C/2018 U1 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	18 Jun 2021	15.2	5.091 AU	4.129 AU	17h19m	-03°36'	159.0°	4.1°	162°
Perihelion	1 Nov 2021	15.9	4.982 AU	5.810 AU	16h31m	-22°06'	30.6°	5.8°	99°
Today	30 May 2026	20.8	12.406 AU	12.613 AU	07h10m	-44°37'	76.0°	4.5°	142°

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 6.3 + 5 log[∆] + 8.3 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 C/2018 U1 (Lemmon) are:

    e (Eccentricity)                : 0.9993560
    q (Perihelion distance)         : 4.9818440
    i (Inclination)                 : 108.32830
    Ω (Longitude of ascending node) : 75.49700
    ω (Argument of perihelion)      : 180.28010
    L (Longitude of perihelion)     : 75.40892
    B (Latitude of perihelion)      : -0.26589
    T (Time of perihelion passage)  : 2459519.99930
    P (Orbital period in years)     : 680387.59

    Epoch                           : 2026 May 29
    Reference                       : MPC194157

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-05-29 00:00 UT   07 09 42.1   -44 42 59    12.595   12.398   76.5    4.6   140   20.8 
2026-05-30 00:00 UT   07 09 59.1   -44 39 33    12.606   12.403   76.2    4.6   141   20.8 
2026-05-30 13:37 UT   07 10 08.8   -44 37 38    12.613   12.406   76.0    4.5   142   20.8 
2026-05-31 00:00 UT   07 10 16.3   -44 36 11    12.617   12.409   75.8    4.5   142   20.8 
2026-06-01 00:00 UT   07 10 33.7   -44 32 53    12.629   12.414   75.5    4.5   143   20.9 
2026-06-02 00:00 UT   07 10 51.3   -44 29 38    12.640   12.419   75.2    4.5   144   20.9 
2026-06-03 00:00 UT   07 11 09.1   -44 26 27    12.651   12.425   74.8    4.5   145   20.9 
2026-06-04 00:00 UT   07 11 27.0   -44 23 20    12.662   12.430   74.5    4.5   145   20.9 
2026-06-05 00:00 UT   07 11 45.2   -44 20 17    12.673   12.435   74.2    4.5   146   20.9 
2026-06-06 00:00 UT   07 12 03.5   -44 17 18    12.684   12.441   73.9    4.5   147   20.9 
2026-06-07 00:00 UT   07 12 22.0   -44 14 22    12.694   12.446   73.6    4.5   148   20.9 
2026-06-08 00:00 UT   07 12 40.6   -44 11 31    12.705   12.451   73.3    4.5   149   20.9 
2026-06-09 00:00 UT   07 12 59.4   -44 08 43    12.716   12.457   73.0    4.5   150   20.9 

    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.