C/2021 K1 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	1 May 2021	16.1	2.503 AU	2.910 AU	23h04m	-06°59'	56.7°	19.7°	247°
Nearest approach	13 Sep 2021	15.7	2.816 AU	1.893 AU	01h17m	-10°33'	151.1°	9.9°	281°
Today	27 Nov 2025	25.4	11.248 AU	10.522 AU	07h13m	+11°49'	135.6°	3.5°	288°

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. This lightcurve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 9.8 + 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 K1 (ATLAS) are:

    e (Eccentricity)                : 0.8012400
    q (Perihelion distance)         : 2.5028150
    i (Inclination)                 : 16.26930
    Ω (Longitude of ascending node) : 140.92920
    ω (Argument of perihelion)      : 184.20450
    L (Longitude of perihelion)     : 144.96590
    B (Latitude of perihelion)      : -1.17693
    T (Time of perihelion passage)  : 2459336.26050
    P (Orbital period in years)     : 44.68

    Epoch                           : 2025 Nov 26
    Reference                       : MPEC 2022-O08

    Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); Halley type (P < 200 years)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-11-26 00:00 UT   07 13 15.6   +11 49 03    10.529   11.243  134.4    3.6   288   25.4 
2025-11-27 00:00 UT   07 13 02.5   +11 49 01    10.522   11.247  135.5    3.5   288   25.4 
2025-11-27 02:03 UT   07 13 01.4   +11 49 00    10.522   11.248  135.6    3.5   288   25.4 
2025-11-28 00:00 UT   07 12 49.0   +11 48 60    10.515   11.251  136.5    3.5   288   25.4 
2025-11-29 00:00 UT   07 12 35.3   +11 49 00    10.508   11.256  137.5    3.4   289   25.4 
2025-11-30 00:00 UT   07 12 21.3   +11 49 02    10.502   11.260  138.5    3.3   289   25.4 
2025-12-01 00:00 UT   07 12 07.0   +11 49 05    10.495   11.264  139.6    3.3   290   25.4 
2025-12-02 00:00 UT   07 11 52.5   +11 49 09    10.489   11.269  140.6    3.2   290   25.4 
2025-12-03 00:00 UT   07 11 37.7   +11 49 14    10.483   11.273  141.6    3.1   291   25.4 
2025-12-04 00:00 UT   07 11 22.7   +11 49 21    10.478   11.277  142.7    3.0   291   25.4 
2025-12-05 00:00 UT   07 11 07.4   +11 49 29    10.472   11.282  143.7    3.0   292   25.4 
2025-12-06 00:00 UT   07 10 51.9   +11 49 38    10.467   11.286  144.7    2.9   292   25.4 
2025-12-07 00:00 UT   07 10 36.1   +11 49 48    10.462   11.290  145.7    2.8   293   25.4 

    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.