421P/McNaught
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	22 May 2020	20.2	2.938 AU	2.026 AU	13h57m	-07°58'	148.8°	10.3°	117°
Perihelion	22 Jan 2021	18.3	1.652 AU	2.613 AU	20h58m	-23°38'	9.9°	5.9°	113°
Today	11 Nov 2025	27.8	8.341 AU	8.196 AU	09h18m	+25°54'	95.0°	6.8°	287°

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)                : 0.6743730
    q (Perihelion distance)         : 1.6522480
    i (Inclination)                 : 10.07500
    Ω (Longitude of ascending node) : 55.31950
    ω (Argument of perihelion)      : 259.84350
    L (Longitude of perihelion)     : 135.00732
    B (Latitude of perihelion)      : -9.91551
    T (Time of perihelion passage)  : 2459237.35410
    P (Orbital period in years)     : 11.43

    Epoch                           : 2025 Nov 10
    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
2025-11-10 00:00 UT   09 18 41.0   +25 52 50     8.223    8.340   93.3    6.8   287   27.8 
2025-11-11 00:00 UT   09 18 46.1   +25 53 48     8.208    8.341   94.3    6.8   287   27.8 
2025-11-11 17:06 UT   09 18 49.4   +25 54 31     8.196    8.341   95.0    6.8   287   27.8 
2025-11-12 00:00 UT   09 18 50.7   +25 54 49     8.192    8.342   95.3    6.8   287   27.8 
2025-11-13 00:00 UT   09 18 54.7   +25 55 52     8.176    8.343   96.3    6.8   287   27.8 
2025-11-14 00:00 UT   09 18 58.3   +25 56 57     8.160    8.344   97.3    6.8   287   27.8 
2025-11-15 00:00 UT   09 19 01.3   +25 58 05     8.145    8.344   98.2    6.7   287   27.8 
2025-11-16 00:00 UT   09 19 03.8   +25 59 15     8.129    8.345   99.2    6.7   286   27.8 
2025-11-17 00:00 UT   09 19 05.7   +26 00 28     8.114    8.346  100.2    6.7   286   27.8 
2025-11-18 00:00 UT   09 19 07.1   +26 01 43     8.098    8.347  101.2    6.7   286   27.8 
2025-11-19 00:00 UT   09 19 08.0   +26 03 01     8.083    8.348  102.2    6.6   286   27.8 
2025-11-20 00:00 UT   09 19 08.3   +26 04 20     8.067    8.349  103.2    6.6   286   27.8 
2025-11-21 00:00 UT   09 19 08.1   +26 05 43     8.052    8.350  104.2    6.6   285   27.7 

    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.