C/2017 A3 (Elenin)
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach24 Jan 201718.03.841 AU3.412 AU 06h18m-46°04'108.6°14.1°32°
Perihelion31 Jan 201718.03.840 AU3.417 AU 06h10m-43°51'108.2°14.1°41°
Today21 Oct 202528.719.210 AU19.021 AU 19h20m+79°02'99.5°2.9°82°
C/2017 A3 (Elenin)- 2025-10-21
astro.vanbuitenen.nl


 
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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)                : 0.9113940
    q (Perihelion distance)         : 3.8404320
    i (Inclination)                 : 98.50290
    Ω (Longitude of ascending node) : 97.85120
    ω (Argument of perihelion)      : 303.92640
    L (Longitude of perihelion)     : 110.24874
    B (Latitude of perihelion)      : -55.14840
    T (Time of perihelion passage)  : 2457784.51680
    P (Orbital period in years)     : 285.35

    Epoch                           : 2022 Mar 31
    Reference                       : MPC108594

    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
2025-10-20 00:00 UT   19 20 43.6   +79 08 00    19.019   19.204   99.2    2.9    84   28.7 
2025-10-21 00:00 UT   19 20 53.3   +79 04 33    19.020   19.208   99.4    2.9    83   28.7 
2025-10-21 11:31 UT   19 20 58.3   +79 02 53    19.021   19.210   99.5    2.9    82   28.7 
2025-10-22 00:00 UT   19 21 04.0   +79 01 05    19.022   19.212   99.6    2.9    82   28.7 
2025-10-23 00:00 UT   19 21 15.7   +78 57 38    19.023   19.217   99.7    2.9    81   28.7 
2025-10-24 00:00 UT   19 21 28.4   +78 54 12    19.025   19.221   99.9    2.9    80   28.7 
2025-10-25 00:00 UT   19 21 42.0   +78 50 46    19.026   19.225  100.0    2.9    79   28.7 
2025-10-26 00:00 UT   19 21 56.6   +78 47 21    19.028   19.229  100.2    2.9    78   28.7 
2025-10-27 00:00 UT   19 22 12.1   +78 43 56    19.030   19.234  100.4    2.9    77   28.7 
2025-10-28 00:00 UT   19 22 28.5   +78 40 32    19.032   19.238  100.5    2.9    76   28.7 
2025-10-29 00:00 UT   19 22 45.8   +78 37 09    19.033   19.242  100.6    2.9    75   28.7 
2025-10-30 00:00 UT   19 23 03.9   +78 33 47    19.035   19.246  100.8    2.9    74   28.7 
2025-10-31 00:00 UT   19 23 22.9   +78 30 25    19.037   19.251  100.9    2.9    73   28.7 



    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.