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	8 Jan 2026	29.8	21.390 AU	21.416 AU	13h27m	-02°42'	87.1°	2.6°	292°

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
2026-01-07 00:00 UT   13 27 09.4   -02 42 02    21.440   21.380   85.2    2.6   292   29.8 
2026-01-08 00:00 UT   13 27 11.0   -02 42 02    21.427   21.385   86.2    2.6   292   29.8 
2026-01-08 21:25 UT   13 27 12.2   -02 42 00    21.416   21.390   87.1    2.6   292   29.8 
2026-01-09 00:00 UT   13 27 12.3   -02 41 60    21.415   21.390   87.2    2.6   292   29.8 
2026-01-10 00:00 UT   13 27 13.5   -02 41 57    21.403   21.395   88.2    2.6   292   29.8 
2026-01-11 00:00 UT   13 27 14.4   -02 41 53    21.390   21.400   89.2    2.6   292   29.8 
2026-01-12 00:00 UT   13 27 15.2   -02 41 48    21.378   21.405   90.2    2.6   292   29.8 
2026-01-13 00:00 UT   13 27 15.9   -02 41 42    21.366   21.410   91.2    2.6   292   29.8 
2026-01-14 00:00 UT   13 27 16.3   -02 41 35    21.353   21.415   92.3    2.6   292   29.8 
2026-01-15 00:00 UT   13 27 16.5   -02 41 27    21.341   21.420   93.3    2.6   291   29.8 
2026-01-16 00:00 UT   13 27 16.6   -02 41 18    21.329   21.425   94.3    2.6   291   29.8 
2026-01-17 00:00 UT   13 27 16.5   -02 41 07    21.316   21.430   95.3    2.6   291   29.8 
2026-01-18 00:00 UT   13 27 16.2   -02 40 56    21.304   21.435   96.3    2.6   291   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.