C/2020 A3 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	2 May 2019	19.1	5.767 AU	4.954 AU	13h11m	-50°56'	140.5°	6.4°	33°
Perihelion	26 Jun 2019	19.3	5.754 AU	5.424 AU	12h11m	-40°43'	103.9°	9.9°	109°
Today	12 Dec 2025	25.8	15.738 AU	14.887 AU	07h36m	+29°43'	148.8°	1.9°	266°

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. (8.0 + 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/2020 A3 (ATLAS) are:

    e (Eccentricity)                : 0.9984180
    q (Perihelion distance)         : 5.7536000
    i (Inclination)                 : 146.61520
    Ω (Longitude of ascending node) : 120.79610
    ω (Argument of perihelion)      : 268.22070
    L (Longitude of perihelion)     : 32.92672
    B (Latitude of perihelion)      : -33.36660
    T (Time of perihelion passage)  : 2458660.66700
    P (Orbital period in years)     : 219330.88

    Epoch                           : 2025 Dec 12
    Reference                       : MPEC 2023-A50

    Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); External (P > 200 years)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-11 00:00 UT   07 36 53.3   +29 40 37    14.894   15.729  146.9    2.0   267   25.8 
2025-12-12 00:00 UT   07 36 34.8   +29 42 02    14.890   15.733  147.9    1.9   266   25.8 
2025-12-12 21:15 UT   07 36 18.3   +29 43 18    14.887   15.738  148.8    1.9   266   25.8 
2025-12-13 00:00 UT   07 36 16.1   +29 43 28    14.886   15.738  149.0    1.8   266   25.8 
2025-12-14 00:00 UT   07 35 57.3   +29 44 53    14.883   15.743  150.0    1.8   265   25.8 
2025-12-15 00:00 UT   07 35 38.2   +29 46 18    14.879   15.748  151.0    1.7   265   25.8 
2025-12-16 00:00 UT   07 35 19.0   +29 47 43    14.876   15.753  152.1    1.7   264   25.8 
2025-12-17 00:00 UT   07 34 59.6   +29 49 07    14.873   15.758  153.1    1.6   263   25.8 
2025-12-18 00:00 UT   07 34 40.0   +29 50 31    14.871   15.763  154.1    1.6   262   25.8 
2025-12-19 00:00 UT   07 34 20.3   +29 51 54    14.869   15.768  155.2    1.5   261   25.8 
2025-12-20 00:00 UT   07 34 00.4   +29 53 17    14.867   15.772  156.2    1.4   260   25.8 
2025-12-21 00:00 UT   07 33 40.4   +29 54 40    14.865   15.777  157.2    1.4   259   25.8 
2025-12-22 00:00 UT   07 33 20.2   +29 56 02    14.864   15.782  158.2    1.3   258   25.8 

    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.