P/2017 Y3 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	4 Feb 2018	18.8	1.276 AU	1.504 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	16 Sep 2025	34.4	15.084 AU	14.291 AU	02h08m	-11°29'	140.9°	2.4°	280°

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)                : 0.8697220
            q (Perihelion distance)         : 1.2757420
            i (Inclination)                 : 27.63780
            Ω (Longitude of ascending node) : 154.04270
            ω (Argument of perihelion)      : 67.29610
            L (Longitude of perihelion)     : 218.76242
            B (Latitude of perihelion)      : 25.33660
            T (Time of perihelion passage)  : 2458155.85300
            P (Orbital period in years)     : 30.64

            Epoch                           : 2025 Sep 15
            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
2025-09-16 00:00 UT   02 08 18.5   -11 29 28    14.291   15.084  140.9    2.4   280   34.4 
2025-09-16 00:07 UT   02 08 18.4   -11 29 29    14.291   15.084  140.9    2.4   280   34.4 
2025-09-17 00:00 UT   02 08 08.0   -11 31 30    14.285   15.087  141.7    2.4   281   34.4 
2025-09-18 00:00 UT   02 07 57.3   -11 33 31    14.280   15.089  142.5    2.3   282   34.4 
2025-09-19 00:00 UT   02 07 46.4   -11 35 31    14.274   15.092  143.3    2.3   283   34.4 
2025-09-20 00:00 UT   02 07 35.3   -11 37 31    14.270   15.094  144.0    2.2   284   34.4 
2025-09-21 00:00 UT   02 07 24.1   -11 39 31    14.265   15.097  144.8    2.2   285   34.4 
2025-09-22 00:00 UT   02 07 12.7   -11 41 30    14.260   15.099  145.5    2.2   287   34.4 
2025-09-23 00:00 UT   02 07 01.1   -11 43 28    14.256   15.101  146.3    2.1   288   34.4 
2025-09-24 00:00 UT   02 06 49.4   -11 45 26    14.252   15.104  147.0    2.1   289   34.4 
2025-09-25 00:00 UT   02 06 37.5   -11 47 22    14.249   15.106  147.7    2.0   291   34.4 
2025-09-26 00:00 UT   02 06 25.4   -11 49 18    14.245   15.109  148.4    2.0   292   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.