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	5.073 AU	18h25m	-41°02'	107.7°	10.1°	81°
Today	28 Jun 2025	23.5	10.869 AU	10.598 AU	17h12m	+52°04'	102.8°	5.2°	162°

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)                : 1.0004530
            q (Perihelion distance)         : 5.4637090
            i (Inclination)                 : 100.87120
            Ω (Longitude of ascending node) : 282.33750
            ω (Argument of perihelion)      : 343.27720
            L (Longitude of perihelion)     : 285.58070
            B (Latitude of perihelion)      : -16.41411
            T (Time of perihelion passage)  : 2459466.74530

            Epoch                           : 2025 Jun 27
            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
2025-06-28 00:00 UT   17 12 23.8   +52 04 14    10.594   10.866  102.9    5.2   162   23.5 
2025-06-28 13:00 UT   17 12 03.1   +52 04 12    10.598   10.869  102.8    5.2   162   23.5 
2025-06-29 00:00 UT   17 11 45.7   +52 04 08    10.602   10.871  102.7    5.2   161   23.5 
2025-06-30 00:00 UT   17 11 07.9   +52 03 56    10.610   10.876  102.5    5.2   160   23.5 
2025-07-01 00:00 UT   17 10 30.3   +52 03 39    10.619   10.882  102.3    5.2   159   23.5 
2025-07-02 00:00 UT   17 09 53.0   +52 03 16    10.627   10.887  102.1    5.2   158   23.5 
2025-07-03 00:00 UT   17 09 16.0   +52 02 47    10.636   10.892  101.9    5.2   157   23.5 
2025-07-04 00:00 UT   17 08 39.3   +52 02 12    10.645   10.897  101.7    5.2   156   23.5 
2025-07-05 00:00 UT   17 08 03.0   +52 01 32    10.653   10.903  101.5    5.2   155   23.5 
2025-07-06 00:00 UT   17 07 27.0   +52 00 46    10.662   10.908  101.3    5.2   154   23.5 
2025-07-07 00:00 UT   17 06 51.3   +51 59 55    10.671   10.913  101.1    5.2   153   23.5 
2025-07-08 00:00 UT   17 06 16.0   +51 58 58    10.680   10.918  100.9    5.2   151   23.5 

    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.