C/2021 Q4 (Fuls)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	9 Jun 2023	19.2	7.562 AU	7.682 AU	23h08m	+28°02'	79.5°	7.6°	250°
Nearest approach	17 Sep 2023	18.9	7.588 AU	6.689 AU	22h52m	+23°55'	151.4°	3.6°	156°
Today	16 Aug 2026	21.1	10.344 AU	9.802 AU	01h54m	-19°55'	119.9°	4.9°	265°

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. (6.0 + 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/2021 Q4 (Fuls) are:

    e (Eccentricity)                : 0.9998230
    q (Perihelion distance)         : 7.5619780
    i (Inclination)                 : 71.56430
    Ω (Longitude of ascending node) : 183.34150
    ω (Argument of perihelion)      : 146.97890
    L (Longitude of perihelion)     : 171.72699
    B (Latitude of perihelion)      : 31.12994
    T (Time of perihelion passage)  : 2460105.17760

    Epoch                           : 2026 Aug 13
    Reference                       : MPC194176

    Classification(s):              : Nearly isotropic; New (a > 10000 AU)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-08-15 00:00 UT   01 54 53.5   -19 46 16     9.816   10.337  118.4    4.9   264   21.1 
2026-08-16 00:00 UT   01 54 51.1   -19 51 23     9.808   10.341  119.2    4.9   265   21.1 
2026-08-16 19:51 UT   01 54 48.9   -19 55 37     9.802   10.344  119.9    4.9   265   21.1 
2026-08-17 00:00 UT   01 54 48.4   -19 56 30     9.800   10.344  120.0    4.9   265   21.1 
2026-08-18 00:00 UT   01 54 45.2   -20 01 38     9.793   10.348  120.8    4.8   266   21.1 
2026-08-19 00:00 UT   01 54 41.7   -20 06 48     9.785   10.352  121.6    4.8   267   21.1 
2026-08-20 00:00 UT   01 54 37.8   -20 11 58     9.778   10.356  122.4    4.7   268   21.1 
2026-08-21 00:00 UT   01 54 33.5   -20 17 08     9.771   10.360  123.2    4.7   268   21.1 
2026-08-22 00:00 UT   01 54 28.9   -20 22 19     9.764   10.364  124.0    4.6   269   21.1 
2026-08-23 00:00 UT   01 54 23.8   -20 27 31     9.757   10.368  124.8    4.6   270   21.1 
2026-08-24 00:00 UT   01 54 18.4   -20 32 43     9.751   10.372  125.6    4.5   271   21.1 
2026-08-25 00:00 UT   01 54 12.7   -20 37 56     9.744   10.376  126.4    4.5   271   21.1 
2026-08-26 00:00 UT   01 54 06.6   -20 43 08     9.738   10.380  127.1    4.5   272   21.1 

    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.