C/2021 G1 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	20 Jul 2021	22.4	3.429 AU	4.079 AU	10h54m	+47°25'	44.5°	12.0°	69°
Nearest approach	11 Jan 2022	22.1	3.774 AU	2.936 AU	08h55m	+54°18'	143.8°	8.8°	214°
Today	21 Oct 2025	30.0	11.888 AU	11.173 AU	04h20m	-13°11'	134.2°	3.4°	299°

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. (14.0 + 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 G1 (Leonard) are:

    e (Eccentricity)                : 0.9516300
    q (Perihelion distance)         : 3.4293090
    i (Inclination)                 : 131.54680
    Ω (Longitude of ascending node) : 270.69760
    ω (Argument of perihelion)      : 107.44480
    L (Longitude of perihelion)     : 335.34595
    B (Latitude of perihelion)      : 45.56064
    T (Time of perihelion passage)  : 2459415.59500
    P (Orbital period in years)     : 596.96

    Epoch                           : 2025 Oct 20
    Reference                       : MPEC 2021-J72

    Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); External (P > 200 years)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-10-20 00:00 UT   04 21 03.2   -13 07 50    11.175   11.881  133.4    3.5   298   30.0 
2025-10-21 00:00 UT   04 20 43.2   -13 11 10    11.173   11.887  134.0    3.5   299   30.0 
2025-10-21 04:55 UT   04 20 39.0   -13 11 51    11.173   11.888  134.2    3.4   299   30.0 
2025-10-22 00:00 UT   04 20 22.9   -13 14 28    11.171   11.892  134.7    3.4   300   30.0 
2025-10-23 00:00 UT   04 20 02.4   -13 17 44    11.169   11.898  135.3    3.4   302   30.0 
2025-10-24 00:00 UT   04 19 41.7   -13 20 58    11.168   11.904  136.0    3.3   303   30.0 
2025-10-25 00:00 UT   04 19 20.7   -13 24 09    11.167   11.909  136.6    3.3   304   30.0 
2025-10-26 00:00 UT   04 18 59.5   -13 27 19    11.166   11.915  137.2    3.3   306   30.0 
2025-10-27 00:00 UT   04 18 38.1   -13 30 26    11.165   11.921  137.8    3.2   307   30.0 
2025-10-28 00:00 UT   04 18 16.4   -13 33 31    11.165   11.926  138.4    3.2   308   30.0 
2025-10-29 00:00 UT   04 17 54.6   -13 36 33    11.165   11.932  138.9    3.1   310   30.0 
2025-10-30 00:00 UT   04 17 32.6   -13 39 33    11.165   11.937  139.4    3.1   311   30.0 
2025-10-31 00:00 UT   04 17 10.3   -13 42 30    11.165   11.943  140.0    3.1   313   30.0 

    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.