P/2021 R4 (Wierzchos)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	4 Oct 2021	20.4	2.337 AU	1.410 AU	00h04m	+31°56'	151.1°	11.9°	161°
Perihelion	13 Oct 2021	20.4	2.335 AU	1.418 AU	23h57m	+32°15'	149.8°	12.4°	140°
Today	8 Dec 2025	29.6	7.978 AU	8.136 AU	11h41m	-10°02'	77.3°	6.9°	291°

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. (16.0 + 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 P/2021 R4 (Wierzchos) are:

    e (Eccentricity)                : 0.5850500
    q (Perihelion distance)         : 2.3354300
    i (Inclination)                 : 21.00790
    Ω (Longitude of ascending node) : 321.27560
    ω (Argument of perihelion)      : 56.79060
    L (Longitude of perihelion)     : 16.23647
    B (Latitude of perihelion)      : 17.45430
    T (Time of perihelion passage)  : 2459500.54890
    P (Orbital period in years)     : 13.35

    Epoch                           : 2025 Nov 12
    Reference                       : MPEC 2021-W31

    Classification(s):              : Ecliptic; Jupiter family
    Tisserand (Jupiter)             : 2.499

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-07 00:00 UT   11 40 48.3   -09 56 38     8.164    7.974   75.4    6.9   291   29.6 
2025-12-08 00:00 UT   11 40 57.6   -09 59 42     8.150    7.976   76.4    6.9   291   29.6 
2025-12-08 23:36 UT   11 41 06.3   -10 02 40     8.136    7.978   77.3    6.9   291   29.6 
2025-12-09 00:00 UT   11 41 06.4   -10 02 43     8.136    7.978   77.3    6.9   291   29.6 
2025-12-10 00:00 UT   11 41 14.9   -10 05 42     8.122    7.980   78.3    6.9   291   29.6 
2025-12-11 00:00 UT   11 41 22.8   -10 08 39     8.107    7.982   79.2    7.0   292   29.6 
2025-12-12 00:00 UT   11 41 30.4   -10 11 34     8.093    7.984   80.2    7.0   292   29.6 
2025-12-13 00:00 UT   11 41 37.5   -10 14 26     8.079    7.986   81.1    7.0   292   29.6 
2025-12-14 00:00 UT   11 41 44.1   -10 17 17     8.064    7.988   82.1    7.0   292   29.6 
2025-12-15 00:00 UT   11 41 50.3   -10 20 04     8.050    7.991   83.0    7.0   292   29.6 
2025-12-16 00:00 UT   11 41 56.0   -10 22 50     8.035    7.993   84.0    7.0   293   29.6 
2025-12-17 00:00 UT   11 42 01.2   -10 25 33     8.021    7.995   85.0    7.0   293   29.5 
2025-12-18 00:00 UT   11 42 06.0   -10 28 14     8.006    7.997   85.9    7.1   293   29.5 

    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.