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P/2017 Y3 (Leonard)
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach4 Feb 201818.81.275 AU1.504 AU17h26m-02°09'57.2°40.5°288°
Perihelion6 Feb 201818.81.275 AU1.504 AU17h33m-01°59'57.2°40.5°287°
Today18 Oct 202534.415.162 AU14.241 AU02h01m-12°27'156.8°1.5°341°
P/2017 Y3 (Leonard)- 2025-10-18
astro.vanbuitenen.nl


 
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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 16.9 + 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 P/2017 Y3 (Leonard) are: 

    e (Eccentricity)                : 0.8697650
    q (Perihelion distance)         : 1.2752390
    i (Inclination)                 : 27.64040
    Ω (Longitude of ascending node) : 154.04990
    ω (Argument of perihelion)      : 67.28520
    L (Longitude of perihelion)     : 218.75727
    B (Latitude of perihelion)      : 25.33679
    T (Time of perihelion passage)  : 2458155.88800
    P (Orbital period in years)     : 30.64

    Epoch                           : 2025 Oct 17
    Reference                       : MPC111770

    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
2025-10-17 00:00 UT   02 01 45.4   -12 25 38    14.238   15.159  156.8    1.5   338   34.4 
2025-10-18 00:00 UT   02 01 31.2   -12 27 07    14.241   15.162  156.8    1.5   340   34.4 
2025-10-18 03:26 UT   02 01 29.2   -12 27 19    14.241   15.162  156.8    1.5   341   34.4 
2025-10-19 00:00 UT   02 01 17.0   -12 28 34    14.244   15.164  156.7    1.5   343   34.4 
2025-10-20 00:00 UT   02 01 02.7   -12 29 59    14.247   15.166  156.6    1.5   346   34.4 
2025-10-21 00:00 UT   02 00 48.5   -12 31 22    14.251   15.169  156.4    1.5   348   34.4 
2025-10-22 00:00 UT   02 00 34.2   -12 32 43    14.255   15.171  156.2    1.5   351   34.4 
2025-10-23 00:00 UT   02 00 19.8   -12 34 03    14.259   15.174  156.0    1.5   354   34.4 
2025-10-24 00:00 UT   02 00 05.5   -12 35 21    14.264   15.176  155.7    1.5   356   34.4 
2025-10-25 00:00 UT   01 59 51.2   -12 36 36    14.268   15.178  155.4    1.6   358   34.4 
2025-10-26 00:00 UT   01 59 36.9   -12 37 50    14.273   15.181  155.0    1.6     1   34.4 
2025-10-27 00:00 UT   01 59 22.6   -12 39 02    14.279   15.183  154.6    1.6     3   34.4 
2025-10-28 00:00 UT   01 59 08.3   -12 40 12    14.285   15.186  154.2    1.6     5   34.4 




    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.

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