123P/West-Hartley
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Today	17 Oct 2025	18.6	3.214 AU	2.419 AU	04h22m	+25°05'	136.3°	12.4°	257°
Perihelion	22 Sep 2026	14.8	2.158 AU	3.057 AU	11h00m	+17°38'	21.8°	10.0°	320°
Nearest approach	17 Apr 2027	15.7	2.654 AU	1.677 AU	14h47m	-12°09'	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. 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. (4.0 + 5 log[∆] + 25.0 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 123P/West-Hartley are:

    e (Eccentricity)                : 0.4445910
    q (Perihelion distance)         : 2.1579090
    i (Inclination)                 : 15.28750
    Ω (Longitude of ascending node) : 45.88080
    ω (Argument of perihelion)      : 103.93930
    L (Longitude of perihelion)     : -29.68956
    B (Latitude of perihelion)      : 14.82681
    T (Time of perihelion passage)  : 2461305.62680
    P (Orbital period in years)     : 7.66

    Epoch                           : 2025 Oct 16
    Reference                       : MPC188417

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-10-16 00:00 UT   04 22 46.3   +24 58 38     2.445    3.222  134.4   12.8   257   18.6 
2025-10-17 00:00 UT   04 22 27.5   +25 02 21     2.431    3.218  135.4   12.6   257   18.6 
2025-10-17 19:54 UT   04 22 10.8   +25 05 26     2.419    3.214  136.3   12.4   257   18.6 
2025-10-18 00:00 UT   04 22 07.3   +25 06 04     2.417    3.213  136.5   12.3   257   18.6 
2025-10-19 00:00 UT   04 21 45.5   +25 09 44     2.403    3.209  137.5   12.1   257   18.6 
2025-10-20 00:00 UT   04 21 22.3   +25 13 23     2.390    3.205  138.6   11.9   256   18.5 
2025-10-21 00:00 UT   04 20 57.5   +25 17 01     2.376    3.200  139.7   11.6   256   18.5 
2025-10-22 00:00 UT   04 20 31.3   +25 20 36     2.363    3.196  140.7   11.4   256   18.5 
2025-10-23 00:00 UT   04 20 03.6   +25 24 10     2.350    3.192  141.8   11.1   255   18.5 
2025-10-24 00:00 UT   04 19 34.5   +25 27 42     2.337    3.188  142.9   10.9   255   18.4 
2025-10-25 00:00 UT   04 19 03.9   +25 31 11     2.325    3.183  144.0   10.6   255   18.4 
2025-10-26 00:00 UT   04 18 31.8   +25 34 38     2.313    3.179  145.1   10.3   254   18.4 
2025-10-27 00:00 UT   04 17 58.3   +25 38 03     2.300    3.175  146.1   10.0   254   18.4 

    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.