C/2021 T4 (Lemmon)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	20 Jul 2023	8.6	1.490 AU	0.540 AU	19h58m	-55°59'	144.7°	23.2°	359°
Perihelion	31 Jul 2023	9.1	1.482 AU	0.677 AU	16h23m	-43°09'	121.0°	35.9°	87°
Today	21 Dec 2024	19.7	5.886 AU	5.782 AU	12h26m	+18°28'	91.3°	9.6°	294°

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/2021 T4 (Lemmon) are:

            e (Eccentricity)                : 0.9998480
            q (Perihelion distance)         : 1.4822810
            i (Inclination)                 : 160.77830
            Ω (Longitude of ascending node) : 257.89260
            ω (Argument of perihelion)      : 329.79780
            L (Longitude of perihelion)     : 286.68651
            B (Latitude of perihelion)      : -9.53310
            T (Time of perihelion passage)  : 2460157.04570
            P (Orbital period in years)     : 963009.19

            Epoch                           : 2024 Dec 20
            Reference                       : MPEC 2024-N80

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

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 (7.50 + 5 log[∆] + 10.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 8.20 + 5 log[∆] + 9.96 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
2024-12-21 00:00 UT   12 27 04.5   +18 25 52     5.787    5.881   90.6    9.6   295   19.7 
2024-12-21 14:54 UT   12 26 58.9   +18 28 58     5.782    5.886   91.3    9.6   294   19.7 
2024-12-22 00:00 UT   12 26 55.4   +18 30 53     5.778    5.890   91.7    9.6   294   19.7 
2024-12-23 00:00 UT   12 26 45.6   +18 36 00     5.770    5.898   92.7    9.6   294   19.7 
2024-12-24 00:00 UT   12 26 35.0   +18 41 12     5.761    5.907   93.7    9.6   293   19.7 
2024-12-25 00:00 UT   12 26 23.7   +18 46 30     5.752    5.916   94.8    9.5   293   19.7 
2024-12-26 00:00 UT   12 26 11.7   +18 51 53     5.743    5.924   95.8    9.5   293   19.7 
2024-12-27 00:00 UT   12 25 58.9   +18 57 20     5.735    5.933   96.8    9.5   292   19.7 
2024-12-28 00:00 UT   12 25 45.3   +19 02 53     5.726    5.942   97.9    9.4   292   19.7 
2024-12-29 00:00 UT   12 25 31.0   +19 08 31     5.718    5.950   98.9    9.4   292   19.7 
2024-12-30 00:00 UT   12 25 15.8   +19 14 14     5.709    5.959  100.0    9.4   291   19.7 
2024-12-31 00:00 UT   12 24 59.9   +19 20 02     5.701    5.967  101.0    9.3   291   19.7 

    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.