C/2025 D1 (Groeller)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Today	3 Dec 2025	18.6	14.704 AU	14.260 AU	09h33m	+33°05'	115.0°	3.5°	281°
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	14.118 AU	14.439 AU	08h41m	+12°17'	69.6°	3.9°	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)                : 1.0031450
    q (Perihelion distance)         : 14.1177180
    i (Inclination)                 : 84.45490
    Ω (Longitude of ascending node) : 312.90180
    ω (Argument of perihelion)      : 185.92050
    L (Longitude of perihelion)     : 313.47592
    B (Latitude of perihelion)      : -5.89270
    T (Time of perihelion passage)  : 2461912.57370

    Epoch                           : 2025 Dec 02
    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
2025-12-02 00:00 UT   09 33 25.6   +33 05 12    14.283   14.706  113.6    3.5   282   18.6 
2025-12-03 00:00 UT   09 33 17.5   +33 05 26    14.267   14.705  114.6    3.5   281   18.6 
2025-12-03 10:37 UT   09 33 13.7   +33 05 32    14.260   14.704  115.0    3.5   281   18.6 
2025-12-04 00:00 UT   09 33 09.0   +33 05 41    14.251   14.703  115.6    3.5   281   18.6 
2025-12-05 00:00 UT   09 33 00.1   +33 05 57    14.235   14.702  116.6    3.4   280   18.6 
2025-12-06 00:00 UT   09 32 51.0   +33 06 13    14.219   14.701  117.6    3.4   280   18.6 
2025-12-07 00:00 UT   09 32 41.5   +33 06 30    14.203   14.700  118.5    3.4   280   18.6 
2025-12-08 00:00 UT   09 32 31.7   +33 06 48    14.188   14.698  119.5    3.3   279   18.6 
2025-12-09 00:00 UT   09 32 21.5   +33 07 06    14.172   14.697  120.5    3.3   279   18.6 
2025-12-10 00:00 UT   09 32 11.1   +33 07 25    14.157   14.696  121.5    3.3   278   18.6 
2025-12-11 00:00 UT   09 32 00.3   +33 07 45    14.142   14.695  122.5    3.2   278   18.6 
2025-12-12 00:00 UT   09 31 49.2   +33 08 05    14.127   14.693  123.5    3.2   277   18.6 
2025-12-13 00:00 UT   09 31 37.8   +33 08 25    14.112   14.692  124.5    3.2   277   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.