38P/Stephan-Oterma
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	13 Nov 2018	6.8	1.579 AU	0.820 AU	07h25m	+21°43'	121.3°	32.4°	279°
Nearest approach	15 Dec 2018	6.9	1.631 AU	0.731 AU	08h12m	+34°49'	143.4°	21.1°	263°
Today	9 May 2025	41.6	14.333 AU	13.340 AU	15h44m	-12°03'	168.9°	0.8°	240°

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)                : 0.8597840
            q (Perihelion distance)         : 1.5793310
            i (Inclination)                 : 18.41470
            Ω (Longitude of ascending node) : 77.86050
            ω (Argument of perihelion)      : 359.58810
            L (Longitude of perihelion)     : 77.46969
            B (Latitude of perihelion)      : -0.13012
            T (Time of perihelion passage)  : 2458436.30790
            P (Orbital period in years)     : 37.80

            Epoch                           : 2025 May 08
            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
2025-05-09 00:00 UT   15 44 49.9   -12 04 08    13.340   14.332  168.7    0.8   241   41.6 
2025-05-09 07:27 UT   15 44 45.2   -12 03 54    13.340   14.333  168.9    0.8   240   41.6 
2025-05-10 00:00 UT   15 44 34.5   -12 03 21    13.341   14.335  169.4    0.7   238   41.6 
2025-05-11 00:00 UT   15 44 19.1   -12 02 35    13.342   14.338  170.1    0.7   233   41.6 
2025-05-12 00:00 UT   15 44 03.7   -12 01 48    13.343   14.341  170.8    0.6   228   41.6 
2025-05-13 00:00 UT   15 43 48.2   -12 01 03    13.345   14.345  171.3    0.6   223   41.6 
2025-05-14 00:00 UT   15 43 32.6   -12 00 17    13.347   14.348  171.8    0.6   217   41.6 
2025-05-15 00:00 UT   15 43 17.1   -11 59 33    13.349   14.351  172.1    0.6   210   41.6 
2025-05-16 00:00 UT   15 43 01.6   -11 58 48    13.352   14.355  172.4    0.5   202   41.6 
2025-05-17 00:00 UT   15 42 46.0   -11 58 05    13.355   14.358  172.5    0.5   195   41.6 
2025-05-18 00:00 UT   15 42 30.4   -11 57 21    13.358   14.361  172.4    0.5   187   41.6 
2025-05-19 00:00 UT   15 42 14.9   -11 56 38    13.361   14.364  172.2    0.5   179   41.6 

    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.