C/2021 U4 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	1 Nov 2021	19.7	1.900 AU	0.959 AU	02h37m	-11°43'	153.7°	13.4°	353°
Perihelion	22 Dec 2021	21.0	1.786 AU	1.943 AU	23h01m	-28°42'	66.0°	30.2°	75°
Today	17 Jan 2026	33.4	12.305 AU	12.687 AU	15h26m	-11°46'	65.1°	4.2°	288°

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.)

Light curve

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations from COBS. 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. (17.0 + 5 log[∆] + 10.0 log[r]). An additional green curve is displayed when an increase in apparent brightness is expected due to forward scattering of sunlight, which occurs when a dust-rich comet is located between the Earth and the Sun. (See Marcus 2007)

Charts

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.

Orbital elements

The orbital elements of C/2021 U4 (Leonard) are:

    e (Eccentricity)                : 0.9607810
    q (Perihelion distance)         : 1.7860680
    i (Inclination)                 : 152.87610
    Ω (Longitude of ascending node) : 241.80210
    ω (Argument of perihelion)      : 237.30730
    L (Longitude of perihelion)     : 187.59804
    B (Latitude of perihelion)      : -22.56242
    T (Time of perihelion passage)  : 2459571.27730
    P (Orbital period in years)     : 307.33

    Epoch                           : 2025 Nov 12
    Reference                       : MPEC 2021-W31

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-01-16 00:00 UT   15 25 59.8   -11 47 20    12.702   12.296   63.5    4.1   288   33.4 
2026-01-17 00:00 UT   15 26 06.0   -11 46 52    12.692   12.302   64.5    4.1   288   33.4 
2026-01-17 12:49 UT   15 26 09.2   -11 46 37    12.687   12.305   65.1    4.2   288   33.4 
2026-01-18 00:00 UT   15 26 11.9   -11 46 23    12.682   12.308   65.5    4.2   288   33.4 
2026-01-19 00:00 UT   15 26 17.6   -11 45 53    12.672   12.314   66.5    4.2   287   33.4 
2026-01-20 00:00 UT   15 26 22.9   -11 45 21    12.662   12.320   67.5    4.2   287   33.4 
2026-01-21 00:00 UT   15 26 28.0   -11 44 48    12.652   12.325   68.5    4.3   287   33.4 
2026-01-22 00:00 UT   15 26 32.8   -11 44 13    12.641   12.331   69.5    4.3   287   33.4 
2026-01-23 00:00 UT   15 26 37.2   -11 43 37    12.631   12.337   70.5    4.3   287   33.4 
2026-01-24 00:00 UT   15 26 41.4   -11 42 59    12.620   12.343   71.5    4.3   287   33.4 
2026-01-25 00:00 UT   15 26 45.3   -11 42 20    12.609   12.349   72.5    4.4   287   33.4 
2026-01-26 00:00 UT   15 26 48.8   -11 41 40    12.598   12.355   73.5    4.4   286   33.4 
2026-01-27 00:00 UT   15 26 52.1   -11 40 58    12.587   12.361   74.5    4.4   286   33.4 

    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.