38P/Stephan-Oterma
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	13 Nov 2018	6.8	1.580 AU	0.819 AU	07h25m	+21°44'	121.4°	32.3°	278°
Nearest approach	15 Dec 2018	6.9	1.631 AU	0.731 AU	08h11m	+34°49'	143.5°	21.1°	263°
Today	18 Jul 2025	41.9	14.562 AU	14.077 AU	15h30m	-11°40'	116.7°	3.6°	108°

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.)

The orbital elements of 38P/Stephan-Oterma are:

            e (Eccentricity)                : 0.8597680
            q (Perihelion distance)         : 1.5797830
            i (Inclination)                 : 18.41410
            Ω (Longitude of ascending node) : 77.86140
            ω (Argument of perihelion)      : 359.59460
            L (Longitude of perihelion)     : 77.47676
            B (Latitude of perihelion)      : -0.12806
            T (Time of perihelion passage)  : 2458436.39550
            P (Orbital period in years)     : 37.81

            Epoch                           : 2025 Jul 17
            Reference                       : MPEC 2024-YC7

            Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); Halley type (P < 200 years)
        

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. The gray curve is based on the absolute magnitude and slope parameter as calculated from the original MPEC, or the latest values provided by the MPC (3.50 + 5 log[∆] + 30.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 1.26 + 5 log[∆] + 30.00 log[r]).

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-07-18 00:00 UT   15 30 09.0   -11 39 57    14.060   14.559  117.6    3.5   108   41.9 
2025-07-18 22:56 UT   15 30 03.2   -11 40 11    14.077   14.562  116.7    3.6   108   41.9 
2025-07-19 00:00 UT   15 30 03.0   -11 40 12    14.078   14.562  116.6    3.6   108   41.9 
2025-07-20 00:00 UT   15 29 57.2   -11 40 28    14.096   14.565  115.7    3.6   108   41.9 
2025-07-21 00:00 UT   15 29 51.7   -11 40 45    14.115   14.568  114.7    3.6   107   41.9 
2025-07-22 00:00 UT   15 29 46.5   -11 41 03    14.133   14.572  113.7    3.7   107   41.9 
2025-07-23 00:00 UT   15 29 41.5   -11 41 23    14.151   14.575  112.8    3.7   107   41.9 
2025-07-24 00:00 UT   15 29 36.8   -11 41 43    14.170   14.578  111.8    3.7   107   41.9 
2025-07-25 00:00 UT   15 29 32.4   -11 42 05    14.189   14.581  110.8    3.7   107   41.9 
2025-07-26 00:00 UT   15 29 28.2   -11 42 27    14.208   14.584  109.9    3.8   107   41.9 
2025-07-27 00:00 UT   15 29 24.3   -11 42 51    14.227   14.588  108.9    3.8   107   41.9 
2025-07-28 00:00 UT   15 29 20.7   -11 43 15    14.246   14.591  107.9    3.8   106   41.9 

    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.