C/2017 A3 (Elenin)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	23 Jan 2017	18.0	3.864 AU	3.425 AU	06h19m	-45°26'	109.4°	13.9°	31°
Perihelion	27 Jan 2017	18.0	3.864 AU	3.426 AU	06h14m	-44°11'	109.2°	13.9°	36°
Today	9 Apr 2026	29.0	19.925 AU	20.133 AU	21h01m	+77°02'	76.6°	2.8°	295°

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. The light curve is based on the absolute magnitude and slope parameter as calculated from an MPEC, or the latest values provided by the minor planet center. (9.5 + 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 A3 (Elenin) are:

    e (Eccentricity)                : 0.9107720
    q (Perihelion distance)         : 3.8640750
    i (Inclination)                 : 98.43470
    Ω (Longitude of ascending node) : 97.67030
    ω (Argument of perihelion)      : 304.05950
    L (Longitude of perihelion)     : 109.91250
    B (Latitude of perihelion)      : -55.03433
    T (Time of perihelion passage)  : 2457780.87610
    P (Orbital period in years)     : 284.98

    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
2026-04-08 00:00 UT   21 01 02.3   +76 58 53    20.120   19.918   76.9    2.8   297   29.0 
2026-04-09 00:00 UT   21 01 19.2   +77 01 11    20.127   19.922   76.7    2.8   296   29.0 
2026-04-09 17:55 UT   21 01 31.3   +77 02 55    20.133   19.925   76.6    2.8   295   29.0 
2026-04-10 00:00 UT   21 01 35.4   +77 03 30    20.134   19.926   76.6    2.8   295   29.0 
2026-04-11 00:00 UT   21 01 50.8   +77 05 51    20.142   19.930   76.4    2.8   294   29.0 
2026-04-12 00:00 UT   21 02 05.6   +77 08 13    20.149   19.934   76.2    2.8   293   29.0 
2026-04-13 00:00 UT   21 02 19.7   +77 10 35    20.156   19.938   76.1    2.8   292   29.0 
2026-04-14 00:00 UT   21 02 33.0   +77 12 59    20.163   19.943   75.9    2.8   291   29.0 
2026-04-15 00:00 UT   21 02 45.5   +77 15 23    20.170   19.947   75.7    2.8   290   29.0 
2026-04-16 00:00 UT   21 02 57.3   +77 17 49    20.177   19.951   75.6    2.8   289   29.0 
2026-04-17 00:00 UT   21 03 08.3   +77 20 15    20.183   19.955   75.4    2.8   288   29.0 
2026-04-18 00:00 UT   21 03 18.6   +77 22 42    20.190   19.959   75.3    2.8   287   29.0 
2026-04-19 00:00 UT   21 03 28.0   +77 25 10    20.197   19.963   75.1    2.8   287   29.0 

    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.