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'	18.9°	24.3°	316°
Perihelion	14 Aug 2021	9.3	0.783 AU	1.701 AU	09h06m	+28°56'	16.3°	21.4°	333°
Today	9 Aug 2025	26.0	13.389 AU	12.832 AU	17h11m	-43°32'	121.5°	3.7°	82°

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)                : 0.9998530
            q (Perihelion distance)         : 0.7826780
            i (Inclination)                 : 27.56720
            Ω (Longitude of ascending node) : 41.53440
            ω (Argument of perihelion)      : 74.43420
            L (Longitude of perihelion)     : 114.08973
            B (Latitude of perihelion)      : 26.47549
            T (Time of perihelion passage)  : 2459441.32200
            P (Orbital period in years)     : 388506.86

            Epoch                           : 2025 Aug 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 9.23 + 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
2025-08-09 00:00 UT   17 12 00.8   -43 33 30    12.821   13.386  122.0    3.7    82   26.0 
2025-08-09 12:36 UT   17 11 55.3   -43 32 47    12.832   13.389  121.5    3.7    82   26.0 
2025-08-10 00:00 UT   17 11 50.5   -43 32 08    12.841   13.393  121.1    3.7    82   26.0 
2025-08-11 00:00 UT   17 11 40.5   -43 30 45    12.861   13.399  120.2    3.7    83   26.0 
2025-08-12 00:00 UT   17 11 30.9   -43 29 23    12.881   13.405  119.3    3.8    83   26.0 
2025-08-13 00:00 UT   17 11 21.8   -43 27 59    12.901   13.412  118.4    3.8    84   26.1 
2025-08-14 00:00 UT   17 11 13.0   -43 26 36    12.921   13.418  117.4    3.8    84   26.1 
2025-08-15 00:00 UT   17 11 04.7   -43 25 12    12.941   13.425  116.5    3.9    84   26.1 
2025-08-16 00:00 UT   17 10 56.7   -43 23 49    12.962   13.431  115.6    3.9    85   26.1 
2025-08-17 00:00 UT   17 10 49.2   -43 22 25    12.982   13.438  114.7    3.9    85   26.1 
2025-08-18 00:00 UT   17 10 42.0   -43 21 01    13.003   13.444  113.8    4.0    86   26.1 
2025-08-19 00:00 UT   17 10 35.3   -43 19 36    13.024   13.451  112.9    4.0    86   26.1 

    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.