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	5.423 AU	12h11m	-40°44'	104.0°	9.9°	109°
Today	24 Dec 2025	25.8	15.797 AU	14.862 AU	07h32m	+30°00'	161.2°	1.2°	254°

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)                : 0.9983900
    q (Perihelion distance)         : 5.7536930
    i (Inclination)                 : 146.61500
    Ω (Longitude of ascending node) : 120.79600
    ω (Argument of perihelion)      : 268.22030
    L (Longitude of perihelion)     : 32.92710
    B (Latitude of perihelion)      : -33.36679
    T (Time of perihelion passage)  : 2458660.61660
    P (Orbital period in years)     : 213639.33

    Epoch                           : 2025 Dec 24
    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
2025-12-23 00:00 UT   07 32 59.9   +29 57 24    14.863   15.787  159.2    1.3   257   25.8 
2025-12-24 00:00 UT   07 32 39.5   +29 58 45    14.862   15.792  160.2    1.2   256   25.8 
2025-12-24 23:07 UT   07 32 19.7   +30 00 02    14.862   15.797  161.2    1.2   254   25.8 
2025-12-25 00:00 UT   07 32 19.0   +30 00 05    14.862   15.797  161.2    1.1   254   25.8 
2025-12-26 00:00 UT   07 31 58.3   +30 01 25    14.862   15.802  162.2    1.1   252   25.8 
2025-12-27 00:00 UT   07 31 37.6   +30 02 44    14.862   15.807  163.1    1.0   251   25.8 
2025-12-28 00:00 UT   07 31 16.7   +30 04 03    14.863   15.811  164.1    1.0   249   25.9 
2025-12-29 00:00 UT   07 30 55.8   +30 05 21    14.864   15.816  165.0    0.9   246   25.9 
2025-12-30 00:00 UT   07 30 34.8   +30 06 39    14.865   15.821  165.9    0.9   244   25.9 
2025-12-31 00:00 UT   07 30 13.7   +30 07 55    14.867   15.826  166.8    0.8   241   25.9 
2026-01-01 00:00 UT   07 29 52.6   +30 09 11    14.869   15.831  167.6    0.8   238   25.9 
2026-01-02 00:00 UT   07 29 31.4   +30 10 27    14.871   15.836  168.4    0.7   234   25.9 
2026-01-03 00:00 UT   07 29 10.1   +30 11 41    14.874   15.841  169.1    0.7   230   25.9 

    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.