C/2021 K1 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	1 May 2021	16.1	2.503 AU	2.908 AU	23h05m	-06°58'	56.8°	19.7°	247°
Nearest approach	13 Sep 2021	15.7	2.815 AU	1.891 AU	01h17m	-10°34'	151.2°	9.9°	281°
Today	14 Oct 2025	25.4	11.059 AU	10.979 AU	07h17m	+12°07'	92.0°	5.2°	278°

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)                : 0.8013070
    q (Perihelion distance)         : 2.5027080
    i (Inclination)                 : 16.26980
    Ω (Longitude of ascending node) : 140.92780
    ω (Argument of perihelion)      : 184.21100
    L (Longitude of perihelion)     : 144.97073
    B (Latitude of perihelion)      : -1.17878
    T (Time of perihelion passage)  : 2459336.43480
    P (Orbital period in years)     : 44.70

    Epoch                           : 2025 Oct 13
    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
2025-10-14 00:00 UT   07 17 17.7   +12 08 13    10.987   11.056   91.3    5.2   278   25.4 
2025-10-14 16:19 UT   07 17 19.1   +12 07 41    10.979   11.059   92.0    5.2   278   25.4 
2025-10-15 00:00 UT   07 17 19.8   +12 07 27    10.975   11.060   92.3    5.2   278   25.4 
2025-10-16 00:00 UT   07 17 21.5   +12 06 41    10.963   11.065   93.3    5.2   278   25.4 
2025-10-17 00:00 UT   07 17 22.9   +12 05 57    10.950   11.069   94.2    5.2   278   25.4 
2025-10-18 00:00 UT   07 17 23.9   +12 05 13    10.938   11.074   95.2    5.1   279   25.4 
2025-10-19 00:00 UT   07 17 24.5   +12 04 29    10.926   11.078   96.2    5.1   279   25.4 
2025-10-20 00:00 UT   07 17 24.7   +12 03 47    10.914   11.082   97.2    5.1   279   25.4 
2025-10-21 00:00 UT   07 17 24.6   +12 03 05    10.901   11.087   98.1    5.1   279   25.4 
2025-10-22 00:00 UT   07 17 24.1   +12 02 25    10.889   11.091   99.1    5.1   279   25.4 
2025-10-23 00:00 UT   07 17 23.2   +12 01 45    10.877   11.095  100.1    5.1   280   25.4 
2025-10-24 00:00 UT   07 17 21.9   +12 01 05    10.865   11.100  101.1    5.0   280   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.