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	15 Feb 2022	19.9	8.461 AU	8.428 AU	19h37m	+72°55'	88.6°	6.7°	327°
Today	1 Nov 2025	22.0	11.503 AU	11.987 AU	11h43m	+29°03'	58.7°	4.2°	312°

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)                : 1.0044170
    q (Perihelion distance)         : 8.4610280
    i (Inclination)                 : 78.52900
    Ω (Longitude of ascending node) : 345.02210
    ω (Argument of perihelion)      : 91.65660
    L (Longitude of perihelion)     : 263.29640
    B (Latitude of perihelion)      : 78.41158
    T (Time of perihelion passage)  : 2459625.50530

    Epoch                           : 2025 Oct 31
    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
2025-10-31 00:00 UT   11 42 48.6   +29 05 17    12.001   11.498   57.5    4.2   313   22.0 
2025-11-01 00:00 UT   11 43 01.3   +29 03 55    11.992   11.501   58.3    4.2   313   22.0 
2025-11-01 11:18 UT   11 43 07.3   +29 03 18    11.987   11.503   58.7    4.2   312   22.0 
2025-11-02 00:00 UT   11 43 13.9   +29 02 36    11.983   11.505   59.1    4.2   312   22.0 
2025-11-03 00:00 UT   11 43 26.1   +29 01 21    11.973   11.509   60.0    4.3   311   22.0 
2025-11-04 00:00 UT   11 43 38.2   +29 00 07    11.964   11.513   60.8    4.3   311   22.0 
2025-11-05 00:00 UT   11 43 50.0   +28 58 57    11.954   11.516   61.6    4.3   310   22.0 
2025-11-06 00:00 UT   11 44 01.6   +28 57 49    11.945   11.520   62.5    4.4   310   22.0 
2025-11-07 00:00 UT   11 44 12.9   +28 56 45    11.935   11.524   63.3    4.4   309   22.0 
2025-11-08 00:00 UT   11 44 23.9   +28 55 43    11.925   11.527   64.1    4.4   309   22.0 
2025-11-09 00:00 UT   11 44 34.7   +28 54 43    11.915   11.531   65.0    4.5   308   22.0 
2025-11-10 00:00 UT   11 44 45.2   +28 53 47    11.904   11.535   65.8    4.5   308   22.0 
2025-11-11 00:00 UT   11 44 55.5   +28 52 53    11.894   11.538   66.7    4.5   307   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.