C/2021 O1 (Nishimura)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	6 Aug 2021	9.4	0.799 AU	1.687 AU	08h11m	+30°57'	19.0°	24.4°	316°
Perihelion	14 Aug 2021	9.3	0.783 AU	1.701 AU	09h07m	+28°54'	16.4°	21.4°	333°
Today	21 Nov 2025	26.6	14.054 AU	14.900 AU	17h26m	-41°54'	30.1°	2.0°	129°

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. This lightcurve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 9.2 + 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 O1 (Nishimura) are:

    e (Eccentricity)                : 0.9998840
    q (Perihelion distance)         : 0.7827140
    i (Inclination)                 : 27.55740
    Ω (Longitude of ascending node) : 41.51200
    ω (Argument of perihelion)      : 74.45830
    L (Longitude of perihelion)     : 114.09545
    B (Latitude of perihelion)      : 26.46948
    T (Time of perihelion passage)  : 2459441.44670
    P (Orbital period in years)     : 554265.27

    Epoch                           : 2025 Nov 12
    Reference                       : MPEC 2022-A21

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-11-20 00:00 UT   17 26 07.7   -41 55 14    14.876   14.043   31.5    2.1   127   26.6 
2025-11-21 00:00 UT   17 26 29.5   -41 55 06    14.889   14.049   30.7    2.1   128   26.6 
2025-11-21 20:34 UT   17 26 48.2   -41 54 60    14.900   14.054   30.1    2.0   129   26.6 
2025-11-22 00:00 UT   17 26 51.4   -41 54 59    14.902   14.055   30.0    2.0   129   26.6 
2025-11-23 00:00 UT   17 27 13.3   -41 54 53    14.914   14.062   29.3    2.0   130   26.6 
2025-11-24 00:00 UT   17 27 35.4   -41 54 48    14.927   14.068   28.6    1.9   132   26.6 
2025-11-25 00:00 UT   17 27 57.6   -41 54 44    14.939   14.074   27.9    1.9   133   26.6 
2025-11-26 00:00 UT   17 28 19.9   -41 54 41    14.951   14.081   27.2    1.8   134   26.6 
2025-11-27 00:00 UT   17 28 42.2   -41 54 39    14.962   14.087   26.5    1.8   136   26.6 
2025-11-28 00:00 UT   17 29 04.7   -41 54 39    14.974   14.093   25.9    1.8   137   26.6 
2025-11-29 00:00 UT   17 29 27.2   -41 54 39    14.985   14.099   25.3    1.7   139   26.6 
2025-11-30 00:00 UT   17 29 49.7   -41 54 41    14.996   14.106   24.6    1.7   140   26.6 
2025-12-01 00:00 UT   17 30 12.4   -41 54 43    15.006   14.112   24.0    1.6   142   26.6 

    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.