C/2024 J4 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	25 Apr 2025	19.1	5.695 AU	5.052 AU	16h21m	+31°39'	125.5°	8.3°	219°
Nearest approach	13 May 2025	19.1	5.696 AU	5.008 AU	15h58m	+31°56'	128.8°	7.9°	192°
Today	16 Nov 2025	19.8	5.881 AU	6.732 AU	14h53m	+08°31'	28.4°	4.6°	344°

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. (8.0 + 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/2024 J4 (Lemmon) are:

    e (Eccentricity)                : 0.9990470
    q (Perihelion distance)         : 5.6950790
    i (Inclination)                 : 117.52500
    Ω (Longitude of ascending node) : 19.31050
    ω (Argument of perihelion)      : 127.85600
    L (Longitude of perihelion)     : 50.04540
    B (Latitude of perihelion)      : 44.44187
    T (Time of perihelion passage)  : 2460791.45920
    P (Orbital period in years)     : 461966.28

    Epoch                           : 2025 Nov 15
    Reference                       : MPC188411

    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
2025-11-15 00:00 UT   14 53 12.6   +08 38 21     6.735    5.879   27.9    4.5   346   19.8 
2025-11-16 00:00 UT   14 53 30.7   +08 33 29     6.733    5.881   28.3    4.6   344   19.8 
2025-11-16 08:36 UT   14 53 37.1   +08 31 45     6.732    5.881   28.4    4.6   344   19.8 
2025-11-17 00:00 UT   14 53 48.7   +08 28 41     6.731    5.883   28.7    4.6   343   19.8 
2025-11-18 00:00 UT   14 54 06.6   +08 23 57     6.728    5.884   29.1    4.7   341   19.8 
2025-11-19 00:00 UT   14 54 24.5   +08 19 17     6.725    5.886   29.6    4.8   339   19.8 
2025-11-20 00:00 UT   14 54 42.2   +08 14 41     6.722    5.888   30.1    4.8   338   19.8 
2025-11-21 00:00 UT   14 54 59.9   +08 10 09     6.718    5.890   30.6    4.9   336   19.8 
2025-11-22 00:00 UT   14 55 17.4   +08 05 41     6.715    5.892   31.2    5.0   335   19.8 
2025-11-23 00:00 UT   14 55 34.8   +08 01 17     6.711    5.893   31.7    5.1   333   19.8 
2025-11-24 00:00 UT   14 55 52.0   +07 56 57     6.707    5.895   32.3    5.1   332   19.8 
2025-11-25 00:00 UT   14 56 09.2   +07 52 41     6.702    5.897   32.8    5.2   331   19.8 
2025-11-26 00:00 UT   14 56 26.1   +07 48 29     6.697    5.899   33.4    5.3   329   19.8 

    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.