P/2017 Y3 (Leonard)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	4 Feb 2018	18.8	1.272 AU	1.495 AU	17h25m	-02°08'	57.4°	40.8°	288°
Perihelion	6 Feb 2018	18.8	1.272 AU	1.495 AU	17h34m	-01°56'	57.4°	40.8°	287°
Today	24 Jun 2026	34.9	15.727 AU	16.123 AU	02h17m	-09°11'	65.4°	3.4°	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.)

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)                : 0.8701090
    q (Perihelion distance)         : 1.2717230
    i (Inclination)                 : 27.65400
    Ω (Longitude of ascending node) : 154.09000
    ω (Argument of perihelion)      : 67.22290
    L (Longitude of perihelion)     : 218.72706
    B (Latitude of perihelion)      : 25.33672
    T (Time of perihelion passage)  : 2458156.33200
    P (Orbital period in years)     : 30.64

    Epoch                           : 2026 May 29
    Reference                       : MPC194154

    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
2026-06-23 00:00 UT   02 17 30.5   -09 11 27    16.136   15.725   64.5    3.3   238   34.9 
2026-06-24 00:00 UT   02 17 39.8   -09 11 57    16.124   15.727   65.3    3.4   239   34.9 
2026-06-24 01:39 UT   02 17 40.4   -09 11 59    16.123   15.727   65.4    3.4   239   34.9 
2026-06-25 00:00 UT   02 17 48.9   -09 12 29    16.112   15.729   66.2    3.4   239   34.9 
2026-06-26 00:00 UT   02 17 57.9   -09 13 02    16.100   15.732   67.0    3.4   240   34.9 
2026-06-27 00:00 UT   02 18 06.7   -09 13 38    16.088   15.734   67.9    3.4   240   34.9 
2026-06-28 00:00 UT   02 18 15.3   -09 14 15    16.076   15.736   68.7    3.5   240   34.9 
2026-06-29 00:00 UT   02 18 23.7   -09 14 54    16.064   15.738   69.6    3.5   241   34.9 
2026-06-30 00:00 UT   02 18 31.9   -09 15 34    16.051   15.740   70.4    3.5   241   34.9 
2026-07-01 00:00 UT   02 18 39.9   -09 16 17    16.039   15.742   71.3    3.5   242   34.9 
2026-07-02 00:00 UT   02 18 47.7   -09 17 01    16.026   15.744   72.1    3.5   242   34.9 
2026-07-03 00:00 UT   02 18 55.4   -09 17 46    16.014   15.746   73.0    3.5   242   34.9 
2026-07-04 00:00 UT   02 19 02.8   -09 18 34    16.001   15.749   73.8    3.6   243   34.9 

    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.