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	18 Sep 2025	29.7	20.823 AU	21.745 AU	13h12m	-01°10'	22.8°	1.1°	98°

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 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)
        

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 (11.00 + 5 log[∆] + 10.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 9.86 + 5 log[∆] + 10.00 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
2025-09-18 00:00 UT   13 12 21.9   -01 10 47    21.743   20.822   22.9    1.1    98   29.7 
2025-09-18 02:39 UT   13 12 22.9   -01 10 55    21.745   20.823   22.8    1.1    98   29.7 
2025-09-19 00:00 UT   13 12 31.6   -01 12 02    21.755   20.827   22.0    1.0    97   29.7 
2025-09-20 00:00 UT   13 12 41.3   -01 13 17    21.765   20.832   21.1    1.0    97   29.7 
2025-09-21 00:00 UT   13 12 51.1   -01 14 33    21.776   20.837   20.2    1.0    96   29.7 
2025-09-22 00:00 UT   13 13 01.0   -01 15 48    21.786   20.842   19.3    0.9    95   29.7 
2025-09-23 00:00 UT   13 13 10.9   -01 17 04    21.796   20.847   18.5    0.9    94   29.7 
2025-09-24 00:00 UT   13 13 20.9   -01 18 19    21.806   20.852   17.6    0.8    93   29.7 
2025-09-25 00:00 UT   13 13 30.9   -01 19 35    21.816   20.857   16.7    0.8    92   29.7 
2025-09-26 00:00 UT   13 13 41.0   -01 20 50    21.825   20.863   15.8    0.8    91   29.7 
2025-09-27 00:00 UT   13 13 51.1   -01 22 05    21.834   20.868   15.0    0.7    89   29.8 
2025-09-28 00:00 UT   13 14 01.2   -01 23 20    21.842   20.873   14.1    0.7    88   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.