C/2021 A1 (Leonard) - DISINTEGRATED
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	12 Dec 2021	2.8	0.774 AU	0.232 AU	17h11m	-01°10'	22.0°	151.5°	355°
Perihelion	3 Jan 2022	5.9	0.615 AU	0.923 AU	21h39m	-35°30'	37.5°	76.6°	99°
Disintegration	1 Mar 2022	11.1	1.282 AU	1.994 AU	21h24m	-34°52'	33.0°	24.9°	220°
Today	18 May 2025	-	12.055 AU	11.080 AU	16h16m	-06°00'	163.8°	1.3°	213°

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.)

The orbital elements of C/2021 A1 (Leonard) are:

            e (Eccentricity)                : 1.0002360
            q (Perihelion distance)         : 0.6154930
            i (Inclination)                 : 132.75520
            Ω (Longitude of ascending node) : 255.91180
            ω (Argument of perihelion)      : 225.13870
            L (Longitude of perihelion)     : 221.61147
            B (Latitude of perihelion)      : -31.36286
            T (Time of perihelion passage)  : 2459583.26310

            Epoch                           : 2025 May 17
            Reference                       : MPEC 2025-A40

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

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. The gray curve is based on the absolute magnitude and slope parameter as calculated from the original MPEC, or the latest values provided by the MPC (8.50 + 5 log[∆] + 10.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 8.37 + 5 log[∆] + 11.03 log[r]). The additional green curve shows the effect of forward scattering, occurring when the comet is between the earth and the sun, for a gas-to-dust light ratio δ90 of 0.10. (See Marcus 2007)

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-05-18 00:00 UT   16 16 34.5   -06 00 39    11.079   12.053  163.7    1.4   214   25.5 
2025-05-18 06:26 UT   16 16 28.6   -06 00 15    11.080   12.055  163.8    1.3   213   25.5 
2025-05-19 00:00 UT   16 16 12.6   -05 59 11    11.084   12.060  164.1    1.3   210   25.5 
2025-05-20 00:00 UT   16 15 50.8   -05 57 45    11.089   12.067  164.4    1.3   206   25.5 
2025-05-21 00:00 UT   16 15 28.9   -05 56 20    11.094   12.074  164.6    1.3   202   25.5 
2025-05-22 00:00 UT   16 15 07.0   -05 54 56    11.100   12.080  164.8    1.3   199   25.5 
2025-05-23 00:00 UT   16 14 45.1   -05 53 34    11.107   12.087  164.9    1.3   195   25.5 
2025-05-24 00:00 UT   16 14 23.2   -05 52 13    11.113   12.094  164.9    1.2   191   25.5 
2025-05-25 00:00 UT   16 14 01.3   -05 50 53    11.120   12.101  164.9    1.3   187   25.5 
2025-05-26 00:00 UT   16 13 39.5   -05 49 35    11.127   12.108  164.7    1.3   183   25.5 
2025-05-27 00:00 UT   16 13 17.6   -05 48 18    11.134   12.114  164.6    1.3   179   25.5 
2025-05-28 00:00 UT   16 12 55.8   -05 47 03    11.142   12.121  164.3    1.3   175   25.6 

    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.