C/2013 A1 (Siding Spring)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	4 Sep 2014	9.1	1.583 AU	0.889 AU	21h34m	-73°18'	113.0°	35.9°	21°
Perihelion	24 Oct 2014	10.3	1.411 AU	1.745 AU	17h36m	-21°44'	53.9°	34.7°	91°
Today	25 Jul 2025	23.8	26.041 AU	26.974 AU	09h40m	+33°01'	22.8°	0.9°	59°

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.)

The orbital elements of C/2013 A1 (Siding Spring) are:

            e (Eccentricity)                : 0.9998840
            q (Perihelion distance)         : 1.4113330
            i (Inclination)                 : 129.15450
            Ω (Longitude of ascending node) : 300.88820
            ω (Argument of perihelion)      : 2.53870
            L (Longitude of perihelion)     : 299.28460
            B (Latitude of perihelion)      : 1.96837
            T (Time of perihelion passage)  : 2456954.82720

            Epoch                           : 2020 Sep 26
            Reference                       : MPC103843

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

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. 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. (8.20 + 5 log[∆] + 6.00 log[r]).

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-07-25 00:00 UT   09 40 12.0   +33 01 18    26.973   26.040   22.8    0.9    60   23.8 
2025-07-25 03:13 UT   09 40 13.2   +33 01 11    26.974   26.041   22.8    0.9    59   23.8 
2025-07-26 00:00 UT   09 40 20.6   +33 00 22    26.981   26.045   22.3    0.8    58   23.8 
2025-07-27 00:00 UT   09 40 29.3   +32 59 27    26.989   26.050   21.8    0.8    56   23.9 
2025-07-28 00:00 UT   09 40 38.0   +32 58 32    26.997   26.054   21.3    0.8    54   23.9 
2025-07-29 00:00 UT   09 40 46.7   +32 57 38    27.005   26.059   20.8    0.8    51   23.9 
2025-07-30 00:00 UT   09 40 55.5   +32 56 44    27.012   26.063   20.3    0.8    49   23.9 
2025-07-31 00:00 UT   09 41 04.3   +32 55 51    27.019   26.068   19.9    0.8    47   23.9 
2025-08-01 00:00 UT   09 41 13.1   +32 54 58    27.026   26.073   19.6    0.7    44   23.9 
2025-08-02 00:00 UT   09 41 22.0   +32 54 05    27.033   26.077   19.2    0.7    42   23.9 
2025-08-03 00:00 UT   09 41 30.9   +32 53 14    27.039   26.082   18.9    0.7    39   23.9 
2025-08-04 00:00 UT   09 41 39.8   +32 52 22    27.045   26.087   18.6    0.7    36   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.