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C/2013 A1 (Siding Spring)
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach5 Sep 20149.21.581 AU0.903 AU 21h37m-74°08'111.6°36.3°21°
Perihelion26 Oct 201410.31.402 AU1.765 AU 17h39m-21°46'52.5°34.2°91°
Today13 Nov 202523.926.567 AU26.509 AU 09h52m+32°36'92.3°2.1°290°
C/2013 A1 (Siding Spring)- 2025-11-13
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)                : 1.0001170
    q (Perihelion distance)         : 1.4017490
    i (Inclination)                 : 128.76610
    Ω (Longitude of ascending node) : 301.19590
    ω (Argument of perihelion)      : 2.57270
    L (Longitude of perihelion)     : 299.58436
    B (Latitude of perihelion)      : 2.00569
    T (Time of perihelion passage)  : 2456957.11860

    Epoch                           : 2025 Nov 13
    Reference                       : MPC103843

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-11-12 00:00 UT   09 52 44.9   +32 35 25    26.532   26.559   90.4    2.1   291   23.9 
2025-11-13 00:00 UT   09 52 45.2   +32 36 03    26.520   26.563   91.4    2.1   290   23.9 
2025-11-13 21:25 UT   09 52 45.2   +32 36 38    26.509   26.567   92.3    2.1   290   23.9 
2025-11-14 00:00 UT   09 52 45.2   +32 36 42    26.508   26.568   92.4    2.1   290   23.9 
2025-11-15 00:00 UT   09 52 45.1   +32 37 22    26.496   26.573   93.3    2.1   290   23.9 
2025-11-16 00:00 UT   09 52 44.8   +32 38 03    26.484   26.577   94.3    2.1   289   23.9 
2025-11-17 00:00 UT   09 52 44.3   +32 38 44    26.473   26.582   95.2    2.1   289   23.9 
2025-11-18 00:00 UT   09 52 43.6   +32 39 27    26.461   26.586   96.2    2.1   289   23.9 
2025-11-19 00:00 UT   09 52 42.8   +32 40 10    26.449   26.591   97.2    2.1   288   23.9 
2025-11-20 00:00 UT   09 52 41.8   +32 40 54    26.437   26.595   98.1    2.1   288   23.9 
2025-11-21 00:00 UT   09 52 40.6   +32 41 38    26.425   26.600   99.1    2.1   288   23.9 
2025-11-22 00:00 UT   09 52 39.2   +32 42 24    26.414   26.605  100.0    2.1   287   23.9 
2025-11-23 00:00 UT   09 52 37.7   +32 43 10    26.402   26.609  101.0    2.1   287   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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