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C/2013 A1 (Siding Spring)
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach6 Sep 20149.21.577 AU0.906 AU 21h37m-74°42'110.8°36.7°22°
Perihelion27 Oct 201410.31.393 AU1.770 AU 17h40m-21°47'51.7°34.1°91°
Today12 Apr 202624.027.257 AU26.884 AU 09h32m+34°04'110.8°2.0°117°
C/2013 A1 (Siding Spring)- 2026-04-12
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. (8.2 + 5 log[∆] + 6.0 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/2013 A1 (Siding Spring) are: 

    e (Eccentricity)                : 1.0001520
    q (Perihelion distance)         : 1.3929680
    i (Inclination)                 : 128.68580
    Ω (Longitude of ascending node) : 301.18470
    ω (Argument of perihelion)      : 2.56140
    L (Longitude of perihelion)     : 299.58305
    B (Latitude of perihelion)      : 1.99913
    T (Time of perihelion passage)  : 2456958.03950

    Epoch                           : 2026 Apr 11
    Reference                       : MPEC 2026-E44

    Classification(s):              : Nearly isotropic; New (a > 10000 AU)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-04-11 00:00 UT   09 33 04.4   +34 04 38    26.852   27.250  112.4    1.9   118   24.0 
2026-04-12 00:00 UT   09 32 58.8   +34 04 16    26.871   27.254  111.4    2.0   117   24.0 
2026-04-12 15:15 UT   09 32 55.3   +34 04 01    26.884   27.257  110.8    2.0   117   24.0 
2026-04-13 00:00 UT   09 32 53.4   +34 03 52    26.891   27.259  110.5    2.0   117   24.0 
2026-04-14 00:00 UT   09 32 48.1   +34 03 28    26.911   27.264  109.6    2.0   116   24.0 
2026-04-15 00:00 UT   09 32 43.0   +34 03 03    26.930   27.268  108.6    2.0   116   24.0 
2026-04-16 00:00 UT   09 32 38.0   +34 02 37    26.950   27.273  107.7    2.0   116   24.0 
2026-04-17 00:00 UT   09 32 33.2   +34 02 10    26.970   27.277  106.8    2.0   115   24.0 
2026-04-18 00:00 UT   09 32 28.6   +34 01 42    26.990   27.282  105.8    2.0   115   24.0 
2026-04-19 00:00 UT   09 32 24.2   +34 01 13    27.010   27.286  104.9    2.0   115   24.0 
2026-04-20 00:00 UT   09 32 19.9   +34 00 44    27.030   27.291  104.0    2.0   114   24.0 
2026-04-21 00:00 UT   09 32 15.8   +34 00 13    27.051   27.295  103.0    2.1   114   24.0 
2026-04-22 00:00 UT   09 32 11.8   +33 59 42    27.071   27.300  102.1    2.1   114   24.0 




    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.

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