C/2018 U1 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	18 Jun 2021	15.2	5.090 AU	4.128 AU	17h19m	-03°36'	159.0°	4.1°	162°
Perihelion	1 Nov 2021	15.9	4.982 AU	5.810 AU	16h31m	-22°06'	30.7°	5.8°	99°
Today	1 Jul 2026	21.0	12.578 AU	12.939 AU	07h20m	-43°23'	67.1°	4.3°	170°

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)                : 0.9993000
    q (Perihelion distance)         : 4.9816270
    i (Inclination)                 : 108.32890
    Ω (Longitude of ascending node) : 75.49380
    ω (Argument of perihelion)      : 180.27510
    L (Longitude of perihelion)     : 75.40729
    B (Latitude of perihelion)      : -0.26114
    T (Time of perihelion passage)  : 2459519.94450
    P (Orbital period in years)     : 600357.24

    Epoch                           : 2026 Jul 01
    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
2026-06-30 00:00 UT   07 19 59.5   -43 25 26    12.923   12.569   67.4    4.3   169   20.9 
2026-07-01 00:00 UT   07 20 20.3   -43 24 07    12.932   12.574   67.2    4.3   170   20.9 
2026-07-01 19:30 UT   07 20 37.2   -43 23 05    12.939   12.578   67.1    4.3   170   21.0 
2026-07-02 00:00 UT   07 20 41.1   -43 22 51    12.941   12.579   67.0    4.3   170   21.0 
2026-07-03 00:00 UT   07 21 01.8   -43 21 40    12.949   12.585   66.8    4.3   171   21.0 
2026-07-04 00:00 UT   07 21 22.7   -43 20 32    12.958   12.590   66.6    4.3   172   21.0 
2026-07-05 00:00 UT   07 21 43.5   -43 19 29    12.967   12.595   66.4    4.2   173   21.0 
2026-07-06 00:00 UT   07 22 04.3   -43 18 29    12.975   12.601   66.3    4.2   174   21.0 
2026-07-07 00:00 UT   07 22 25.1   -43 17 33    12.983   12.606   66.1    4.2   175   21.0 
2026-07-08 00:00 UT   07 22 46.0   -43 16 42    12.992   12.611   65.9    4.2   176   21.0 
2026-07-09 00:00 UT   07 23 06.8   -43 15 54    13.000   12.617   65.7    4.2   177   21.0 
2026-07-10 00:00 UT   07 23 27.6   -43 15 10    13.008   12.622   65.6    4.2   178   21.0 
2026-07-11 00:00 UT   07 23 48.4   -43 14 30    13.016   12.627   65.4    4.2   179   21.0 

    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.