C/2025 D1 (Groeller)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Today	21 Jan 2026	18.5	14.643 AU	13.715 AU	09h20m	+33°20'	159.9°	1.3°	232°
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	14.444 AU	08h41m	+12°16'	69.2°	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)                : 1.0031440
    q (Perihelion distance)         : 14.1172760
    i (Inclination)                 : 84.45330
    Ω (Longitude of ascending node) : 312.90230
    ω (Argument of perihelion)      : 185.93000
    L (Longitude of perihelion)     : 313.47751
    B (Latitude of perihelion)      : -5.90214
    T (Time of perihelion passage)  : 2461912.92790

    Epoch                           : 2026 Jan 20
    Reference                       : MPEC 2026-A24

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-01-20 00:00 UT   09 21 03.0   +33 20 19    13.723   14.645  159.0    1.4   236   18.5 
2026-01-21 00:00 UT   09 20 42.3   +33 20 25    13.718   14.644  159.6    1.3   234   18.5 
2026-01-21 11:26 UT   09 20 32.5   +33 20 28    13.715   14.643  159.9    1.3   232   18.5 
2026-01-22 00:00 UT   09 20 21.6   +33 20 30    13.713   14.643  160.2    1.3   231   18.5 
2026-01-23 00:00 UT   09 20 00.7   +33 20 35    13.709   14.642  160.7    1.3   228   18.5 
2026-01-24 00:00 UT   09 19 39.7   +33 20 37    13.705   14.640  161.3    1.2   225   18.5 
2026-01-25 00:00 UT   09 19 18.6   +33 20 39    13.701   14.639  161.7    1.2   222   18.5 
2026-01-26 00:00 UT   09 18 57.4   +33 20 39    13.698   14.638  162.1    1.2   219   18.5 
2026-01-27 00:00 UT   09 18 36.1   +33 20 38    13.695   14.637  162.5    1.2   215   18.5 
2026-01-28 00:00 UT   09 18 14.8   +33 20 35    13.692   14.636  162.8    1.1   212   18.5 
2026-01-29 00:00 UT   09 17 53.4   +33 20 31    13.690   14.634  163.0    1.1   208   18.5 
2026-01-30 00:00 UT   09 17 32.0   +33 20 26    13.688   14.633  163.2    1.1   204   18.5 
2026-01-31 00:00 UT   09 17 10.5   +33 20 19    13.686   14.632  163.3    1.1   201   18.5 

    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.