C/2021 P4 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	13 Jul 2022	10.2	1.114 AU	1.957 AU	09h14m	+27°58'	24.4°	22.1°	81°
Perihelion	30 Jul 2022	10.0	1.078 AU	1.975 AU	09h59m	+14°19'	20.0°	18.8°	105°
Today	8 Dec 2025	28.3	11.576 AU	11.939 AU	22h14m	-44°09'	66.1°	4.5°	81°

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 8.0 + 5 log[∆] + 14.0 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/2021 P4 (ATLAS) are:

    e (Eccentricity)                : 0.9963850
    q (Perihelion distance)         : 1.0783730
    i (Inclination)                 : 56.40020
    Ω (Longitude of ascending node) : 347.98170
    ω (Argument of perihelion)      : 175.82050
    L (Longitude of perihelion)     : 345.66596
    B (Latitude of perihelion)      : 3.48026
    T (Time of perihelion passage)  : 2459791.00990
    P (Orbital period in years)     : 5152.18

    Epoch                           : 2025 Dec 08
    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
2025-12-07 00:00 UT   22 14 18.8   -44 16 30    11.903   11.563   67.6    4.5    80   28.3 
2025-12-08 00:00 UT   22 14 27.2   -44 12 50    11.923   11.570   66.8    4.5    80   28.3 
2025-12-08 19:28 UT   22 14 34.3   -44 09 51    11.939   11.576   66.1    4.5    81   28.3 
2025-12-09 00:00 UT   22 14 36.0   -44 09 10    11.943   11.577   66.0    4.5    81   28.3 
2025-12-10 00:00 UT   22 14 45.2   -44 05 29    11.962   11.584   65.2    4.4    81   28.3 
2025-12-11 00:00 UT   22 14 54.7   -44 01 49    11.982   11.590   64.4    4.4    82   28.3 
2025-12-12 00:00 UT   22 15 04.6   -43 58 08    12.001   11.597   63.6    4.4    83   28.3 
2025-12-13 00:00 UT   22 15 15.0   -43 54 28    12.021   11.604   62.8    4.3    83   28.3 
2025-12-14 00:00 UT   22 15 25.7   -43 50 47    12.040   11.610   62.0    4.3    84   28.4 
2025-12-15 00:00 UT   22 15 36.7   -43 47 07    12.059   11.617   61.2    4.3    84   28.4 
2025-12-16 00:00 UT   22 15 48.1   -43 43 27    12.078   11.624   60.4    4.2    85   28.4 
2025-12-17 00:00 UT   22 15 59.9   -43 39 47    12.097   11.631   59.6    4.2    86   28.4 
2025-12-18 00:00 UT   22 16 12.1   -43 36 07    12.116   11.637   58.8    4.1    86   28.4 

    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.