C/2021 U4 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	1 Nov 2021	19.7	1.901 AU	0.959 AU	02h37m	-11°45'	153.7°	13.4°	353°
Perihelion	22 Dec 2021	21.0	1.787 AU	1.942 AU	23h01m	-28°43'	66.1°	30.2°	75°
Today	17 Sep 2025	33.1	11.572 AU	12.168 AU	14h59m	-10°46'	51.7°	3.9°	102°

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)                : 0.9607580
            q (Perihelion distance)         : 1.7866590
            i (Inclination)                 : 152.87950
            Ω (Longitude of ascending node) : 241.80400
            ω (Argument of perihelion)      : 237.31590
            L (Longitude of perihelion)     : 187.59014
            B (Latitude of perihelion)      : -22.56196
            T (Time of perihelion passage)  : 2459571.18740
            P (Orbital period in years)     : 307.21

            Epoch                           : 2025 Sep 16
            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
2025-09-17 00:00 UT   14 59 12.8   -10 46 48    12.167   11.572   51.7    3.9   102   33.1 
2025-09-17 00:57 UT   14 59 13.2   -10 46 50    12.168   11.572   51.7    3.9   102   33.1 
2025-09-18 00:00 UT   14 59 22.6   -10 47 33    12.186   11.578   50.8    3.9   102   33.1 
2025-09-19 00:00 UT   14 59 32.6   -10 48 18    12.205   11.584   49.9    3.8   101   33.1 
2025-09-20 00:00 UT   14 59 42.8   -10 49 03    12.224   11.590   49.0    3.7   101   33.1 
2025-09-21 00:00 UT   14 59 53.2   -10 49 50    12.243   11.596   48.0    3.7   101   33.1 
2025-09-22 00:00 UT   15 00 03.8   -10 50 36    12.261   11.602   47.1    3.6   101   33.1 
2025-09-23 00:00 UT   15 00 14.7   -10 51 24    12.280   11.608   46.2    3.6   101   33.1 
2025-09-24 00:00 UT   15 00 25.8   -10 52 11    12.298   11.614   45.3    3.5   100   33.1 
2025-09-25 00:00 UT   15 00 37.0   -10 52 60    12.316   11.620   44.4    3.5   100   33.1 
2025-09-26 00:00 UT   15 00 48.5   -10 53 48    12.334   11.626   43.4    3.4   100   33.1 
2025-09-27 00:00 UT   15 01 00.2   -10 54 38    12.351   11.632   42.5    3.3   100   33.1 

    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.