C/2020 R4 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	1 Mar 2021	10.7	1.019 AU	1.708 AU	20h39m	-11°29'	32.3°	31.3°	266°
Nearest approach	23 Apr 2021	9.2	1.337 AU	0.460 AU	16h14m	+28°54'	127.7°	36.5°	222°
Today	24 May 2026	29.8	15.673 AU	16.160 AU	08h14m	+15°03'	59.6°	3.2°	106°

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)                : 0.9893440
    q (Perihelion distance)         : 1.0193070
    i (Inclination)                 : 164.38650
    Ω (Longitude of ascending node) : 323.21390
    ω (Argument of perihelion)      : 46.45480
    L (Longitude of perihelion)     : 277.83561
    B (Latitude of perihelion)      : 11.24974
    T (Time of perihelion passage)  : 2459275.14600
    P (Orbital period in years)     : 935.55

    Epoch                           : 2026 May 23
    Reference                       : MPC194169

    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
2026-05-23 00:00 UT   08 14 44.1   +15 03 53    16.128   15.664   61.1    3.2   105   29.8 
2026-05-24 00:00 UT   08 14 50.3   +15 03 43    16.149   15.670   60.1    3.2   105   29.8 
2026-05-24 12:41 UT   08 14 53.6   +15 03 37    16.160   15.673   59.6    3.2   106   29.8 
2026-05-25 00:00 UT   08 14 56.7   +15 03 32    16.169   15.676   59.2    3.2   106   29.8 
2026-05-26 00:00 UT   08 15 03.3   +15 03 20    16.190   15.681   58.3    3.1   106   29.8 
2026-05-27 00:00 UT   08 15 10.0   +15 03 08    16.210   15.687   57.3    3.1   106   29.8 
2026-05-28 00:00 UT   08 15 17.0   +15 02 55    16.230   15.693   56.4    3.1   106   29.8 
2026-05-29 00:00 UT   08 15 24.1   +15 02 41    16.250   15.698   55.5    3.0   106   29.8 
2026-05-30 00:00 UT   08 15 31.5   +15 02 26    16.269   15.704   54.6    3.0   106   29.8 
2026-05-31 00:00 UT   08 15 39.0   +15 02 10    16.289   15.710   53.6    3.0   106   29.9 
2026-06-01 00:00 UT   08 15 46.6   +15 01 54    16.308   15.715   52.7    2.9   106   29.9 
2026-06-02 00:00 UT   08 15 54.5   +15 01 36    16.327   15.721   51.8    2.9   107   29.9 
2026-06-03 00:00 UT   08 16 02.5   +15 01 18    16.346   15.727   50.9    2.9   107   29.9 

    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.