C/2021 T1 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	5 Oct 2021	19.1	3.061 AU	2.239 AU	23h40m	+43°48'	138.5°	12.5°	155°
Perihelion	15 Oct 2021	19.1	3.059 AU	2.266 AU	23h04m	+41°04'	135.7°	13.2°	128°
Today	13 Dec 2025	29.0	12.209 AU	13.144 AU	16h14m	-16°09'	17.5°	1.4°	296°

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. The light curve is based on the absolute magnitude and slope parameter as calculated from an MPEC, or the latest values provided by the minor planet center. (12.5 + 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 C/2021 T1 (Lemmon) are:

    e (Eccentricity)                : 0.9990430
    q (Perihelion distance)         : 3.0594940
    i (Inclination)                 : 140.34420
    Ω (Longitude of ascending node) : 56.85020
    ω (Argument of perihelion)      : 51.58000
    L (Longitude of perihelion)     : 12.70301
    B (Latitude of perihelion)      : 29.99963
    T (Time of perihelion passage)  : 2459502.57040
    P (Orbital period in years)     : 180761.74

    Epoch                           : 2025 Nov 12
    Reference                       : MPEC 2022-OB6

    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
2025-12-12 00:00 UT   16 14 25.4   -16 08 01    13.143   12.200   16.0    1.3   298   29.0 
2025-12-13 00:00 UT   16 14 40.0   -16 09 07    13.144   12.206   16.9    1.3   297   29.0 
2025-12-13 14:25 UT   16 14 48.8   -16 09 46    13.144   12.209   17.5    1.4   296   29.0 
2025-12-14 00:00 UT   16 14 54.6   -16 10 12    13.145   12.212   17.8    1.4   296   29.0 
2025-12-15 00:00 UT   16 15 09.0   -16 11 16    13.145   12.218   18.7    1.5   295   29.0 
2025-12-16 00:00 UT   16 15 23.4   -16 12 20    13.146   12.224   19.7    1.6   294   29.0 
2025-12-17 00:00 UT   16 15 37.6   -16 13 22    13.146   12.230   20.6    1.6   293   29.0 
2025-12-18 00:00 UT   16 15 51.8   -16 14 25    13.145   12.236   21.5    1.7   293   29.0 
2025-12-19 00:00 UT   16 16 05.8   -16 15 26    13.145   12.242   22.5    1.8   292   29.0 
2025-12-20 00:00 UT   16 16 19.7   -16 16 27    13.144   12.248   23.4    1.8   292   29.0 
2025-12-21 00:00 UT   16 16 33.6   -16 17 27    13.143   12.254   24.3    1.9   291   29.0 
2025-12-22 00:00 UT   16 16 47.2   -16 18 26    13.142   12.260   25.3    2.0   291   29.0 
2025-12-23 00:00 UT   16 17 00.8   -16 19 24    13.140   12.266   26.2    2.0   290   29.0 

    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.