today	12 Jul 2025	23.5	10.940 AU	10.719 AU	17h03m	+51°54'	99.9°	5.3°	147°

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.)

The orbital elements of C/2021 K2 (MASTER) are:

            e (Eccentricity)                : 1.0004360
            q (Perihelion distance)         : 5.4635310
            i (Inclination)                 : 100.87130
            Ω (Longitude of ascending node) : 282.33800
            ω (Argument of perihelion)      : 343.27500
            L (Longitude of perihelion)     : 285.58168
            B (Latitude of perihelion)      : -16.41626
            T (Time of perihelion passage)  : 2459466.73150

            Epoch                           : 2025 Jul 11
            Reference                       : MPEC 2022-O01

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

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. 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. (8.00 + 5 log[∆] + 10.00 log[r]).

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-07-12 00:00 UT   17 03 58.4   +51 54 20    10.717   10.939   99.9    5.3   147   23.5 
2025-07-12 05:27 UT   17 03 50.8   +51 54 02    10.719   10.940   99.9    5.3   147   23.5 
2025-07-13 00:00 UT   17 03 25.0   +51 52 58    10.727   10.944   99.7    5.3   146   23.5 
2025-07-14 00:00 UT   17 02 52.1   +51 51 31    10.736   10.949   99.4    5.3   145   23.5 
2025-07-15 00:00 UT   17 02 19.5   +51 49 59    10.746   10.955   99.2    5.3   144   23.6 
2025-07-16 00:00 UT   17 01 47.4   +51 48 22    10.755   10.960   98.9    5.3   143   23.6 
2025-07-17 00:00 UT   17 01 15.7   +51 46 40    10.765   10.965   98.7    5.3   142   23.6 
2025-07-18 00:00 UT   17 00 44.5   +51 44 54    10.775   10.970   98.4    5.3   141   23.6 
2025-07-19 00:00 UT   17 00 13.8   +51 43 03    10.785   10.975   98.2    5.3   140   23.6 
2025-07-20 00:00 UT   16 59 43.5   +51 41 08    10.795   10.981   97.9    5.3   139   23.6 
2025-07-21 00:00 UT   16 59 13.7   +51 39 09    10.804   10.986   97.6    5.3   138   23.6 
2025-07-22 00:00 UT   16 58 44.4   +51 37 05    10.814   10.991   97.3    5.3   137   23.6 

    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.