C/2023 H2 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	29 Oct 2023	8.6	0.895 AU	0.500 AU	13h30m	+50°07'	64.0°	85.9°	349°
Nearest approach	10 Nov 2023	6.5	0.925 AU	0.192 AU	18h41m	+18°49'	64.7°	104.4°	60°
Today	29 May 2025	23.0	6.833 AU	6.419 AU	01h50m	-87°49'	110.0°	8.0°	218°

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/2023 H2 (Lemmon) are:

            e (Eccentricity)                : 0.9963780
            q (Perihelion distance)         : 0.8952240
            i (Inclination)                 : 113.74820
            Ω (Longitude of ascending node) : 217.07050
            ω (Argument of perihelion)      : 150.68510
            L (Longitude of perihelion)     : 229.81263
            B (Latitude of perihelion)      : 26.62512
            T (Time of perihelion passage)  : 2460246.66060
            P (Orbital period in years)     : 3885.75

            Epoch                           : 2025 May 27
            Reference                       : MPEC 2024-GJ3

            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 gray curve is based on the absolute magnitude and slope parameter as calculated from the original MPEC, or the latest values provided by the MPC (14.00 + 5 log[∆] + 10.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 10.57 + 5 log[∆] + 10.00 log[r]). The additional green curve shows the effect of forward scattering, occurring when the comet is between the earth and the sun, for a gas-to-dust light ratio δ90 of 0.30. (See Marcus 2007)

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
2025-05-29 00:00 UT   01 42 18.7   -87 42 20     6.415    6.826  109.8    8.0   220   22.9 
2025-05-29 19:41 UT   01 50 44.4   -87 49 07     6.419    6.833  110.0    8.0   218   23.0 
2025-05-30 00:00 UT   01 52 41.4   -87 50 36     6.420    6.834  110.0    8.0   218   23.0 
2025-05-31 00:00 UT   02 04 16.7   -87 58 41     6.425    6.843  110.2    8.0   216   23.0 
2025-06-01 00:00 UT   02 17 17.8   -88 06 31     6.431    6.851  110.4    8.0   214   23.0 
2025-06-02 00:00 UT   02 32 00.2   -88 14 02     6.436    6.860  110.6    8.0   211   23.0 
2025-06-03 00:00 UT   02 48 41.3   -88 21 11     6.442    6.869  110.8    7.9   208   23.0 
2025-06-04 00:00 UT   03 07 40.2   -88 27 50     6.448    6.877  111.0    7.9   205   23.0 
2025-06-05 00:00 UT   03 29 15.6   -88 33 53     6.454    6.886  111.2    7.9   200   23.0 
2025-06-06 00:00 UT   03 53 42.3   -88 39 12     6.460    6.894  111.3    7.9   195   23.0 
2025-06-07 00:00 UT   04 21 06.0   -88 43 36     6.466    6.903  111.5    7.9   190   23.0 
2025-06-08 00:00 UT   04 51 16.2   -88 46 55     6.473    6.911  111.6    7.8   183   23.0 

    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.