C/2021 U4 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	1 Nov 2021	19.7	1.899 AU	0.957 AU	02h37m	-11°36'	153.8°	13.3°	353°
Perihelion	23 Dec 2021	21.0	1.784 AU	1.945 AU	23h01m	-28°38'	65.8°	30.2°	75°
Today	13 Aug 2026	34.0	13.493 AU	13.613 AU	14h46m	-07°44'	81.0°	4.3°	106°

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)                : 0.9600810
    q (Perihelion distance)         : 1.7836370
    i (Inclination)                 : 152.86030
    Ω (Longitude of ascending node) : 241.78990
    ω (Argument of perihelion)      : 237.28240
    L (Longitude of perihelion)     : 187.61567
    B (Latitude of perihelion)      : -22.56859
    T (Time of perihelion passage)  : 2459571.60200
    P (Orbital period in years)     : 298.67

    Epoch                           : 2026 May 29
    Reference                       : MPC194177

    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
2026-08-12 00:00 UT   14 46 21.3   -07 43 38    13.574   13.483   82.7    4.3   106   34.0 
2026-08-13 00:00 UT   14 46 21.7   -07 44 00    13.597   13.488   81.7    4.3   106   34.0 
2026-08-13 17:45 UT   14 46 22.1   -07 44 17    13.613   13.493   81.0    4.3   106   34.0 
2026-08-14 00:00 UT   14 46 22.3   -07 44 24    13.619   13.494   80.8    4.2   106   34.0 
2026-08-15 00:00 UT   14 46 23.2   -07 44 48    13.641   13.500   79.8    4.2   106   34.0 
2026-08-16 00:00 UT   14 46 24.4   -07 45 14    13.663   13.505   78.9    4.2   106   34.0 
2026-08-17 00:00 UT   14 46 25.9   -07 45 40    13.686   13.511   77.9    4.2   106   34.0 
2026-08-18 00:00 UT   14 46 27.6   -07 46 08    13.708   13.517   77.0    4.2   106   34.0 
2026-08-19 00:00 UT   14 46 29.6   -07 46 37    13.730   13.522   76.1    4.2   105   34.0 
2026-08-20 00:00 UT   14 46 31.8   -07 47 07    13.752   13.528   75.1    4.1   105   34.0 
2026-08-21 00:00 UT   14 46 34.4   -07 47 37    13.774   13.533   74.2    4.1   105   34.0 
2026-08-22 00:00 UT   14 46 37.2   -07 48 09    13.796   13.539   73.2    4.1   105   34.0 
2026-08-23 00:00 UT   14 46 40.2   -07 48 42    13.817   13.545   72.3    4.1   105   34.0 

    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.