C/2013 A1 (Siding Spring)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	6 Sep 2014	9.2	1.574 AU	0.902 AU	21h36m	-74°42'	110.8°	36.8°	22°
Perihelion	27 Oct 2014	10.3	1.392 AU	1.762 AU	17h39m	-21°47'	52.0°	34.2°	91°
Today	6 Aug 2026	24.2	27.780 AU	28.745 AU	09h38m	+32°28'	17.6°	0.6°	29°

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)                : 1.0001000
    q (Perihelion distance)         : 1.3918960
    i (Inclination)                 : 128.68700
    Ω (Longitude of ascending node) : 301.18400
    ω (Argument of perihelion)      : 2.54430
    L (Longitude of perihelion)     : 299.59301
    B (Latitude of perihelion)      : 1.98575
    T (Time of perihelion passage)  : 2456957.56210

    Epoch                           : 2026 Aug 05
    Reference                       : MPC194130

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-08-05 00:00 UT   09 38 37.5   +32 29 57    28.738   27.774   17.8    0.6    33   24.2 
2026-08-06 00:00 UT   09 38 46.0   +32 29 11    28.743   27.779   17.6    0.6    30   24.2 
2026-08-06 07:29 UT   09 38 48.6   +32 28 57    28.745   27.780   17.6    0.6    29   24.2 
2026-08-07 00:00 UT   09 38 54.5   +32 28 25    28.748   27.783   17.5    0.6    27   24.2 
2026-08-08 00:00 UT   09 39 03.0   +32 27 40    28.753   27.788   17.4    0.6    24   24.2 
2026-08-09 00:00 UT   09 39 11.5   +32 26 55    28.758   27.792   17.4    0.6    21   24.2 
2026-08-10 00:00 UT   09 39 20.1   +32 26 11    28.762   27.797   17.4    0.6    17   24.2 
2026-08-11 00:00 UT   09 39 28.7   +32 25 27    28.766   27.801   17.5    0.6    14   24.2 
2026-08-12 00:00 UT   09 39 37.2   +32 24 44    28.770   27.806   17.6    0.6    11   24.2 
2026-08-13 00:00 UT   09 39 45.8   +32 24 01    28.773   27.810   17.7    0.6     8   24.2 
2026-08-14 00:00 UT   09 39 54.4   +32 23 20    28.776   27.815   17.9    0.6     5   24.2 
2026-08-15 00:00 UT   09 40 03.0   +32 22 38    28.779   27.819   18.2    0.7     2   24.2 
2026-08-16 00:00 UT   09 40 11.5   +32 21 58    28.782   27.824   18.5    0.7   360   24.2 

    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.