C/2017 O1 (ASASSN)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	16 Oct 2017	10.9	1.505 AU	0.706 AU	04h30m	+51°29'	123.2°	33.7°	238°
Nearest approach	18 Oct 2017	10.9	1.505 AU	0.706 AU	04h31m	+53°33'	123.4°	33.6°	236°
Today	6 Sep 2026	30.2	22.583 AU	23.401 AU	13h13m	-02°05'	35.0°	1.5°	105°

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)                : 0.9966450
    q (Perihelion distance)         : 1.5045250
    i (Inclination)                 : 39.81820
    Ω (Longitude of ascending node) : 25.76200
    ω (Argument of perihelion)      : 21.01540
    L (Longitude of perihelion)     : 42.20202
    B (Latitude of perihelion)      : 13.27605
    T (Time of perihelion passage)  : 2458043.00570
    P (Orbital period in years)     : 9496.43

    Epoch                           : 2026 May 29
    Reference                       : MPC194152

    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
2026-09-05 00:00 UT   13 13 16.0   -02 04 04    23.386   22.578   35.9    1.5   105   30.2 
2026-09-06 00:00 UT   13 13 23.9   -02 05 09    23.400   22.583   35.0    1.5   105   30.2 
2026-09-06 01:00 UT   13 13 24.2   -02 05 11    23.401   22.583   35.0    1.5   105   30.2 
2026-09-07 00:00 UT   13 13 31.9   -02 06 14    23.414   22.587   34.1    1.4   104   30.2 
2026-09-08 00:00 UT   13 13 40.0   -02 07 19    23.428   22.592   33.2    1.4   104   30.2 
2026-09-09 00:00 UT   13 13 48.2   -02 08 25    23.442   22.597   32.2    1.4   104   30.3 
2026-09-10 00:00 UT   13 13 56.4   -02 09 31    23.456   22.602   31.3    1.3   104   30.3 
2026-09-11 00:00 UT   13 14 04.7   -02 10 37    23.469   22.607   30.4    1.3   103   30.3 
2026-09-12 00:00 UT   13 14 13.1   -02 11 44    23.482   22.612   29.5    1.3   103   30.3 
2026-09-13 00:00 UT   13 14 21.6   -02 12 50    23.495   22.617   28.6    1.2   103   30.3 
2026-09-14 00:00 UT   13 14 30.2   -02 13 57    23.507   22.622   27.7    1.2   102   30.3 
2026-09-15 00:00 UT   13 14 38.8   -02 15 04    23.520   22.627   26.7    1.1   102   30.3 
2026-09-16 00:00 UT   13 14 47.5   -02 16 11    23.532   22.631   25.8    1.1   101   30.3 

    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.