C/2021 K1 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	1 May 2021	16.1	2.503 AU	2.911 AU	23h04m	-06°59'	56.6°	19.6°	247°
Nearest approach	13 Sep 2021	15.7	2.816 AU	1.893 AU	01h17m	-10°33'	151.1°	9.9°	281°
Today	13 Dec 2025	25.4	11.319 AU	10.436 AU	07h08m	+11°51'	152.5°	2.3°	298°

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)                : 0.8012170
    q (Perihelion distance)         : 2.5028370
    i (Inclination)                 : 16.26920
    Ω (Longitude of ascending node) : 140.92960
    ω (Argument of perihelion)      : 184.20210
    L (Longitude of perihelion)     : 144.96400
    B (Latitude of perihelion)      : -1.17625
    T (Time of perihelion passage)  : 2459336.19920
    P (Orbital period in years)     : 44.68

    Epoch                           : 2025 Dec 12
    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
2025-12-12 00:00 UT   07 09 14.0   +11 50 60    10.442   11.312  150.8    2.4   296   25.4 
2025-12-13 00:00 UT   07 08 57.0   +11 51 18    10.438   11.316  151.8    2.4   297   25.4 
2025-12-13 17:39 UT   07 08 44.4   +11 51 32    10.436   11.319  152.5    2.3   298   25.4 
2025-12-14 00:00 UT   07 08 39.8   +11 51 37    10.435   11.320  152.8    2.3   298   25.4 
2025-12-15 00:00 UT   07 08 22.4   +11 51 57    10.433   11.324  153.8    2.2   299   25.4 
2025-12-16 00:00 UT   07 08 04.9   +11 52 19    10.430   11.329  154.8    2.1   300   25.4 
2025-12-17 00:00 UT   07 07 47.2   +11 52 42    10.428   11.333  155.8    2.0   301   25.4 
2025-12-18 00:00 UT   07 07 29.3   +11 53 06    10.426   11.337  156.7    2.0   302   25.4 
2025-12-19 00:00 UT   07 07 11.3   +11 53 32    10.425   11.342  157.7    1.9   304   25.4 
2025-12-20 00:00 UT   07 06 53.1   +11 53 59    10.424   11.346  158.6    1.8   305   25.4 
2025-12-21 00:00 UT   07 06 34.8   +11 54 27    10.423   11.350  159.6    1.7   307   25.4 
2025-12-22 00:00 UT   07 06 16.4   +11 54 56    10.422   11.354  160.5    1.7   308   25.4 
2025-12-23 00:00 UT   07 05 57.9   +11 55 26    10.422   11.359  161.4    1.6   310   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.