C/2021 S1 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	30 Dec 2021	18.5	6.143 AU	5.303 AU	06h23m	+56°59'	146.1°	5.1°	175°
Perihelion	2 Mar 2022	18.7	6.128 AU	5.777 AU	05h56m	+49°28'	106.2°	8.9°	98°
Today	8 Jan 2026	22.5	11.020 AU	10.558 AU	09h51m	-30°24'	115.7°	4.6°	320°

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. 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. (7.0 + 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 S1 (ATLAS) are:

    e (Eccentricity)                : 1.0029610
    q (Perihelion distance)         : 6.1280890
    i (Inclination)                 : 52.03400
    Ω (Longitude of ascending node) : 299.85030
    ω (Argument of perihelion)      : 148.34660
    L (Longitude of perihelion)     : 279.08054
    B (Latitude of perihelion)      : 24.43896
    T (Time of perihelion passage)  : 2459640.65040

    Epoch                           : 2026 Jan 07
    Reference                       : MPEC 2023-J29

    Classification(s):              : Nearly isotropic; New (a > 10000 AU)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-01-07 00:00 UT   09 51 51.3   -30 20 15    10.567   11.012  114.6    4.7   319   22.5 
2026-01-08 00:00 UT   09 51 35.5   -30 23 05    10.561   11.017  115.3    4.6   320   22.5 
2026-01-08 14:02 UT   09 51 26.2   -30 24 42    10.558   11.020  115.7    4.6   320   22.5 
2026-01-09 00:00 UT   09 51 19.5   -30 25 50    10.555   11.022  116.0    4.6   321   22.5 
2026-01-10 00:00 UT   09 51 03.1   -30 28 31    10.550   11.027  116.7    4.6   322   22.5 
2026-01-11 00:00 UT   09 50 46.5   -30 31 09    10.544   11.032  117.4    4.5   322   22.5 
2026-01-12 00:00 UT   09 50 29.6   -30 33 42    10.539   11.037  118.1    4.5   323   22.5 
2026-01-13 00:00 UT   09 50 12.4   -30 36 10    10.534   11.042  118.8    4.5   324   22.5 
2026-01-14 00:00 UT   09 49 54.9   -30 38 35    10.529   11.047  119.5    4.4   325   22.5 
2026-01-15 00:00 UT   09 49 37.2   -30 40 55    10.524   11.052  120.2    4.4   326   22.5 
2026-01-16 00:00 UT   09 49 19.2   -30 43 11    10.520   11.057  120.8    4.4   327   22.5 
2026-01-17 00:00 UT   09 49 00.9   -30 45 22    10.515   11.061  121.5    4.4   328   22.5 
2026-01-18 00:00 UT   09 48 42.5   -30 47 30    10.511   11.066  122.1    4.3   329   22.5 

    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.