C/2017 O1 (ASASSN)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	16 Oct 2017	10.8	1.491 AU	0.697 AU	04h33m	+51°36'	122.3°	34.4°	240°
Nearest approach	17 Oct 2017	10.8	1.491 AU	0.696 AU	04h35m	+53°25'	122.4°	34.3°	238°
Today	9 Nov 2025	29.8	21.087 AU	21.956 AU	13h21m	-02°11'	27.9°	1.3°	303°

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 9.9 + 5 log[∆] + 10.0 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 C/2017 O1 (ASASSN) are:

    e (Eccentricity)                : 0.9961060
    q (Perihelion distance)         : 1.4906670
    i (Inclination)                 : 39.99240
    Ω (Longitude of ascending node) : 25.71300
    ω (Argument of perihelion)      : 20.84740
    L (Longitude of perihelion)     : 41.97765
    B (Latitude of perihelion)      : 13.22168
    T (Time of perihelion passage)  : 2458042.56890
    P (Orbital period in years)     : 7489.92

    Epoch                           : 2022 Nov 15
    Reference                       : MPEC 2022-OB6

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-11-08 00:00 UT   13 21 00.1   -02 10 31    21.960   21.079   26.6    1.2   304   29.8 
2025-11-09 00:00 UT   13 21 09.7   -02 11 29    21.958   21.084   27.5    1.2   303   29.8 
2025-11-09 10:40 UT   13 21 13.9   -02 11 55    21.956   21.087   27.9    1.3   303   29.8 
2025-11-10 00:00 UT   13 21 19.1   -02 12 27    21.954   21.090   28.4    1.3   303   29.8 
2025-11-11 00:00 UT   13 21 28.5   -02 13 24    21.951   21.095   29.4    1.3   303   29.8 
2025-11-12 00:00 UT   13 21 37.8   -02 14 20    21.947   21.100   30.3    1.4   302   29.8 
2025-11-13 00:00 UT   13 21 47.0   -02 15 15    21.944   21.105   31.3    1.4   302   29.8 
2025-11-14 00:00 UT   13 21 56.2   -02 16 10    21.940   21.110   32.2    1.4   301   29.8 
2025-11-15 00:00 UT   13 22 05.2   -02 17 04    21.935   21.115   33.2    1.5   301   29.8 
2025-11-16 00:00 UT   13 22 14.2   -02 17 57    21.931   21.120   34.1    1.5   301   29.8 
2025-11-17 00:00 UT   13 22 23.1   -02 18 50    21.926   21.125   35.1    1.5   300   29.8 
2025-11-18 00:00 UT   13 22 31.9   -02 19 41    21.921   21.130   36.0    1.6   300   29.8 
2025-11-19 00:00 UT   13 22 40.6   -02 20 32    21.915   21.135   37.0    1.6   300   29.8 

    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.