P/2017 Y3 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	4 Feb 2018	18.8	1.277 AU	1.505 AU	17h26m	-02°08'	57.2°	40.5°	288°
Perihelion	6 Feb 2018	18.8	1.277 AU	1.505 AU	17h33m	-01°59'	57.2°	40.5°	287°
Today	22 Jun 2025	34.5	14.872 AU	15.257 AU	02h08m	-09°17'	65.9°	3.6°	239°

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)                : 0.8696340
            q (Perihelion distance)         : 1.2768460
            i (Inclination)                 : 27.63090
            Ω (Longitude of ascending node) : 154.02320
            ω (Argument of perihelion)      : 67.32480
            L (Longitude of perihelion)     : 218.77544
            B (Latitude of perihelion)      : 25.33604
            T (Time of perihelion passage)  : 2458155.87180
            P (Orbital period in years)     : 30.65

            Epoch                           : 2025 Jun 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 16.85 + 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
2025-06-22 00:00 UT   02 08 44.0   -09 16 54    15.260   14.871   65.7    3.6   239   34.5 
2025-06-22 05:14 UT   02 08 46.1   -09 17 01    15.257   14.872   65.9    3.6   239   34.5 
2025-06-23 00:00 UT   02 08 53.6   -09 17 26    15.248   14.874   66.6    3.6   239   34.5 
2025-06-24 00:00 UT   02 09 03.0   -09 17 60    15.236   14.876   67.4    3.6   240   34.5 
2025-06-25 00:00 UT   02 09 12.2   -09 18 35    15.225   14.879   68.3    3.6   240   34.5 
2025-06-26 00:00 UT   02 09 21.2   -09 19 13    15.213   14.881   69.1    3.7   240   34.5 
2025-06-27 00:00 UT   02 09 30.0   -09 19 52    15.201   14.884   70.0    3.7   241   34.5 
2025-06-28 00:00 UT   02 09 38.6   -09 20 33    15.188   14.886   70.9    3.7   241   34.5 
2025-06-29 00:00 UT   02 09 46.9   -09 21 16    15.176   14.889   71.7    3.7   242   34.5 
2025-06-30 00:00 UT   02 09 55.1   -09 22 01    15.164   14.891   72.6    3.7   242   34.5 
2025-07-01 00:00 UT   02 10 03.1   -09 22 47    15.152   14.894   73.4    3.8   242   34.5 
2025-07-02 00:00 UT   02 10 10.9   -09 23 36    15.139   14.896   74.3    3.8   243   34.5 

    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.