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°48'	153.7°	13.4°	353°
Perihelion	22 Dec 2021	21.0	1.787 AU	1.941 AU	23h01m	-28°45'	66.2°	30.2°	75°
Today	22 Jun 2025	32.5	11.039 AU	10.287 AU	15h04m	-11°00'	135.8°	3.7°	112°

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)                : 0.9607130
            q (Perihelion distance)         : 1.7872970
            i (Inclination)                 : 152.88260
            Ω (Longitude of ascending node) : 241.80560
            ω (Argument of perihelion)      : 237.32340
            L (Longitude of perihelion)     : 187.58315
            B (Latitude of perihelion)      : -22.56144
            T (Time of perihelion passage)  : 2459571.05900
            P (Orbital period in years)     : 306.85

            Epoch                           : 2025 Jun 21
            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
2025-06-22 00:00 UT   15 04 49.4   -11 00 31    10.283   11.037  136.1    3.7   112   32.5 
2025-06-22 06:08 UT   15 04 44.6   -11 00 10    10.287   11.039  135.8    3.7   112   32.5 
2025-06-23 00:00 UT   15 04 30.5   -10 59 11    10.301   11.044  135.0    3.7   112   32.5 
2025-06-24 00:00 UT   15 04 12.0   -10 57 53    10.319   11.050  134.0    3.8   112   32.5 
2025-06-25 00:00 UT   15 03 53.8   -10 56 37    10.337   11.056  133.0    3.9   112   32.5 
2025-06-26 00:00 UT   15 03 35.9   -10 55 22    10.356   11.062  132.0    3.9   112   32.5 
2025-06-27 00:00 UT   15 03 18.4   -10 54 09    10.375   11.068  131.0    4.0   112   32.5 
2025-06-28 00:00 UT   15 03 01.2   -10 52 58    10.394   11.075  129.9    4.0   111   32.5 
2025-06-29 00:00 UT   15 02 44.4   -10 51 49    10.413   11.081  128.9    4.1   111   32.5 
2025-06-30 00:00 UT   15 02 27.8   -10 50 42    10.433   11.087  127.9    4.1   111   32.5 
2025-07-01 00:00 UT   15 02 11.7   -10 49 36    10.453   11.093  126.9    4.2   111   32.5 
2025-07-02 00:00 UT   15 01 55.9   -10 48 32    10.472   11.099  125.9    4.3   111   32.6 

    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.