38P/Stephan-Oterma
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	14 Nov 2018	6.8	1.581 AU	0.819 AU	07h25m	+21°45'	121.6°	32.2°	278°
Nearest approach	15 Dec 2018	7.0	1.632 AU	0.731 AU	08h10m	+34°48'	143.7°	20.9°	262°
Today	24 Dec 2025	42.6	15.056 AU	15.870 AU	15h56m	-14°05'	33.2°	2.0°	291°

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 1.3 + 5 log[∆] + 30.0 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 38P/Stephan-Oterma are:

    e (Eccentricity)                : 0.8596770
    q (Perihelion distance)         : 1.5814990
    i (Inclination)                 : 18.40980
    Ω (Longitude of ascending node) : 77.86670
    ω (Argument of perihelion)      : 359.61200
    L (Longitude of perihelion)     : 77.49856
    B (Latitude of perihelion)      : -0.12253
    T (Time of perihelion passage)  : 2458436.51890
    P (Orbital period in years)     : 37.84

    Epoch                           : 2025 Dec 23
    Reference                       : MPEC 2025-W75

    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
2025-12-23 00:00 UT   15 55 51.0   -14 05 01    15.879   15.052   31.8    2.0   292   42.6 
2025-12-24 00:00 UT   15 56 05.6   -14 05 40    15.873   15.055   32.7    2.0   292   42.6 
2025-12-24 12:12 UT   15 56 13.0   -14 05 60    15.870   15.056   33.2    2.0   291   42.6 
2025-12-25 00:00 UT   15 56 20.1   -14 06 18    15.867   15.058   33.7    2.1   291   42.6 
2025-12-26 00:00 UT   15 56 34.4   -14 06 56    15.860   15.061   34.6    2.1   291   42.6 
2025-12-27 00:00 UT   15 56 48.6   -14 07 33    15.853   15.064   35.5    2.2   291   42.6 
2025-12-28 00:00 UT   15 57 02.7   -14 08 08    15.846   15.067   36.5    2.2   290   42.6 
2025-12-29 00:00 UT   15 57 16.6   -14 08 43    15.839   15.070   37.4    2.3   290   42.6 
2025-12-30 00:00 UT   15 57 30.4   -14 09 17    15.831   15.073   38.4    2.3   290   42.6 
2025-12-31 00:00 UT   15 57 44.0   -14 09 51    15.824   15.076   39.3    2.4   289   42.6 
2026-01-01 00:00 UT   15 57 57.5   -14 10 23    15.816   15.079   40.3    2.4   289   42.6 
2026-01-02 00:00 UT   15 58 10.8   -14 10 55    15.808   15.082   41.2    2.5   289   42.6 
2026-01-03 00:00 UT   15 58 24.0   -14 11 25    15.799   15.085   42.2    2.5   289   42.6 

    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.