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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 AU0.907 AU 21h37m-74°41'110.8°36.7°22°
Perihelion27 Oct 201410.31.393 AU1.771 AU 17h40m-21°47'51.7°34.0°91°
Today18 Mar 202623.927.143 AU26.439 AU 09h35m+34°08'134.2°1.5°129°
C/2013 A1 (Siding Spring)- 2026-03-18
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)                : 1.0001640
    q (Perihelion distance)         : 1.3933260
    i (Inclination)                 : 128.68780
    Ω (Longitude of ascending node) : 301.18360
    ω (Argument of perihelion)      : 2.56560
    L (Longitude of perihelion)     : 299.57925
    B (Latitude of perihelion)      : 2.00235
    T (Time of perihelion passage)  : 2456958.12830

    Epoch                           : 2026 Mar 16
    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
2026-03-17 00:00 UT   09 36 11.7   +34 08 28    26.416   27.136  135.6    1.5   130   23.9 
2026-03-18 00:00 UT   09 36 02.7   +34 08 31    26.431   27.141  134.7    1.5   130   23.9 
2026-03-18 12:12 UT   09 35 58.1   +34 08 33    26.439   27.143  134.2    1.5   129   23.9 
2026-03-19 00:00 UT   09 35 53.7   +34 08 34    26.446   27.145  133.8    1.5   129   23.9 
2026-03-20 00:00 UT   09 35 44.9   +34 08 35    26.462   27.150  132.9    1.5   128   23.9 
2026-03-21 00:00 UT   09 35 36.2   +34 08 36    26.478   27.154  132.0    1.6   128   23.9 
2026-03-22 00:00 UT   09 35 27.6   +34 08 35    26.494   27.159  131.0    1.6   127   23.9 
2026-03-23 00:00 UT   09 35 19.1   +34 08 33    26.510   27.164  130.1    1.6   126   23.9 
2026-03-24 00:00 UT   09 35 10.8   +34 08 30    26.527   27.168  129.2    1.6   126   23.9 
2026-03-25 00:00 UT   09 35 02.6   +34 08 26    26.543   27.173  128.3    1.7   125   23.9 
2026-03-26 00:00 UT   09 34 54.5   +34 08 21    26.560   27.177  127.3    1.7   125   23.9 
2026-03-27 00:00 UT   09 34 46.5   +34 08 15    26.577   27.182  126.4    1.7   124   23.9 
2026-03-28 00:00 UT   09 34 38.7   +34 08 08    26.594   27.186  125.5    1.7   124   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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