C/2021 U4 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	31 Oct 2021	19.7	1.901 AU	0.960 AU	02h36m	-11°52'	153.6°	13.4°	353°
Perihelion	22 Dec 2021	21.0	1.788 AU	1.940 AU	23h01m	-28°47'	66.3°	30.2°	75°
Today	30 Apr 2025	32.2	10.702 AU	9.720 AU	15h26m	-12°39'	166.4°	1.3°	259°

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)                : 0.9598980
            q (Perihelion distance)         : 1.7881020
            i (Inclination)                 : 152.88620
            Ω (Longitude of ascending node) : 241.80460
            ω (Argument of perihelion)      : 237.34670
            L (Longitude of perihelion)     : 187.55696
            B (Latitude of perihelion)      : -22.56473
            T (Time of perihelion passage)  : 2459570.92200
            P (Orbital period in years)     : 297.74

            Epoch                           : 2025 Feb 02
            Reference                       : MPEC 2025-AH4

            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
2025-04-30 00:00 UT   15 26 24.3   -12 40 55     9.718   10.698  165.8    1.3   260   32.2 
2025-04-30 13:55 UT   15 26 08.9   -12 39 36     9.720   10.702  166.4    1.3   259   32.2 
2025-05-01 00:00 UT   15 25 57.6   -12 38 38     9.721   10.705  166.8    1.2   258   32.2 
2025-05-02 00:00 UT   15 25 30.9   -12 36 21     9.724   10.711  167.8    1.1   256   32.2 
2025-05-03 00:00 UT   15 25 04.0   -12 34 04     9.727   10.717  168.7    1.1   253   32.2 
2025-05-04 00:00 UT   15 24 37.2   -12 31 47     9.730   10.723  169.6    1.0   250   32.2 
2025-05-05 00:00 UT   15 24 10.2   -12 29 30     9.734   10.730  170.5    0.9   246   32.2 
2025-05-06 00:00 UT   15 23 43.3   -12 27 14     9.738   10.736  171.3    0.8   242   32.3 
2025-05-07 00:00 UT   15 23 16.3   -12 24 59     9.742   10.742  172.0    0.7   236   32.3 
2025-05-08 00:00 UT   15 22 49.3   -12 22 43     9.746   10.749  172.7    0.7   230   32.3 
2025-05-09 00:00 UT   15 22 22.3   -12 20 29     9.751   10.755  173.3    0.6   223   32.3 
2025-05-10 00:00 UT   15 21 55.3   -12 18 15     9.757   10.761  173.7    0.6   214   32.3 

    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.