C/2021 K1 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	1 May 2021	16.1	2.503 AU	2.920 AU	23h04m	-07°02'	56.1°	19.5°	247°
Nearest approach	13 Sep 2021	15.7	2.820 AU	1.897 AU	01h18m	-10°31'	151.1°	9.9°	281°
Today	13 Sep 2026	26.3	12.444 AU	12.943 AU	07h33m	+13°09'	58.3°	3.9°	274°

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)                : 0.8009980
    q (Perihelion distance)         : 2.5030570
    i (Inclination)                 : 16.26720
    Ω (Longitude of ascending node) : 140.93480
    ω (Argument of perihelion)      : 184.17710
    L (Longitude of perihelion)     : 144.94523
    B (Latitude of perihelion)      : -1.16912
    T (Time of perihelion passage)  : 2459335.55110
    P (Orbital period in years)     : 44.61

    Epoch                           : 2026 May 29
    Reference                       : MPC194174

    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
2026-09-12 00:00 UT   07 32 46.9   +13 11 11    12.963   12.436   56.5    3.9   273   26.3 
2026-09-13 00:00 UT   07 32 59.3   +13 10 19    12.953   12.440   57.4    3.9   274   26.3 
2026-09-13 23:22 UT   07 33 11.2   +13 09 28    12.943   12.444   58.3    3.9   274   26.3 
2026-09-14 00:00 UT   07 33 11.5   +13 09 27    12.943   12.444   58.3    3.9   274   26.3 
2026-09-15 00:00 UT   07 33 23.4   +13 08 35    12.932   12.448   59.2    4.0   274   26.3 
2026-09-16 00:00 UT   07 33 35.1   +13 07 44    12.922   12.452   60.1    4.0   274   26.3 
2026-09-17 00:00 UT   07 33 46.5   +13 06 53    12.911   12.456   61.1    4.0   274   26.3 
2026-09-18 00:00 UT   07 33 57.6   +13 06 02    12.900   12.460   62.0    4.1   275   26.3 
2026-09-19 00:00 UT   07 34 08.5   +13 05 11    12.889   12.464   62.9    4.1   275   26.3 
2026-09-20 00:00 UT   07 34 19.1   +13 04 20    12.878   12.468   63.8    4.1   275   26.3 
2026-09-21 00:00 UT   07 34 29.4   +13 03 30    12.867   12.472   64.7    4.2   275   26.3 
2026-09-22 00:00 UT   07 34 39.5   +13 02 40    12.856   12.475   65.6    4.2   275   26.3 
2026-09-23 00:00 UT   07 34 49.3   +13 01 50    12.844   12.479   66.6    4.2   276   26.3 

    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.