C/2021 L3 (Borisov)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	24 Nov 2021	19.9	8.475 AU	8.329 AU	18h33m	+70°46'	95.2°	6.7°	36°
Perihelion	14 Feb 2022	19.9	8.461 AU	8.428 AU	19h37m	+72°55'	88.6°	6.7°	327°
Today	2 Dec 2025	22.0	11.619 AU	11.648 AU	11h47m	+28°44'	85.9°	4.9°	298°

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. (6.0 + 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 C/2021 L3 (Borisov) are:

    e (Eccentricity)                : 1.0043610
    q (Perihelion distance)         : 8.4612370
    i (Inclination)                 : 78.52690
    Ω (Longitude of ascending node) : 345.02310
    ω (Argument of perihelion)      : 91.65780
    L (Longitude of perihelion)     : 263.30184
    B (Latitude of perihelion)      : 78.40934
    T (Time of perihelion passage)  : 2459625.49020

    Epoch                           : 2025 Dec 01
    Reference                       : MPEC 2024-H50

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-01 00:00 UT   11 47 17.3   +28 44 35    11.668   11.613   84.3    4.8   299   22.0 
2025-12-02 00:00 UT   11 47 21.0   +28 44 38    11.656   11.617   85.3    4.9   298   22.0 
2025-12-02 17:37 UT   11 47 23.4   +28 44 42    11.648   11.619   85.9    4.9   298   22.0 
2025-12-03 00:00 UT   11 47 24.3   +28 44 44    11.644   11.620   86.2    4.9   298   22.0 
2025-12-04 00:00 UT   11 47 27.2   +28 44 52    11.632   11.624   87.1    4.9   297   22.0 
2025-12-05 00:00 UT   11 47 29.8   +28 45 02    11.620   11.628   88.0    4.9   297   22.0 
2025-12-06 00:00 UT   11 47 32.0   +28 45 15    11.608   11.632   88.9    4.9   296   22.0 
2025-12-07 00:00 UT   11 47 33.9   +28 45 30    11.596   11.635   89.8    4.9   296   22.0 
2025-12-08 00:00 UT   11 47 35.4   +28 45 48    11.584   11.639   90.7    4.9   296   22.0 
2025-12-09 00:00 UT   11 47 36.5   +28 46 08    11.572   11.643   91.6    4.9   295   22.0 
2025-12-10 00:00 UT   11 47 37.3   +28 46 31    11.560   11.646   92.6    4.8   295   22.0 
2025-12-11 00:00 UT   11 47 37.7   +28 46 56    11.548   11.650   93.5    4.8   294   22.0 
2025-12-12 00:00 UT   11 47 37.7   +28 47 23    11.537   11.654   94.4    4.8   294   22.0 

    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.