38P/Stephan-Oterma
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	14 Nov 2018	10.1	1.582 AU	0.820 AU	07h24m	+21°46'	121.7°	32.2°	278°
Nearest approach	15 Dec 2018	10.1	1.633 AU	0.732 AU	08h10m	+34°49'	143.8°	20.9°	262°
Today	20 Jul 2026	30.5	15.666 AU	15.156 AU	15h40m	-13°10'	118.4°	3.3°	107°

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 7.8 + 5 log[∆] + 14.1 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 38P/Stephan-Oterma are:

    e (Eccentricity)                : 0.8596170
    q (Perihelion distance)         : 1.5824950
    i (Inclination)                 : 18.40650
    Ω (Longitude of ascending node) : 77.87060
    ω (Argument of perihelion)      : 359.61950
    L (Longitude of perihelion)     : 77.50957
    B (Latitude of perihelion)      : -0.12014
    T (Time of perihelion passage)  : 2458436.52630
    P (Orbital period in years)     : 37.85

    Epoch                           : 2026 Mar 16
    Reference                       : MPC191595

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-07-19 00:00 UT   15 40 55.5   -13 09 54    15.131   15.661  119.8    3.2   107   30.5 
2026-07-20 00:00 UT   15 40 49.3   -13 10 03    15.148   15.664  118.9    3.3   107   30.5 
2026-07-20 11:05 UT   15 40 46.5   -13 10 08    15.156   15.666  118.4    3.3   107   30.5 
2026-07-21 00:00 UT   15 40 43.3   -13 10 13    15.166   15.667  117.9    3.3   107   30.5 
2026-07-22 00:00 UT   15 40 37.6   -13 10 24    15.183   15.670  116.9    3.3   106   30.5 
2026-07-23 00:00 UT   15 40 32.1   -13 10 36    15.201   15.673  116.0    3.3   106   30.5 
2026-07-24 00:00 UT   15 40 26.8   -13 10 49    15.219   15.676  115.0    3.4   106   30.5 
2026-07-25 00:00 UT   15 40 21.8   -13 11 03    15.237   15.678  114.0    3.4   106   30.5 
2026-07-26 00:00 UT   15 40 17.1   -13 11 18    15.255   15.681  113.1    3.4   106   30.5 
2026-07-27 00:00 UT   15 40 12.5   -13 11 34    15.274   15.684  112.1    3.4   106   30.5 
2026-07-28 00:00 UT   15 40 08.3   -13 11 50    15.292   15.687  111.1    3.5   106   30.5 
2026-07-29 00:00 UT   15 40 04.3   -13 12 08    15.310   15.690  110.2    3.5   106   30.5 
2026-07-30 00:00 UT   15 40 00.5   -13 12 26    15.329   15.692  109.2    3.5   105   30.5 

    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.