C/2021 O1 (Nishimura)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	6 Aug 2021	9.4	0.800 AU	1.687 AU	08h11m	+30°57'	19.1°	24.5°	316°
Perihelion	15 Aug 2021	9.3	0.783 AU	1.701 AU	09h07m	+28°52'	16.4°	21.4°	333°
Today	29 May 2026	26.8	15.234 AU	14.337 AU	17h47m	-44°54'	151.3°	1.8°	317°

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)                : 1.0002590
    q (Perihelion distance)         : 0.7832670
    i (Inclination)                 : 27.52790
    Ω (Longitude of ascending node) : 41.48850
    ω (Argument of perihelion)      : 74.49480
    L (Longitude of perihelion)     : 114.11672
    B (Latitude of perihelion)      : 26.44637
    T (Time of perihelion passage)  : 2459441.64660

    Epoch                           : 2026 May 29
    Reference                       : MPC194175

    Classification(s):              : Nearly isotropic; New (a > 10000 AU)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-05-28 00:00 UT   17 48 19.9   -44 53 26    14.336   15.222  150.0    1.9   314   26.8 
2026-05-29 00:00 UT   17 48 00.0   -44 53 59    14.336   15.228  150.7    1.9   316   26.8 
2026-05-29 21:46 UT   17 47 41.9   -44 54 27    14.337   15.234  151.3    1.8   317   26.8 
2026-05-30 00:00 UT   17 47 40.1   -44 54 30    14.337   15.235  151.4    1.8   317   26.8 
2026-05-31 00:00 UT   17 47 20.0   -44 54 59    14.338   15.241  152.0    1.8   319   26.8 
2026-06-01 00:00 UT   17 46 59.7   -44 55 27    14.339   15.247  152.6    1.8   321   26.8 
2026-06-02 00:00 UT   17 46 39.4   -44 55 52    14.340   15.253  153.2    1.7   323   26.8 
2026-06-03 00:00 UT   17 46 19.0   -44 56 17    14.342   15.259  153.8    1.7   325   26.8 
2026-06-04 00:00 UT   17 45 58.4   -44 56 39    14.344   15.265  154.3    1.6   327   26.8 
2026-06-05 00:00 UT   17 45 37.8   -44 56 60    14.346   15.271  154.9    1.6   329   26.8 
2026-06-06 00:00 UT   17 45 17.1   -44 57 19    14.348   15.277  155.4    1.6   331   26.8 
2026-06-07 00:00 UT   17 44 56.3   -44 57 36    14.351   15.283  155.8    1.6   333   26.8 
2026-06-08 00:00 UT   17 44 35.4   -44 57 51    14.354   15.289  156.2    1.5   336   26.8 

    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.