C/2021 U4 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	31 Oct 2021	19.7	1.901 AU	0.959 AU	02h37m	-11°47'	153.7°	13.4°	353°
Perihelion	22 Dec 2021	21.0	1.787 AU	1.941 AU	23h01m	-28°44'	66.2°	30.2°	75°
Today	19 Jul 2025	32.7	11.205 AU	10.835 AU	14h58m	-10°35'	108.8°	4.9°	109°

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 U4 (Leonard) are:

            e (Eccentricity)                : 0.9607250
            q (Perihelion distance)         : 1.7871460
            i (Inclination)                 : 152.88190
            Ω (Longitude of ascending node) : 241.80520
            ω (Argument of perihelion)      : 237.32170
            L (Longitude of perihelion)     : 187.58470
            B (Latitude of perihelion)      : -22.56156
            T (Time of perihelion passage)  : 2459571.09130
            P (Orbital period in years)     : 306.95

            Epoch                           : 2025 Jul 17
            Reference                       : MPEC 2021-W31

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

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 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. (17.00 + 5 log[∆] + 10.00 log[r]).

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
2025-07-19 00:00 UT   14 58 22.2   -10 35 04    10.834   11.205  108.9    4.9   109   32.7 
2025-07-19 01:16 UT   14 58 21.7   -10 35 02    10.835   11.205  108.8    4.9   109   32.7 
2025-07-20 00:00 UT   14 58 12.9   -10 34 32    10.856   11.211  107.9    4.9   109   32.7 
2025-07-21 00:00 UT   14 58 04.1   -10 34 03    10.878   11.217  106.9    5.0   108   32.7 
2025-07-22 00:00 UT   14 57 55.5   -10 33 35    10.901   11.223  105.9    5.0   108   32.7 
2025-07-23 00:00 UT   14 57 47.4   -10 33 09    10.924   11.229  105.0    5.0   108   32.7 
2025-07-24 00:00 UT   14 57 39.6   -10 32 44    10.946   11.235  104.0    5.0   108   32.7 
2025-07-25 00:00 UT   14 57 32.2   -10 32 21    10.969   11.242  103.0    5.1   108   32.7 
2025-07-26 00:00 UT   14 57 25.1   -10 32 00    10.992   11.248  102.0    5.1   108   32.7 
2025-07-27 00:00 UT   14 57 18.5   -10 31 41    11.015   11.254  101.0    5.1   108   32.7 
2025-07-28 00:00 UT   14 57 12.2   -10 31 24    11.038   11.260  100.1    5.1   108   32.7 
2025-07-29 00:00 UT   14 57 06.2   -10 31 08    11.061   11.266   99.1    5.1   108   32.7 

    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.