421P/McNaught
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	22 May 2020	20.2	2.939 AU	2.026 AU	13h57m	-07°57'	148.8°	10.3°	117°
Perihelion	22 Jan 2021	18.3	1.652 AU	2.614 AU	20h58m	-23°37'	9.8°	5.8°	113°
Today	21 Oct 2025	27.9	8.321 AU	8.533 AU	09h15m	+25°42'	74.4°	6.6°	290°

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 421P/McNaught are:

    e (Eccentricity)                : 0.6743680
    q (Perihelion distance)         : 1.6523160
    i (Inclination)                 : 10.07510
    Ω (Longitude of ascending node) : 55.32170
    ω (Argument of perihelion)      : 259.84560
    L (Longitude of perihelion)     : 135.01165
    B (Latitude of perihelion)      : -9.91568
    T (Time of perihelion passage)  : 2459237.46870
    P (Orbital period in years)     : 11.43

    Epoch                           : 2025 Oct 20
    Reference                       : MPEC 2021-W31

    Classification(s):              : Ecliptic; Jupiter family
    Tisserand (Jupiter)             : 2.461

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-10-20 00:00 UT   09 15 02.1   +25 41 54     8.550    8.320   73.4    6.6   290   27.9 
2025-10-21 00:00 UT   09 15 17.1   +25 42 02     8.535    8.321   74.3    6.6   290   27.9 
2025-10-21 02:27 UT   09 15 18.7   +25 42 02     8.533    8.321   74.4    6.6   290   27.9 
2025-10-22 00:00 UT   09 15 31.7   +25 42 11     8.519    8.322   75.2    6.6   290   27.9 
2025-10-23 00:00 UT   09 15 45.8   +25 42 23     8.504    8.322   76.2    6.7   290   27.9 
2025-10-24 00:00 UT   09 15 59.5   +25 42 37     8.489    8.323   77.1    6.7   290   27.8 
2025-10-25 00:00 UT   09 16 12.8   +25 42 54     8.474    8.324   78.0    6.7   290   27.8 
2025-10-26 00:00 UT   09 16 25.6   +25 43 13     8.458    8.325   79.0    6.7   290   27.8 
2025-10-27 00:00 UT   09 16 37.9   +25 43 34     8.443    8.326   79.9    6.7   289   27.8 
2025-10-28 00:00 UT   09 16 49.8   +25 43 58     8.427    8.327   80.9    6.8   289   27.8 
2025-10-29 00:00 UT   09 17 01.2   +25 44 24     8.412    8.328   81.8    6.8   289   27.8 
2025-10-30 00:00 UT   09 17 12.2   +25 44 53     8.396    8.329   82.8    6.8   289   27.8 
2025-10-31 00:00 UT   09 17 22.7   +25 45 24     8.381    8.330   83.7    6.8   289   27.8 

    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.