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	26 Sep 2026	34.8	15.924 AU	15.081 AU	02h15m	-11°34'	146.2°	2.0°	290°

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
2026-09-25 00:00 UT   02 16 08.3   -11 32 13    15.085   15.922  145.4    2.0   288   34.8 
2026-09-26 00:00 UT   02 15 57.2   -11 34 04    15.081   15.924  146.1    2.0   290   34.8 
2026-09-26 01:08 UT   02 15 56.7   -11 34 09    15.081   15.924  146.2    2.0   290   34.8 
2026-09-27 00:00 UT   02 15 45.9   -11 35 54    15.077   15.926  146.8    2.0   291   34.8 
2026-09-28 00:00 UT   02 15 34.5   -11 37 43    15.073   15.928  147.5    1.9   293   34.8 
2026-09-29 00:00 UT   02 15 23.0   -11 39 32    15.069   15.930  148.2    1.9   294   34.8 
2026-09-30 00:00 UT   02 15 11.3   -11 41 20    15.066   15.932  148.9    1.9   296   34.8 
2026-10-01 00:00 UT   02 14 59.5   -11 43 07    15.063   15.934  149.5    1.8   297   34.8 
2026-10-02 00:00 UT   02 14 47.5   -11 44 53    15.060   15.936  150.1    1.8   299   34.8 
2026-10-03 00:00 UT   02 14 35.4   -11 46 38    15.057   15.938  150.7    1.8   301   34.8 
2026-10-04 00:00 UT   02 14 23.2   -11 48 22    15.055   15.940  151.3    1.7   302   34.8 
2026-10-05 00:00 UT   02 14 10.9   -11 50 05    15.053   15.942  151.8    1.7   304   34.8 
2026-10-06 00:00 UT   02 13 58.4   -11 51 47    15.051   15.944  152.4    1.7   306   34.8 

    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.