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°	22.2°	81°
Perihelion	30 Jul 2022	10.0	1.078 AU	1.975 AU	09h59m	+14°19'	20.0°	18.8°	105°
Today	16 Oct 2025	27.9	11.211 AU	10.821 AU	22h17m	-47°03'	110.6°	4.8°	50°

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)                : 0.9963720
    q (Perihelion distance)         : 1.0783990
    i (Inclination)                 : 56.39210
    Ω (Longitude of ascending node) : 347.98980
    ω (Argument of perihelion)      : 175.81530
    L (Longitude of perihelion)     : 345.67068
    B (Latitude of perihelion)      : 3.48426
    T (Time of perihelion passage)  : 2459790.97850
    P (Orbital period in years)     : 5124.70

    Epoch                           : 2025 Oct 15
    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
2025-10-16 00:00 UT   22 17 41.7   -47 03 38    10.819   11.210  110.6    4.8    50   27.9 
2025-10-16 02:00 UT   22 17 40.3   -47 03 26    10.821   11.211  110.6    4.8    50   27.9 
2025-10-17 00:00 UT   22 17 25.1   -47 01 16    10.839   11.217  109.8    4.8    51   27.9 
2025-10-18 00:00 UT   22 17 09.1   -46 58 52    10.859   11.224  109.0    4.8    51   27.9 
2025-10-19 00:00 UT   22 16 53.5   -46 56 25    10.879   11.231  108.2    4.8    52   27.9 
2025-10-20 00:00 UT   22 16 38.4   -46 53 54    10.899   11.238  107.4    4.9    53   27.9 
2025-10-21 00:00 UT   22 16 23.9   -46 51 21    10.920   11.245  106.6    4.9    53   28.0 
2025-10-22 00:00 UT   22 16 09.8   -46 48 46    10.940   11.251  105.7    4.9    54   28.0 
2025-10-23 00:00 UT   22 15 56.2   -46 46 07    10.960   11.258  104.9    4.9    55   28.0 
2025-10-24 00:00 UT   22 15 43.1   -46 43 26    10.981   11.265  104.1    4.9    55   28.0 
2025-10-25 00:00 UT   22 15 30.6   -46 40 42    11.001   11.272  103.3    4.9    56   28.0 
2025-10-26 00:00 UT   22 15 18.5   -46 37 55    11.022   11.279  102.4    4.9    56   28.0 

    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.