C/2017 O1 (ASASSN)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	16 Oct 2017	10.9	1.503 AU	0.703 AU	04h29m	+51°36'	123.5°	33.6°	238°
Nearest approach	18 Oct 2017	10.9	1.503 AU	0.702 AU	04h29m	+53°25'	123.6°	33.5°	236°
Today	20 Apr 2026	29.9	21.903 AU	20.924 AU	13h16m	-01°34'	166.6°	0.6°	139°

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)                : 0.9966460
    q (Perihelion distance)         : 1.5031850
    i (Inclination)                 : 39.83930
    Ω (Longitude of ascending node) : 25.75680
    ω (Argument of perihelion)      : 21.00550
    L (Longitude of perihelion)     : 42.18402
    B (Latitude of perihelion)      : 13.27594
    T (Time of perihelion passage)  : 2458043.22760
    P (Orbital period in years)     : 9487.99

    Epoch                           : 2026 Mar 16
    Reference                       : MPEC 2026-E44

    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
2026-04-19 00:00 UT   13 16 50.3   -01 36 15    20.910   21.895  168.1    0.5   142   29.9 
2026-04-20 00:00 UT   13 16 40.3   -01 35 27    20.918   21.899  167.2    0.6   140   29.9 
2026-04-20 16:44 UT   13 16 33.4   -01 34 54    20.924   21.903  166.6    0.6   139   29.9 
2026-04-21 00:00 UT   13 16 30.5   -01 34 40    20.926   21.904  166.3    0.6   138   29.9 
2026-04-22 00:00 UT   13 16 20.6   -01 33 53    20.935   21.909  165.4    0.7   136   29.9 
2026-04-23 00:00 UT   13 16 10.8   -01 33 07    20.943   21.914  164.5    0.7   135   29.9 
2026-04-24 00:00 UT   13 16 01.1   -01 32 21    20.952   21.919  163.5    0.7   133   29.9 
2026-04-25 00:00 UT   13 15 51.4   -01 31 36    20.962   21.924  162.6    0.8   132   29.9 
2026-04-26 00:00 UT   13 15 41.7   -01 30 52    20.971   21.929  161.6    0.8   131   29.9 
2026-04-27 00:00 UT   13 15 32.1   -01 30 08    20.981   21.934  160.7    0.9   130   29.9 
2026-04-28 00:00 UT   13 15 22.6   -01 29 25    20.991   21.939  159.7    0.9   129   29.9 
2026-04-29 00:00 UT   13 15 13.1   -01 28 42    21.002   21.944  158.8    1.0   128   29.9 
2026-04-30 00:00 UT   13 15 03.7   -01 28 00    21.013   21.949  157.8    1.0   127   29.9 

    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.