21P/Giacobini-Zinner
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	21 Mar 2025	11.3	1.011 AU	2.002 AU	00h03m	+04°02'	4.0°	3.9°	9°
Perihelion	25 Mar 2025	11.3	1.009 AU	2.003 AU	00h22m	+04°29'	3.0°	3.0°	28°
Today	24 Dec 2025	18.2	3.137 AU	2.681 AU	09h59m	-21°47'	108.6°	17.3°	306°

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. This lightcurve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 9.8 + 5 log[∆] + 12.6 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 21P/Giacobini-Zinner are:

    e (Eccentricity)                : 0.7110890
    q (Perihelion distance)         : 1.0087010
    i (Inclination)                 : 32.05320
    Ω (Longitude of ascending node) : 195.30880
    ω (Argument of perihelion)      : 172.93960
    L (Longitude of perihelion)     : 189.31619
    B (Latitude of perihelion)      : 3.74018
    T (Time of perihelion passage)  : 2460759.85950
    P (Orbital period in years)     : 6.52

    Epoch                           : 2025 Dec 24
    Reference                       : MPEC 2025-W75

    Classification(s):              : Ecliptic; Jupiter family
    Tisserand (Jupiter)             : 2.467

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-23 00:00 UT   10 00 33.3   -21 39 52     2.691    3.124  107.0   17.5   305   18.2 
2025-12-24 00:00 UT   10 00 11.7   -21 44 14     2.686    3.131  107.9   17.4   305   18.2 
2025-12-24 20:09 UT   09 59 52.5   -21 47 46     2.681    3.137  108.6   17.3   306   18.2 
2025-12-25 00:00 UT   09 59 48.8   -21 48 26     2.680    3.138  108.8   17.3   306   18.2 
2025-12-26 00:00 UT   09 59 24.4   -21 52 25     2.675    3.145  109.6   17.1   307   18.2 
2025-12-27 00:00 UT   09 58 58.7   -21 56 11     2.670    3.153  110.5   17.0   307   18.2 
2025-12-28 00:00 UT   09 58 31.7   -21 59 46     2.665    3.160  111.4   16.8   308   18.2 
2025-12-29 00:00 UT   09 58 03.3   -22 03 07     2.660    3.167  112.3   16.7   309   18.2 
2025-12-30 00:00 UT   09 57 33.6   -22 06 16     2.655    3.174  113.2   16.5   310   18.2 
2025-12-31 00:00 UT   09 57 02.7   -22 09 12     2.651    3.181  114.1   16.4   310   18.2 
2026-01-01 00:00 UT   09 56 30.4   -22 11 54     2.646    3.188  115.0   16.2   311   18.2 
2026-01-02 00:00 UT   09 55 56.9   -22 14 22     2.642    3.195  115.8   16.1   312   18.2 
2026-01-03 00:00 UT   09 55 22.1   -22 16 37     2.637    3.203  116.7   15.9   313   18.2 

    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.