C/2019 S4 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	24 Nov 2019	19.0	3.660 AU	3.011 AU	01h36m	+72°28'	124.3°	12.9°	139°
Perihelion	9 Apr 2020	19.3	3.439 AU	3.820 AU	23h39m	+66°01'	60.5°	14.7°	333°
Today	11 May 2025	28.0	13.869 AU	12.906 AU	15h54m	-33°52'	161.7°	1.3°	328°

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.)

The orbital elements of C/2019 S4 (Lemmon) are:

            e (Eccentricity)                : 0.9861390
            q (Perihelion distance)         : 3.4394100
            i (Inclination)                 : 92.09840
            Ω (Longitude of ascending node) : 63.15640
            ω (Argument of perihelion)      : 71.37130
            L (Longitude of perihelion)     : 56.95714
            B (Latitude of perihelion)      : 71.25766
            T (Time of perihelion passage)  : 2458948.78930
            P (Orbital period in years)     : 3908.72

            Epoch                           : 2025 May 10
            Reference                       : MPEC 2021-S45

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

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. 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. (11.00 + 5 log[∆] + 10.00 log[r]).

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-05-11 00:00 UT   15 54 46.9   -33 52 47    12.905   13.865  161.2    1.3   326   28.0 
2025-05-11 16:49 UT   15 54 31.4   -33 52 52    12.906   13.869  161.7    1.3   328   28.0 
2025-05-12 00:00 UT   15 54 24.8   -33 52 54    12.907   13.871  161.9    1.3   328   28.0 
2025-05-13 00:00 UT   15 54 02.7   -33 52 59    12.909   13.876  162.6    1.3   331   28.0 
2025-05-14 00:00 UT   15 53 40.4   -33 53 03    12.911   13.882  163.2    1.2   334   28.0 
2025-05-15 00:00 UT   15 53 18.2   -33 53 06    12.914   13.888  163.8    1.2   337   28.0 
2025-05-16 00:00 UT   15 52 55.9   -33 53 06    12.917   13.893  164.3    1.1   340   28.0 
2025-05-17 00:00 UT   15 52 33.6   -33 53 06    12.920   13.899  164.8    1.1   344   28.0 
2025-05-18 00:00 UT   15 52 11.3   -33 53 04    12.923   13.904  165.3    1.1   347   28.0 
2025-05-19 00:00 UT   15 51 49.0   -33 53 01    12.927   13.910  165.7    1.0   351   28.0 
2025-05-20 00:00 UT   15 51 26.6   -33 52 56    12.931   13.915  166.0    1.0   355   28.0 
2025-05-21 00:00 UT   15 51 04.3   -33 52 50    12.935   13.921  166.2    1.0   360   28.0 

    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.