121P/Shoemaker-Holt
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	12 Dec 2022	20.4	3.814 AU	2.837 AU	05h06m	+14°52'	171.5°	2.2°	15°
Perihelion	1 Jul 2023	21.3	3.736 AU	4.746 AU	07h03m	+25°56'	5.9°	1.6°	62°
Today	24 Jul 2026	23.9	5.036 AU	4.676 AU	15h11m	-04°06'	105.0°	11.2°	110°

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. (6.5 + 5 log[∆] + 20.0 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 121P/Shoemaker-Holt are:

    e (Eccentricity)                : 0.1865290
    q (Perihelion distance)         : 3.7357580
    i (Inclination)                 : 20.16100
    Ω (Longitude of ascending node) : 94.10800
    ω (Argument of perihelion)      : 12.16240
    L (Longitude of perihelion)     : 105.54544
    B (Latitude of perihelion)      : 4.16414
    T (Time of perihelion passage)  : 2460127.27230
    P (Orbital period in years)     : 9.84

    Epoch                           : 2026 Jul 23
    Reference                       : MPEC 2026-K60

    Classification(s):              : Ecliptic; Jupiter family
    Tisserand (Jupiter)             : 2.866

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-07-23 00:00 UT   15 10 59.0   -04 01 02     4.656    5.034  106.2   11.2   110   23.9 
2026-07-24 00:00 UT   15 11 01.6   -04 05 22     4.672    5.035  105.3   11.2   110   23.9 
2026-07-24 06:08 UT   15 11 02.3   -04 06 29     4.676    5.036  105.0   11.2   110   23.9 
2026-07-25 00:00 UT   15 11 04.9   -04 09 45     4.687    5.036  104.4   11.3   109   23.9 
2026-07-26 00:00 UT   15 11 08.9   -04 14 10     4.703    5.038  103.5   11.3   109   23.9 
2026-07-27 00:00 UT   15 11 13.8   -04 18 38     4.719    5.039  102.6   11.3   109   23.9 
2026-07-28 00:00 UT   15 11 19.3   -04 23 07     4.735    5.040  101.7   11.4   109   23.9 
2026-07-29 00:00 UT   15 11 25.6   -04 27 38     4.751    5.041  100.8   11.4   108   23.9 
2026-07-30 00:00 UT   15 11 32.5   -04 32 12     4.767    5.042  100.0   11.4   108   23.9 
2026-07-31 00:00 UT   15 11 40.2   -04 36 47     4.783    5.043   99.1   11.5   108   24.0 
2026-08-01 00:00 UT   15 11 48.7   -04 41 24     4.799    5.045   98.2   11.5   108   24.0 
2026-08-02 00:00 UT   15 11 57.8   -04 46 03     4.815    5.046   97.3   11.5   107   24.0 
2026-08-03 00:00 UT   15 12 07.6   -04 50 44     4.831    5.047   96.5   11.5   107   24.0 

    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.