C/2013 A1 (Siding Spring)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	6 Sep 2014	9.2	1.573 AU	0.901 AU	21h36m	-74°42'	110.8°	36.8°	22°
Perihelion	26 Oct 2014	10.3	1.392 AU	1.761 AU	17h39m	-21°47'	52.0°	34.3°	91°
Today	30 Aug 2026	24.2	27.890 AU	28.791 AU	09h42m	+32°13'	26.3°	0.9°	329°

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)                : 1.0000920
    q (Perihelion distance)         : 1.3917240
    i (Inclination)                 : 128.68700
    Ω (Longitude of ascending node) : 301.18400
    ω (Argument of perihelion)      : 2.54170
    L (Longitude of perihelion)     : 299.59464
    B (Latitude of perihelion)      : 1.98373
    T (Time of perihelion passage)  : 2456957.48660

    Epoch                           : 2026 Aug 27
    Reference                       : MPC194130

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-08-29 00:00 UT   09 42 01.8   +32 14 09    28.793   27.882   25.1    0.9   332   24.2 
2026-08-30 00:00 UT   09 42 10.1   +32 13 38    28.792   27.887   25.8    0.9   331   24.2 
2026-08-30 17:48 UT   09 42 16.2   +32 13 16    28.791   27.890   26.3    0.9   329   24.2 
2026-08-31 00:00 UT   09 42 18.3   +32 13 08    28.791   27.891   26.5    0.9   329   24.2 
2026-09-01 00:00 UT   09 42 26.6   +32 12 38    28.789   27.896   27.2    0.9   328   24.2 
2026-09-02 00:00 UT   09 42 34.8   +32 12 10    28.788   27.900   27.9    1.0   326   24.2 
2026-09-03 00:00 UT   09 42 42.9   +32 11 42    28.786   27.905   28.6    1.0   325   24.2 
2026-09-04 00:00 UT   09 42 51.0   +32 11 14    28.783   27.909   29.3    1.0   324   24.2 
2026-09-05 00:00 UT   09 42 59.1   +32 10 48    28.781   27.914   30.1    1.0   323   24.2 
2026-09-06 00:00 UT   09 43 07.1   +32 10 22    28.778   27.918   30.9    1.1   322   24.2 
2026-09-07 00:00 UT   09 43 15.1   +32 09 57    28.775   27.923   31.6    1.1   321   24.2 
2026-09-08 00:00 UT   09 43 23.0   +32 09 33    28.772   27.927   32.4    1.1   320   24.2 
2026-09-09 00:00 UT   09 43 30.8   +32 09 10    28.769   27.932   33.2    1.1   319   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.