C/2020 R4 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	2 Mar 2021	10.7	1.020 AU	1.705 AU	20h40m	-11°25'	32.6°	31.5°	266°
Nearest approach	23 Apr 2021	9.2	1.336 AU	0.459 AU	16h15m	+29°00'	127.6°	36.6°	222°
Today	19 Dec 2025	29.2	14.773 AU	14.028 AU	08h41m	+13°19'	137.9°	2.6°	290°

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 9.4 + 5 log[∆] + 12.0 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 R4 (ATLAS) are:

    e (Eccentricity)                : 0.9894400
    q (Perihelion distance)         : 1.0198730
    i (Inclination)                 : 164.39550
    Ω (Longitude of ascending node) : 323.22430
    ω (Argument of perihelion)      : 46.48470
    L (Longitude of perihelion)     : 277.81482
    B (Latitude of perihelion)      : 11.24899
    T (Time of perihelion passage)  : 2459275.54040
    P (Orbital period in years)     : 949.12

    Epoch                           : 2025 Nov 12
    Reference                       : MPEC 2022-K19

    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
2025-12-18 00:00 UT   08 41 44.6   +13 18 29    14.036   14.765  136.4    2.6   290   29.2 
2025-12-19 00:00 UT   08 41 29.9   +13 19 05    14.030   14.771  137.5    2.6   290   29.2 
2025-12-19 08:22 UT   08 41 24.7   +13 19 18    14.028   14.773  137.9    2.6   290   29.2 
2025-12-20 00:00 UT   08 41 14.9   +13 19 42    14.024   14.777  138.6    2.5   290   29.2 
2025-12-21 00:00 UT   08 40 59.8   +13 20 20    14.019   14.783  139.6    2.5   291   29.2 
2025-12-22 00:00 UT   08 40 44.5   +13 20 60    14.014   14.789  140.7    2.4   291   29.2 
2025-12-23 00:00 UT   08 40 29.0   +13 21 40    14.009   14.795  141.8    2.4   291   29.2 
2025-12-24 00:00 UT   08 40 13.3   +13 22 21    14.004   14.800  142.9    2.3   291   29.2 
2025-12-25 00:00 UT   08 39 57.4   +13 23 04    13.999   14.806  143.9    2.2   292   29.2 
2025-12-26 00:00 UT   08 39 41.3   +13 23 47    13.995   14.812  145.0    2.2   292   29.2 
2025-12-27 00:00 UT   08 39 25.1   +13 24 31    13.991   14.818  146.1    2.1   292   29.2 
2025-12-28 00:00 UT   08 39 08.6   +13 25 16    13.988   14.824  147.2    2.1   292   29.2 
2025-12-29 00:00 UT   08 38 52.1   +13 26 02    13.984   14.830  148.2    2.0   293   29.2 

    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.