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°42'	152.1°	5.0°	1°
Perihelion	9 Sep 2021	18.9	5.463 AU	5.072 AU	18h25m	-41°03'	107.7°	10.1°	81°
Today	8 Aug 2025	23.7	11.084 AU	11.001 AU	16h51m	+50°49'	92.0°	5.2°	119°

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)                : 1.0004020
            q (Perihelion distance)         : 5.4631500
            i (Inclination)                 : 100.87160
            Ω (Longitude of ascending node) : 282.33900
            ω (Argument of perihelion)      : 343.27020
            L (Longitude of perihelion)     : 285.58375
            B (Latitude of perihelion)      : -16.42095
            T (Time of perihelion passage)  : 2459466.70310

            Epoch                           : 2025 Aug 07
            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
2025-08-08 00:00 UT   16 51 47.6   +50 52 42    10.992   11.079   92.3    5.2   120   23.7 
2025-08-08 21:31 UT   16 51 30.1   +50 49 58    11.001   11.084   92.0    5.2   119   23.7 
2025-08-09 00:00 UT   16 51 28.1   +50 49 38    11.003   11.085   92.0    5.2   119   23.7 
2025-08-10 00:00 UT   16 51 09.2   +50 46 32    11.013   11.090   91.7    5.2   118   23.7 
2025-08-11 00:00 UT   16 50 50.9   +50 43 24    11.024   11.095   91.4    5.2   117   23.7 
2025-08-12 00:00 UT   16 50 33.2   +50 40 13    11.035   11.100   91.1    5.2   116   23.7 
2025-08-13 00:00 UT   16 50 16.0   +50 37 00    11.046   11.106   90.7    5.2   115   23.7 
2025-08-14 00:00 UT   16 49 59.4   +50 33 45    11.057   11.111   90.4    5.2   114   23.7 
2025-08-15 00:00 UT   16 49 43.4   +50 30 29    11.068   11.116   90.1    5.2   113   23.7 
2025-08-16 00:00 UT   16 49 28.0   +50 27 10    11.078   11.121   89.8    5.2   112   23.7 
2025-08-17 00:00 UT   16 49 13.2   +50 23 50    11.089   11.126   89.5    5.2   111   23.7 
2025-08-18 00:00 UT   16 48 58.9   +50 20 28    11.100   11.132   89.1    5.2   110   23.7 

    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.