P/2017 Y3 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	4 Feb 2018	18.8	1.276 AU	1.505 AU	17h26m	-02°09'	57.2°	40.5°	288°
Perihelion	6 Feb 2018	18.8	1.276 AU	1.505 AU	17h33m	-01°59'	57.2°	40.5°	287°
Today	22 Aug 2025	34.4	15.024 AU	14.498 AU	02h11m	-10°39'	119.7°	3.4°	262°

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.)

The orbital elements of P/2017 Y3 (Leonard) are:

            e (Eccentricity)                : 0.8696910
            q (Perihelion distance)         : 1.2761230
            i (Inclination)                 : 27.63560
            Ω (Longitude of ascending node) : 154.03640
            ω (Argument of perihelion)      : 67.30540
            L (Longitude of perihelion)     : 218.76665
            B (Latitude of perihelion)      : 25.33645
            T (Time of perihelion passage)  : 2458155.84260
            P (Orbital period in years)     : 30.65

            Epoch                           : 2025 Aug 21
            Reference                       : MPC111770

            Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); Halley type (P < 200 years)
        

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. The gray curve is based on the absolute magnitude and slope parameter as calculated from the original MPEC, or the latest values provided by the MPC (16.50 + 5 log[∆] + 10.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 16.86 + 5 log[∆] + 10.00 log[r]).

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-08-22 00:00 UT   02 11 32.1   -10 38 42    14.501   15.023  119.4    3.4   262   34.4 
2025-08-22 07:39 UT   02 11 30.5   -10 39 19    14.498   15.024  119.7    3.4   262   34.4 
2025-08-23 00:00 UT   02 11 27.1   -10 40 40    14.490   15.026  120.3    3.3   263   34.4 
2025-08-24 00:00 UT   02 11 21.9   -10 42 39    14.480   15.028  121.2    3.3   263   34.4 
2025-08-25 00:00 UT   02 11 16.5   -10 44 38    14.470   15.031  122.1    3.3   264   34.4 
2025-08-26 00:00 UT   02 11 10.8   -10 46 38    14.459   15.033  122.9    3.2   264   34.4 
2025-08-27 00:00 UT   02 11 04.9   -10 48 38    14.450   15.036  123.8    3.2   265   34.4 
2025-08-28 00:00 UT   02 10 58.7   -10 50 39    14.440   15.038  124.7    3.2   265   34.4 
2025-08-29 00:00 UT   02 10 52.3   -10 52 41    14.430   15.041  125.6    3.1   266   34.4 
2025-08-30 00:00 UT   02 10 45.6   -10 54 42    14.421   15.043  126.5    3.1   267   34.4 
2025-08-31 00:00 UT   02 10 38.8   -10 56 44    14.411   15.045  127.3    3.1   267   34.4 
2025-09-01 00:00 UT   02 10 31.6   -10 58 47    14.402   15.048  128.2    3.0   268   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.