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C/2013 A1 (Siding Spring)
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach4 Sep 20149.11.583 AU0.889 AU21h34m-73°18'113.0°35.9°21°
Perihelion24 Oct 201410.31.411 AU1.745 AU17h36m-21°44'53.9°34.7°91°
Today17 Oct 202523.926.430 AU26.812 AU09h51m+32°25'66.4°2.0°299°
C/2013 A1 (Siding Spring)- 2025-10-17
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)                : 0.9998840
    q (Perihelion distance)         : 1.4113330
    i (Inclination)                 : 129.15450
    Ω (Longitude of ascending node) : 300.88820
    ω (Argument of perihelion)      : 2.53870
    L (Longitude of perihelion)     : 299.28460
    B (Latitude of perihelion)      : 1.96837
    T (Time of perihelion passage)  : 2456954.82720

    Epoch                           : 2020 Sep 26
    Reference                       : MPC103843

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-10-16 00:00 UT   09 51 07.2   +32 24 51    26.826   26.424   65.2    2.0   300   23.9 
2025-10-17 00:00 UT   09 51 11.7   +32 25 04    26.816   26.428   66.1    2.0   299   23.9 
2025-10-17 08:22 UT   09 51 13.2   +32 25 08    26.812   26.430   66.4    2.0   299   23.9 
2025-10-18 00:00 UT   09 51 16.1   +32 25 17    26.805   26.433   67.0    2.0   299   23.9 
2025-10-19 00:00 UT   09 51 20.3   +32 25 31    26.795   26.437   67.9    2.0   298   23.9 
2025-10-20 00:00 UT   09 51 24.3   +32 25 47    26.784   26.442   68.9    2.0   298   23.9 
2025-10-21 00:00 UT   09 51 28.3   +32 26 03    26.773   26.447   69.8    2.0   298   23.9 
2025-10-22 00:00 UT   09 51 32.0   +32 26 21    26.762   26.451   70.7    2.0   297   23.9 
2025-10-23 00:00 UT   09 51 35.6   +32 26 39    26.751   26.456   71.7    2.0   297   23.9 
2025-10-24 00:00 UT   09 51 39.1   +32 26 58    26.740   26.460   72.6    2.1   297   23.9 
2025-10-25 00:00 UT   09 51 42.4   +32 27 19    26.729   26.465   73.5    2.1   296   23.9 
2025-10-26 00:00 UT   09 51 45.6   +32 27 40    26.718   26.470   74.5    2.1   296   23.9 
2025-10-27 00:00 UT   09 51 48.6   +32 28 03    26.707   26.474   75.4    2.1   296   23.9 




    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.

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