C/2018 A4 (PANSTARRS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	14 Nov 2017	20.3	2.996 AU	2.065 AU	01h53m	+07°20'	156.2°	7.7°	60°
Perihelion	20 May 2018	20.4	2.387 AU	3.271 AU	05h31m	+23°06'	24.5°	10.1°	87°
Today	23 Dec 2025	31.9	15.226 AU	16.126 AU	16h26m	-20°09'	23.2°	1.5°	283°

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. (14.0 + 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/2018 A4 (PANSTARRS) are:

    e (Eccentricity)                : 0.8041630
    q (Perihelion distance)         : 2.3868650
    i (Inclination)                 : 3.15180
    Ω (Longitude of ascending node) : 97.56170
    ω (Argument of perihelion)      : 355.95760
    L (Longitude of perihelion)     : 93.52539
    B (Latitude of perihelion)      : -0.22207
    T (Time of perihelion passage)  : 2458258.73910
    P (Orbital period in years)     : 42.55

    Epoch                           : 2023 Sep 24
    Reference                       : MPEC 2023-J29

    Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); Halley type (P < 200 years)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-22 00:00 UT   16 26 08.2   -20 08 19    16.130   15.223   22.0    1.4   283   31.9 
2025-12-23 00:00 UT   16 26 24.7   -20 08 56    16.126   15.226   23.0    1.4   283   31.9 
2025-12-23 04:31 UT   16 26 27.8   -20 09 03    16.126   15.226   23.2    1.5   283   31.9 
2025-12-24 00:00 UT   16 26 41.1   -20 09 32    16.122   15.229   23.9    1.5   282   31.9 
2025-12-25 00:00 UT   16 26 57.5   -20 10 07    16.118   15.232   24.9    1.6   282   31.9 
2025-12-26 00:00 UT   16 27 13.7   -20 10 42    16.114   15.235   25.8    1.6   282   31.9 
2025-12-27 00:00 UT   16 27 29.8   -20 11 17    16.109   15.238   26.8    1.7   282   31.9 
2025-12-28 00:00 UT   16 27 45.8   -20 11 51    16.104   15.241   27.7    1.7   282   31.9 
2025-12-29 00:00 UT   16 28 01.6   -20 12 25    16.099   15.244   28.7    1.8   282   31.9 
2025-12-30 00:00 UT   16 28 17.4   -20 12 58    16.093   15.247   29.7    1.8   282   31.9 
2025-12-31 00:00 UT   16 28 33.0   -20 13 31    16.088   15.250   30.6    1.9   281   31.9 
2026-01-01 00:00 UT   16 28 48.5   -20 14 03    16.082   15.253   31.6    1.9   281   31.9 
2026-01-02 00:00 UT   16 29 03.9   -20 14 35    16.076   15.256   32.5    2.0   281   31.9 

    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.