123P/West-Hartley
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	21 Sep 2026	17.0	2.159 AU	3.059 AU	10h59m	+17°41'	21.8°	9.9°	320°
Today	10 Oct 2026	16.9	2.163 AU	2.987 AU	11h38m	+13°32'	28.6°	12.8°	313°
Nearest approach	17 Apr 2027	17.2	2.656 AU	1.679 AU	14h47m	-12°06'	163.3°	6.2°	274°

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 8.8 + 5 log[∆] + 17.2 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 123P/West-Hartley are:

    e (Eccentricity)                : 0.4446890
    q (Perihelion distance)         : 2.1587470
    i (Inclination)                 : 15.28140
    Ω (Longitude of ascending node) : 45.84750
    ω (Argument of perihelion)      : 103.87590
    L (Longitude of perihelion)     : 330.21130
    B (Latitude of perihelion)      : 14.82506
    T (Time of perihelion passage)  : 2461305.36940
    P (Orbital period in years)     : 7.66

    Epoch                           : 2026 Oct 09
    Reference                       : MPEC 2026-N12

    Classification(s):              : Ecliptic; Jupiter family
    Tisserand (Jupiter)             : 2.832

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-10-09 00:00 UT   11 36 05.5   +13 48 30     2.992    2.163   28.2   12.6   314   16.9 
2026-10-10 00:00 UT   11 38 09.5   +13 34 46     2.987    2.163   28.5   12.7   313   16.9 
2026-10-10 03:27 UT   11 38 27.2   +13 32 48     2.987    2.163   28.6   12.8   313   16.9 
2026-10-11 00:00 UT   11 40 13.0   +13 21 02     2.983    2.164   28.9   12.9   313   16.9 
2026-10-12 00:00 UT   11 42 16.3   +13 07 18     2.979    2.164   29.3   13.1   313   16.9 
2026-10-13 00:00 UT   11 44 19.3   +12 53 34     2.974    2.165   29.7   13.2   312   16.9 
2026-10-14 00:00 UT   11 46 21.9   +12 39 51     2.970    2.166   30.1   13.4   312   16.9 
2026-10-15 00:00 UT   11 48 24.2   +12 26 07     2.965    2.166   30.5   13.5   312   16.9 
2026-10-16 00:00 UT   11 50 26.2   +12 12 24     2.960    2.167   31.0   13.7   311   16.9 
2026-10-17 00:00 UT   11 52 27.8   +11 58 41     2.956    2.168   31.4   13.8   311   16.9 
2026-10-18 00:00 UT   11 54 29.1   +11 44 59     2.951    2.168   31.8   14.0   311   16.9 
2026-10-19 00:00 UT   11 56 30.1   +11 31 18     2.946    2.169   32.2   14.2   310   16.9 
2026-10-20 00:00 UT   11 58 30.8   +11 17 38     2.942    2.170   32.6   14.3   310   16.9 

    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.