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	27 Jul 2026	25.6	10.152 AU	9.809 AU	13h56m	-76°39'	106.9°	5.5°	102°

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
2026-07-26 00:00 UT   13 56 28.4   -76 49 40     9.784   10.139  107.7    5.5   100   25.6 
2026-07-27 00:00 UT   13 56 37.2   -76 43 35     9.798   10.147  107.3    5.5   101   25.6 
2026-07-27 17:45 UT   13 56 44.6   -76 39 06     9.809   10.152  106.9    5.5   102   25.6 
2026-07-28 00:00 UT   13 56 47.4   -76 37 31     9.813   10.154  106.8    5.5   102   25.6 
2026-07-29 00:00 UT   13 56 59.1   -76 31 30     9.828   10.161  106.3    5.5   103   25.6 
2026-07-30 00:00 UT   13 57 12.1   -76 25 31     9.843   10.168  105.9    5.5   104   25.6 
2026-07-31 00:00 UT   13 57 26.5   -76 19 35     9.858   10.175  105.4    5.5   105   25.6 
2026-08-01 00:00 UT   13 57 42.2   -76 13 41     9.873   10.183  104.9    5.5   105   25.6 
2026-08-02 00:00 UT   13 57 59.2   -76 07 50     9.888   10.190  104.5    5.5   106   25.6 
2026-08-03 00:00 UT   13 58 17.5   -76 02 01     9.904   10.197  104.0    5.5   107   25.6 
2026-08-04 00:00 UT   13 58 36.9   -75 56 15     9.919   10.204  103.5    5.5   108   25.6 
2026-08-05 00:00 UT   13 58 57.6   -75 50 32     9.935   10.211  103.0    5.6   109   25.6 
2026-08-06 00:00 UT   13 59 19.4   -75 44 51     9.950   10.219  102.5    5.6   109   25.7 

    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.