C/2021 S1 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	30 Dec 2021	18.5	6.140 AU	5.300 AU	06h23m	+57°01'	146.1°	5.1°	175°
Perihelion	2 Mar 2022	18.7	6.125 AU	5.772 AU	05h56m	+49°30'	106.3°	8.9°	98°
Today	15 Jul 2025	22.2	10.161 AU	10.834 AU	09h17m	-18°26'	46.5°	4.2°	148°

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.)

The orbital elements of C/2021 S1 (ATLAS) are:

            e (Eccentricity)                : 1.0029070
            q (Perihelion distance)         : 6.1253640
            i (Inclination)                 : 52.03740
            Ω (Longitude of ascending node) : 299.85530
            ω (Argument of perihelion)      : 148.31240
            L (Longitude of perihelion)     : 279.06160
            B (Latitude of perihelion)      : 24.46537
            T (Time of perihelion passage)  : 2459640.52290

            Epoch                           : 2025 Jul 14
            Reference                       : MPEC 2023-J29

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

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. 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. (7.00 + 5 log[∆] + 10.00 log[r]).

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-07-15 00:00 UT   09 17 39.5   -18 24 47    10.823   10.157   47.0    4.2   147   22.2 
2025-07-15 20:43 UT   09 17 59.7   -18 26 20    10.834   10.161   46.5    4.2   148   22.2 
2025-07-16 00:00 UT   09 18 02.9   -18 26 34    10.836   10.162   46.4    4.2   148   22.2 
2025-07-17 00:00 UT   09 18 26.3   -18 28 25    10.848   10.167   45.8    4.1   149   22.2 
2025-07-18 00:00 UT   09 18 49.9   -18 30 19    10.861   10.172   45.3    4.1   150   22.3 
2025-07-19 00:00 UT   09 19 13.5   -18 32 15    10.873   10.176   44.7    4.0   151   22.3 
2025-07-20 00:00 UT   09 19 37.3   -18 34 14    10.885   10.181   44.2    4.0   152   22.3 
2025-07-21 00:00 UT   09 20 01.1   -18 36 16    10.897   10.186   43.7    3.9   153   22.3 
2025-07-22 00:00 UT   09 20 25.0   -18 38 22    10.908   10.191   43.1    3.9   154   22.3 
2025-07-23 00:00 UT   09 20 49.0   -18 40 29    10.920   10.196   42.6    3.9   155   22.3 
2025-07-24 00:00 UT   09 21 13.0   -18 42 40    10.931   10.201   42.1    3.8   156   22.3 
2025-07-25 00:00 UT   09 21 37.2   -18 44 54    10.942   10.205   41.6    3.8   157   22.3 

    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.