C/2025 D1 (Groeller)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Today	24 Dec 2025	18.6	14.677 AU	13.951 AU	09h28m	+33°12'	136.2°	2.7°	270°
Nearest approach	3 Feb 2028	18.3	14.126 AU	13.142 AU	08h58m	+13°41'	176.6°	0.2°	32°
Perihelion	21 May 2028	18.5	14.117 AU	14.442 AU	08h41m	+12°17'	69.4°	3.8°	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. (1.2 + 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/2025 D1 (Groeller) are:

    e (Eccentricity)                : 1.0031500
    q (Perihelion distance)         : 14.1174910
    i (Inclination)                 : 84.45420
    Ω (Longitude of ascending node) : 312.90200
    ω (Argument of perihelion)      : 185.92500
    L (Longitude of perihelion)     : 313.47663
    B (Latitude of perihelion)      : -5.89717
    T (Time of perihelion passage)  : 2461912.73790

    Epoch                           : 2025 Dec 24
    Reference                       : MPEC 2025-UQ3

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-23 00:00 UT   09 29 26.5   +33 12 06    13.976   14.679  134.3    2.7   271   18.6 
2025-12-24 00:00 UT   09 29 11.7   +33 12 29    13.963   14.678  135.3    2.7   271   18.6 
2025-12-24 23:28 UT   09 28 57.0   +33 12 51    13.951   14.677  136.2    2.7   270   18.6 
2025-12-25 00:00 UT   09 28 56.7   +33 12 52    13.951   14.677  136.3    2.7   270   18.6 
2025-12-26 00:00 UT   09 28 41.4   +33 13 15    13.939   14.676  137.2    2.6   269   18.6 
2025-12-27 00:00 UT   09 28 25.8   +33 13 37    13.927   14.675  138.2    2.6   269   18.6 
2025-12-28 00:00 UT   09 28 09.9   +33 13 60    13.915   14.673  139.2    2.5   268   18.6 
2025-12-29 00:00 UT   09 27 53.8   +33 14 22    13.904   14.672  140.1    2.5   267   18.6 
2025-12-30 00:00 UT   09 27 37.4   +33 14 44    13.893   14.671  141.1    2.4   266   18.6 
2025-12-31 00:00 UT   09 27 20.8   +33 15 06    13.882   14.670  142.0    2.4   266   18.6 
2026-01-01 00:00 UT   09 27 03.9   +33 15 28    13.871   14.668  143.0    2.3   265   18.6 
2026-01-02 00:00 UT   09 26 46.7   +33 15 49    13.861   14.667  143.9    2.3   264   18.6 
2026-01-03 00:00 UT   09 26 29.4   +33 16 09    13.851   14.666  144.9    2.2   263   18.6 

    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.