C/2013 U1 (Catalina)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	4 Sep 2013	18.6	2.520 AU	1.655 AU	20h49m	+17°24'	141.0°	14.6°	127°
Perihelion	20 Nov 2013	19.0	2.400 AU	2.140 AU	21h51m	+03°56'	92.8°	24.3°	70°
Today	23 Dec 2025	32.6	18.833 AU	18.547 AU	10h34m	-11°28'	105.4°	2.9°	298°

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. (13.5 + 5 log[∆] + 10.0 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 U1 (Catalina) are:

    e (Eccentricity)                : 0.7977070
    q (Perihelion distance)         : 2.4001990
    i (Inclination)                 : 23.96080
    Ω (Longitude of ascending node) : 211.11160
    ω (Argument of perihelion)      : 143.04200
    L (Longitude of perihelion)     : 176.60052
    B (Latitude of perihelion)      : 14.13256
    T (Time of perihelion passage)  : 2456617.49060
    P (Orbital period in years)     : 40.87

    Epoch                           : 2020 Sep 26
    Reference                       : MPC 86643

    Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); Halley type (P < 200 years)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-22 00:00 UT   10 34 47.2   -11 28 03    18.563   18.831  104.4    2.9   298   32.6 
2025-12-23 00:00 UT   10 34 43.6   -11 28 40    18.549   18.833  105.3    2.9   298   32.6 
2025-12-23 02:46 UT   10 34 43.1   -11 28 44    18.547   18.833  105.4    2.9   298   32.6 
2025-12-24 00:00 UT   10 34 39.8   -11 29 16    18.534   18.834  106.3    2.9   299   32.6 
2025-12-25 00:00 UT   10 34 35.8   -11 29 49    18.521   18.836  107.3    2.9   299   32.6 
2025-12-26 00:00 UT   10 34 31.6   -11 30 22    18.507   18.838  108.2    2.8   300   32.6 
2025-12-27 00:00 UT   10 34 27.2   -11 30 52    18.493   18.839  109.2    2.8   300   32.6 
2025-12-28 00:00 UT   10 34 22.6   -11 31 22    18.479   18.841  110.2    2.8   300   32.6 
2025-12-29 00:00 UT   10 34 17.8   -11 31 49    18.466   18.843  111.1    2.8   301   32.6 
2025-12-30 00:00 UT   10 34 12.9   -11 32 15    18.452   18.844  112.1    2.8   301   32.6 
2025-12-31 00:00 UT   10 34 07.7   -11 32 39    18.439   18.846  113.1    2.8   301   32.6 
2026-01-01 00:00 UT   10 34 02.4   -11 33 02    18.426   18.848  114.0    2.7   302   32.6 
2026-01-02 00:00 UT   10 33 56.8   -11 33 23    18.413   18.850  115.0    2.7   302   32.6 

    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.