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°58'	19.0°	24.4°	316°
Perihelion	14 Aug 2021	9.3	0.783 AU	1.701 AU	09h06m	+28°55'	16.4°	21.4°	333°
Today	9 Oct 2025	26.4	13.779 AU	14.145 AU	17h13m	-42°17'	66.6°	3.8°	104°

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.)

The orbital elements of C/2021 O1 (Nishimura) are:

            e (Eccentricity)                : 0.9998730
            q (Perihelion distance)         : 0.7826630
            i (Inclination)                 : 27.56120
            Ω (Longitude of ascending node) : 41.52070
            ω (Argument of perihelion)      : 74.44840
            L (Longitude of perihelion)     : 114.09263
            B (Latitude of perihelion)      : 26.47173
            T (Time of perihelion passage)  : 2459441.40650
            P (Orbital period in years)     : 483789.71

            Epoch                           : 2025 Oct 08
            Reference                       : MPEC 2022-A21

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

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. The gray curve is based on the absolute magnitude and slope parameter as calculated from the original MPEC, or the latest values provided by the MPC (10.50 + 5 log[∆] + 10.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 9.22 + 5 log[∆] + 10.00 log[r]).

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-10-09 00:00 UT   17 13 37.5   -42 17 19    14.139   13.777   66.8    3.8   103   26.4 
2025-10-09 06:33 UT   17 13 41.0   -42 17 05    14.145   13.779   66.6    3.8   104   26.4 
2025-10-10 00:00 UT   17 13 50.4   -42 16 26    14.160   13.783   65.9    3.8   104   26.4 
2025-10-11 00:00 UT   17 14 03.5   -42 15 34    14.181   13.789   65.0    3.8   104   26.4 
2025-10-12 00:00 UT   17 14 17.0   -42 14 43    14.201   13.796   64.1    3.7   104   26.4 
2025-10-13 00:00 UT   17 14 30.7   -42 13 52    14.222   13.802   63.3    3.7   105   26.4 
2025-10-14 00:00 UT   17 14 44.8   -42 13 03    14.242   13.809   62.4    3.7   105   26.4 
2025-10-15 00:00 UT   17 14 59.1   -42 12 15    14.263   13.815   61.5    3.6   106   26.4 
2025-10-16 00:00 UT   17 15 13.7   -42 11 28    14.283   13.821   60.6    3.6   106   26.4 
2025-10-17 00:00 UT   17 15 28.5   -42 10 42    14.303   13.828   59.7    3.6   106   26.4 
2025-10-18 00:00 UT   17 15 43.7   -42 09 57    14.322   13.834   58.9    3.5   107   26.4 
2025-10-19 00:00 UT   17 15 59.1   -42 09 13    14.342   13.840   58.0    3.5   107   26.4 

    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.