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 Jan 2026	29.8	21.438 AU	21.297 AU	13h27m	-02°40'	96.9°	2.6°	291°

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
2026-01-17 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 
2026-01-18 13:22 UT   13 27 15.9   -02 40 49    21.297   21.438   96.9    2.6   291   29.8 
2026-01-19 00:00 UT   13 27 15.7   -02 40 43    21.292   21.440   97.3    2.6   291   29.8 
2026-01-20 00:00 UT   13 27 15.0   -02 40 29    21.280   21.445   98.4    2.6   291   29.8 
2026-01-21 00:00 UT   13 27 14.2   -02 40 15    21.267   21.450   99.4    2.6   291   29.8 
2026-01-22 00:00 UT   13 27 13.1   -02 39 59    21.255   21.455  100.4    2.6   291   29.8 
2026-01-23 00:00 UT   13 27 11.9   -02 39 42    21.243   21.460  101.4    2.6   291   29.8 
2026-01-24 00:00 UT   13 27 10.5   -02 39 24    21.231   21.465  102.4    2.6   290   29.8 
2026-01-25 00:00 UT   13 27 08.9   -02 39 05    21.219   21.470  103.4    2.6   290   29.8 
2026-01-26 00:00 UT   13 27 07.1   -02 38 45    21.208   21.475  104.5    2.5   290   29.8 
2026-01-27 00:00 UT   13 27 05.2   -02 38 24    21.196   21.480  105.5    2.5   290   29.8 
2026-01-28 00:00 UT   13 27 03.0   -02 38 02    21.184   21.485  106.5    2.5   290   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.