C/2023 H2 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	29 Oct 2023	8.6	0.896 AU	0.500 AU	13h30m	+50°10'	64.1°	85.8°	349°
Nearest approach	11 Nov 2023	6.5	0.925 AU	0.192 AU	18h41m	+18°53'	64.9°	104.3°	60°
Today	26 Sep 2026	26.0	10.582 AU	10.802 AU	14h34m	-72°11'	74.7°	5.2°	142°

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. This lightcurve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 10.6 + 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/2023 H2 (Lemmon) are:

    e (Eccentricity)                : 0.9964410
    q (Perihelion distance)         : 0.8957440
    i (Inclination)                 : 113.72490
    Ω (Longitude of ascending node) : 217.13050
    ω (Argument of perihelion)      : 150.72670
    L (Longitude of perihelion)     : 229.84030
    B (Latitude of perihelion)      : 26.59311
    T (Time of perihelion passage)  : 2460246.69020
    P (Orbital period in years)     : 3992.86

    Epoch                           : 2026 May 29
    Reference                       : MPC194184

    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
2026-09-25 00:00 UT   14 33 56.5   -72 14 09    10.785   10.575   75.3    5.3   141   26.0 
2026-09-26 00:00 UT   14 34 50.8   -72 11 32    10.801   10.582   74.7    5.2   142   26.0 
2026-09-26 01:02 UT   14 34 53.1   -72 11 26    10.802   10.582   74.7    5.2   142   26.0 
2026-09-27 00:00 UT   14 35 45.4   -72 08 59    10.818   10.589   74.2    5.2   143   26.0 
2026-09-28 00:00 UT   14 36 40.3   -72 06 29    10.834   10.596   73.7    5.2   143   26.0 
2026-09-29 00:00 UT   14 37 35.5   -72 04 03    10.850   10.603   73.1    5.2   144   26.0 
2026-09-30 00:00 UT   14 38 30.9   -72 01 41    10.867   10.610   72.6    5.2   145   26.0 
2026-10-01 00:00 UT   14 39 26.7   -71 59 23    10.883   10.617   72.1    5.1   145   26.0 
2026-10-02 00:00 UT   14 40 22.7   -71 57 08    10.899   10.625   71.5    5.1   146   26.0 
2026-10-03 00:00 UT   14 41 18.9   -71 54 57    10.915   10.632   71.0    5.1   146   26.0 
2026-10-04 00:00 UT   14 42 15.4   -71 52 50    10.931   10.639   70.5    5.1   147   26.0 
2026-10-05 00:00 UT   14 43 12.2   -71 50 46    10.947   10.646   69.9    5.1   148   26.0 
2026-10-06 00:00 UT   14 44 09.2   -71 48 46    10.962   10.653   69.4    5.0   148   26.0 

    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.