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	4 Nov 2026	30.3	22.871 AU	23.788 AU	13h22m	-03°09'	21.9°	0.9°	305°

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
2026-11-03 00:00 UT   13 22 17.7   -03 08 19    23.790   22.865   20.6    0.9   306   30.3 
2026-11-04 00:00 UT   13 22 26.8   -03 09 17    23.789   22.870   21.6    0.9   305   30.3 
2026-11-04 09:17 UT   13 22 30.3   -03 09 39    23.788   22.871   21.9    0.9   305   30.3 
2026-11-05 00:00 UT   13 22 35.9   -03 10 14    23.787   22.874   22.5    1.0   304   30.3 
2026-11-06 00:00 UT   13 22 44.9   -03 11 10    23.785   22.879   23.4    1.0   304   30.3 
2026-11-07 00:00 UT   13 22 53.9   -03 12 06    23.783   22.884   24.4    1.0   303   30.3 
2026-11-08 00:00 UT   13 23 02.8   -03 13 01    23.780   22.889   25.3    1.1   303   30.3 
2026-11-09 00:00 UT   13 23 11.6   -03 13 55    23.777   22.894   26.3    1.1   302   30.3 
2026-11-10 00:00 UT   13 23 20.4   -03 14 49    23.774   22.899   27.2    1.1   302   30.3 
2026-11-11 00:00 UT   13 23 29.1   -03 15 42    23.771   22.904   28.2    1.2   302   30.3 
2026-11-12 00:00 UT   13 23 37.8   -03 16 35    23.768   22.908   29.1    1.2   301   30.3 
2026-11-13 00:00 UT   13 23 46.3   -03 17 27    23.764   22.913   30.1    1.2   301   30.3 
2026-11-14 00:00 UT   13 23 54.8   -03 18 18    23.760   22.918   31.0    1.3   300   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.