C/2019 S4 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	24 Nov 2019	19.0	3.660 AU	3.010 AU	01h37m	+72°21'	124.5°	12.9°	139°
Perihelion	9 Apr 2020	19.3	3.437 AU	3.820 AU	23h41m	+66°07'	60.4°	14.7°	333°
Today	12 Mar 2026	28.8	15.530 AU	15.251 AU	16h03m	-37°20'	104.5°	3.6°	286°

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)                : 0.9864210
    q (Perihelion distance)         : 3.4371990
    i (Inclination)                 : 92.06850
    Ω (Longitude of ascending node) : 63.14000
    ω (Argument of perihelion)      : 71.37590
    L (Longitude of perihelion)     : 57.02676
    B (Latitude of perihelion)      : 71.26543
    T (Time of perihelion passage)  : 2458949.44650
    P (Orbital period in years)     : 4027.22

    Epoch                           : 2026 Mar 11
    Reference                       : MPEC 2026-E44

    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
2026-03-11 00:00 UT   16 03 39.5   -37 18 55    15.265   15.523  103.2    3.6   286   28.8 
2026-03-12 00:00 UT   16 03 32.8   -37 20 24    15.254   15.529  104.2    3.6   286   28.8 
2026-03-12 06:50 UT   16 03 30.9   -37 20 49    15.251   15.530  104.5    3.6   286   28.8 
2026-03-13 00:00 UT   16 03 25.9   -37 21 51    15.244   15.534  105.2    3.5   286   28.8 
2026-03-14 00:00 UT   16 03 18.6   -37 23 18    15.233   15.539  106.2    3.5   287   28.8 
2026-03-15 00:00 UT   16 03 11.0   -37 24 43    15.222   15.545  107.1    3.5   287   28.8 
2026-03-16 00:00 UT   16 03 03.0   -37 26 08    15.212   15.550  108.1    3.5   287   28.8 
2026-03-17 00:00 UT   16 02 54.8   -37 27 31    15.202   15.555  109.1    3.5   288   28.8 
2026-03-18 00:00 UT   16 02 46.2   -37 28 53    15.191   15.561  110.0    3.4   288   28.8 
2026-03-19 00:00 UT   16 02 37.3   -37 30 14    15.181   15.566  111.0    3.4   288   28.8 
2026-03-20 00:00 UT   16 02 28.0   -37 31 34    15.171   15.571  112.0    3.4   289   28.8 
2026-03-21 00:00 UT   16 02 18.5   -37 32 53    15.161   15.577  112.9    3.4   289   28.8 
2026-03-22 00:00 UT   16 02 08.6   -37 34 11    15.151   15.582  113.9    3.4   289   28.8 

    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.