C/2021 L3 (Borisov)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	24 Nov 2021	19.9	8.478 AU	8.331 AU	18h33m	+70°48'	95.2°	6.7°	36°
Perihelion	14 Feb 2022	19.9	8.464 AU	8.429 AU	19h36m	+72°55'	88.7°	6.7°	327°
Today	4 Oct 2026	22.7	12.799 AU	13.645 AU	11h25m	+20°57'	31.1°	2.3°	322°

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)                : 1.0036620
    q (Perihelion distance)         : 8.4636160
    i (Inclination)                 : 78.51070
    Ω (Longitude of ascending node) : 345.02970
    ω (Argument of perihelion)      : 91.66740
    L (Longitude of perihelion)     : 263.34432
    B (Latitude of perihelion)      : 78.39195
    T (Time of perihelion passage)  : 2459625.14650

    Epoch                           : 2026 Oct 03
    Reference                       : MPC194175

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-10-03 00:00 UT   11 25 03.3   +21 00 35    13.649   12.793   30.1    2.2   323   22.7 
2026-10-04 00:00 UT   11 25 17.8   +20 58 11    13.646   12.797   30.8    2.3   322   22.7 
2026-10-04 08:29 UT   11 25 23.0   +20 57 20    13.645   12.799   31.1    2.3   322   22.7 
2026-10-05 00:00 UT   11 25 32.3   +20 55 48    13.642   12.801   31.6    2.3   321   22.7 
2026-10-06 00:00 UT   11 25 46.7   +20 53 27    13.638   12.805   32.4    2.4   321   22.7 
2026-10-07 00:00 UT   11 26 01.0   +20 51 07    13.634   12.809   33.2    2.4   320   22.7 
2026-10-08 00:00 UT   11 26 15.1   +20 48 50    13.630   12.813   34.0    2.5   319   22.7 
2026-10-09 00:00 UT   11 26 29.2   +20 46 34    13.625   12.817   34.8    2.5   318   22.7 
2026-10-10 00:00 UT   11 26 43.1   +20 44 19    13.620   12.821   35.6    2.6   317   22.8 
2026-10-11 00:00 UT   11 26 56.9   +20 42 07    13.615   12.825   36.4    2.6   317   22.8 
2026-10-12 00:00 UT   11 27 10.6   +20 39 56    13.610   12.829   37.2    2.7   316   22.8 
2026-10-13 00:00 UT   11 27 24.1   +20 37 47    13.604   12.833   38.0    2.7   315   22.8 
2026-10-14 00:00 UT   11 27 37.5   +20 35 40    13.598   12.837   38.9    2.8   315   22.8 

    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.