C/2013 A1 (Siding Spring)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	6 Sep 2014	9.2	1.576 AU	0.905 AU	21h37m	-74°43'	110.8°	36.7°	22°
Perihelion	27 Oct 2014	10.3	1.393 AU	1.768 AU	17h40m	-21°47'	51.8°	34.1°	91°
Today	14 May 2026	24.0	27.402 AU	27.536 AU	09h31m	+33°44'	81.3°	2.1°	107°

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)                : 1.0001360
    q (Perihelion distance)         : 1.3925650
    i (Inclination)                 : 128.68430
    Ω (Longitude of ascending node) : 301.18550
    ω (Argument of perihelion)      : 2.55610
    L (Longitude of perihelion)     : 299.58722
    B (Latitude of perihelion)      : 1.99504
    T (Time of perihelion passage)  : 2456957.91550

    Epoch                           : 2026 May 13
    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
2026-05-13 00:00 UT   09 31 27.7   +33 45 50    27.505   27.395   82.7    2.1   107   24.0 
2026-05-14 00:00 UT   09 31 27.4   +33 45 03    27.525   27.400   81.8    2.1   107   24.0 
2026-05-14 12:47 UT   09 31 27.3   +33 44 38    27.536   27.402   81.3    2.1   107   24.0 
2026-05-15 00:00 UT   09 31 27.3   +33 44 15    27.546   27.404   80.9    2.1   106   24.0 
2026-05-16 00:00 UT   09 31 27.4   +33 43 27    27.566   27.409   79.9    2.1   106   24.0 
2026-05-17 00:00 UT   09 31 27.6   +33 42 39    27.587   27.413   79.0    2.1   106   24.0 
2026-05-18 00:00 UT   09 31 28.1   +33 41 50    27.607   27.418   78.1    2.1   106   24.0 
2026-05-19 00:00 UT   09 31 28.6   +33 41 01    27.628   27.422   77.2    2.1   105   24.0 
2026-05-20 00:00 UT   09 31 29.4   +33 40 11    27.648   27.427   76.3    2.1   105   24.0 
2026-05-21 00:00 UT   09 31 30.2   +33 39 20    27.668   27.431   75.4    2.0   105   24.0 
2026-05-22 00:00 UT   09 31 31.3   +33 38 29    27.688   27.436   74.5    2.0   104   24.0 
2026-05-23 00:00 UT   09 31 32.5   +33 37 38    27.708   27.440   73.6    2.0   104   24.0 
2026-05-24 00:00 UT   09 31 33.9   +33 36 46    27.728   27.445   72.7    2.0   104   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.