C/2021 K2 (MASTER)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	13 Jul 2021	18.7	5.479 AU	4.560 AU	19h28m	-49°42'	152.1°	5.0°	1°
Perihelion	9 Sep 2021	18.9	5.463 AU	5.071 AU	18h25m	-41°03'	107.8°	10.1°	81°
Today	31 Aug 2025	23.7	11.201 AU	11.247 AU	16h46m	+49°33'	84.8°	5.1°	97°

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)                : 1.0003700
            q (Perihelion distance)         : 5.4627830
            i (Inclination)                 : 100.87190
            Ω (Longitude of ascending node) : 282.33980
            ω (Argument of perihelion)      : 343.26560
            L (Longitude of perihelion)     : 285.58559
            B (Latitude of perihelion)      : -16.42545
            T (Time of perihelion passage)  : 2459466.67670

            Epoch                           : 2025 Aug 29
            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
2025-08-31 00:00 UT   16 46 47.1   +49 34 56    11.242   11.199   85.0    5.2    98   23.7 
2025-08-31 09:28 UT   16 46 44.6   +49 33 31    11.247   11.201   84.8    5.1    97   23.7 
2025-09-01 00:00 UT   16 46 41.0   +49 31 21    11.253   11.204   84.6    5.1    97   23.8 
2025-09-02 00:00 UT   16 46 35.5   +49 27 46    11.264   11.210   84.3    5.1    96   23.8 
2025-09-03 00:00 UT   16 46 30.5   +49 24 11    11.275   11.215   84.0    5.1    95   23.8 
2025-09-04 00:00 UT   16 46 26.1   +49 20 36    11.286   11.220   83.7    5.1    94   23.8 
2025-09-05 00:00 UT   16 46 22.3   +49 17 01    11.297   11.225   83.4    5.1    93   23.8 
2025-09-06 00:00 UT   16 46 19.0   +49 13 26    11.307   11.230   83.1    5.1    92   23.8 
2025-09-07 00:00 UT   16 46 16.2   +49 09 51    11.318   11.236   82.7    5.1    91   23.8 
2025-09-08 00:00 UT   16 46 14.0   +49 06 17    11.329   11.241   82.4    5.1    90   23.8 
2025-09-09 00:00 UT   16 46 12.3   +49 02 43    11.339   11.246   82.1    5.1    89   23.8 
2025-09-10 00:00 UT   16 46 11.2   +48 59 10    11.350   11.251   81.8    5.1    88   23.8 

    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.