C/2021 L3 (Borisov)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	24 Nov 2021	19.9	8.476 AU	8.329 AU	18h33m	+70°47'	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	17 Dec 2025	22.0	11.673 AU	11.477 AU	11h47m	+28°50'	99.1°	4.8°	292°

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)                : 1.0043300
    q (Perihelion distance)         : 8.4613400
    i (Inclination)                 : 78.52600
    Ω (Longitude of ascending node) : 345.02360
    ω (Argument of perihelion)      : 91.65830
    L (Longitude of perihelion)     : 263.30417
    B (Latitude of perihelion)      : 78.40837
    T (Time of perihelion passage)  : 2459625.48030

    Epoch                           : 2025 Dec 16
    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
2025-12-16 00:00 UT   11 47 34.0   +28 49 34    11.489   11.669   98.1    4.8   292   22.0 
2025-12-17 00:00 UT   11 47 32.1   +28 50 12    11.477   11.673   99.0    4.8   292   22.0 
2025-12-17 00:56 UT   11 47 32.0   +28 50 14    11.477   11.673   99.1    4.8   292   22.0 
2025-12-18 00:00 UT   11 47 29.8   +28 50 53    11.465   11.676  100.0    4.8   291   22.0 
2025-12-19 00:00 UT   11 47 27.1   +28 51 35    11.454   11.680  100.9    4.7   291   22.0 
2025-12-20 00:00 UT   11 47 24.1   +28 52 20    11.442   11.684  101.8    4.7   290   22.0 
2025-12-21 00:00 UT   11 47 20.6   +28 53 06    11.430   11.688  102.8    4.7   290   22.0 
2025-12-22 00:00 UT   11 47 16.7   +28 53 54    11.419   11.691  103.7    4.7   289   22.0 
2025-12-23 00:00 UT   11 47 12.5   +28 54 45    11.407   11.695  104.6    4.7   289   22.0 
2025-12-24 00:00 UT   11 47 07.8   +28 55 37    11.396   11.699  105.6    4.6   288   22.0 
2025-12-25 00:00 UT   11 47 02.8   +28 56 30    11.385   11.703  106.5    4.6   288   22.0 
2025-12-26 00:00 UT   11 46 57.3   +28 57 26    11.373   11.706  107.5    4.6   288   22.0 
2025-12-27 00:00 UT   11 46 51.5   +28 58 23    11.362   11.710  108.4    4.6   287   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.