C/2018 U1 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	18 Jun 2021	15.2	5.094 AU	4.132 AU	17h19m	-03°37'	159.1°	4.1°	161°
Perihelion	1 Nov 2021	15.9	4.985 AU	5.817 AU	16h31m	-22°09'	30.2°	5.7°	99°
Today	18 Sep 2025	20.2	11.038 AU	11.370 AU	08h16m	-50°19'	68.3°	4.9°	238°

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 C/2018 U1 (Lemmon) are:

            e (Eccentricity)                : 0.9999090
            q (Perihelion distance)         : 4.9847080
            i (Inclination)                 : 108.32590
            Ω (Longitude of ascending node) : 75.51240
            ω (Argument of perihelion)      : 180.33180
            L (Longitude of perihelion)     : 75.40807
            B (Latitude of perihelion)      : -0.31497
            T (Time of perihelion passage)  : 2459520.46770

            Epoch                           : 2025 Sep 17
            Reference                       : MPC184408

            Classification(s):              : Nearly isotropic; New (a > 10000 AU)
        

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 (5.00 + 5 log[∆] + 10.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 6.31 + 5 log[∆] + 8.25 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
2025-09-18 00:00 UT   08 15 57.6   -50 17 52    11.369   11.036   68.2    4.9   237   20.2 
2025-09-18 11:17 UT   08 16 02.9   -50 19 22    11.370   11.038   68.3    4.9   238   20.2 
2025-09-19 00:00 UT   08 16 08.7   -50 21 04    11.372   11.041   68.4    4.9   238   20.2 
2025-09-20 00:00 UT   08 16 19.3   -50 24 19    11.374   11.047   68.5    4.9   239   20.2 
2025-09-21 00:00 UT   08 16 29.5   -50 27 37    11.377   11.052   68.7    4.9   240   20.2 
2025-09-22 00:00 UT   08 16 39.3   -50 30 57    11.379   11.057   68.9    4.9   241   20.2 
2025-09-23 00:00 UT   08 16 48.6   -50 34 19    11.381   11.063   69.1    4.9   242   20.2 
2025-09-24 00:00 UT   08 16 57.5   -50 37 43    11.383   11.068   69.3    4.9   243   20.2 
2025-09-25 00:00 UT   08 17 05.9   -50 41 09    11.385   11.074   69.4    4.9   244   20.2 
2025-09-26 00:00 UT   08 17 13.9   -50 44 38    11.387   11.079   69.6    4.9   245   20.2 
2025-09-27 00:00 UT   08 17 21.4   -50 48 08    11.389   11.084   69.9    4.9   246   20.2 
2025-09-28 00:00 UT   08 17 28.5   -50 51 40    11.391   11.090   70.1    4.9   247   20.2 

    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.