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C/2019 S4 (Lemmon)
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach24 Nov 201919.03.660 AU3.011 AU01h37m+72°24'124.4°12.9°139°
Perihelion9 Apr 202019.33.438 AU3.820 AU23h40m+66°04'60.5°14.7°333°
Today15 Oct 202528.614.734 AU15.484 AU15h38m-33°26'39.9°2.5°121°
C/2019 S4 (Lemmon)- 2025-10-15
astro.vanbuitenen.nl


 
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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. (11.0 + 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/2019 S4 (Lemmon) are: 

    e (Eccentricity)                : 0.9862790
    q (Perihelion distance)         : 3.4383640
    i (Inclination)                 : 92.08730
    Ω (Longitude of ascending node) : 63.15380
    ω (Argument of perihelion)      : 71.36870
    L (Longitude of perihelion)     : 56.98799
    B (Latitude of perihelion)      : 71.25627
    T (Time of perihelion passage)  : 2458949.12640
    P (Orbital period in years)     : 3966.88

    Epoch                           : 2025 Oct 14
    Reference                       : MPEC 2021-S45

    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
2025-10-15 00:00 UT   15 38 09.0   -33 26 04    15.473   14.730   40.6    2.5   120   28.6 
2025-10-15 17:19 UT   15 38 19.2   -33 26 42    15.484   14.734   39.9    2.5   121   28.6 
2025-10-16 00:00 UT   15 38 23.1   -33 26 57    15.488   14.735   39.7    2.5   121   28.6 
2025-10-17 00:00 UT   15 38 37.4   -33 27 50    15.504   14.741   38.8    2.4   121   28.6 
2025-10-18 00:00 UT   15 38 51.8   -33 28 44    15.519   14.746   37.9    2.4   122   28.6 
2025-10-19 00:00 UT   15 39 06.4   -33 29 40    15.534   14.752   37.1    2.3   122   28.6 
2025-10-20 00:00 UT   15 39 21.1   -33 30 37    15.548   14.757   36.2    2.3   123   28.6 
2025-10-21 00:00 UT   15 39 36.0   -33 31 34    15.563   14.762   35.4    2.2   124   28.7 
2025-10-22 00:00 UT   15 39 51.0   -33 32 33    15.577   14.768   34.5    2.2   124   28.7 
2025-10-23 00:00 UT   15 40 06.1   -33 33 33    15.591   14.773   33.7    2.1   125   28.7 
2025-10-24 00:00 UT   15 40 21.3   -33 34 33    15.604   14.779   32.8    2.1   126   28.7 
2025-10-25 00:00 UT   15 40 36.6   -33 35 35    15.618   14.784   32.0    2.0   126   28.7 




    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.

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