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C/2021 T4 (Lemmon)
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach20 Jul 20238.61.488 AU0.538 AU 19h58m-56°03'144.6°23.3°359°
Perihelion31 Jul 20239.01.480 AU0.672 AU 16h24m-43°21'121.3°35.9°86°
Today5 Apr 202622.69.581 AU8.897 AU 10h37m+30°31'130.8°4.5°132°
C/2021 T4 (Lemmon)- 2026-04-05
astro.vanbuitenen.nl


 
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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 8.2 + 5 log[∆] + 9.8 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 T4 (Lemmon) are: 

    e (Eccentricity)                : 0.9994290
    q (Perihelion distance)         : 1.4803970
    i (Inclination)                 : 160.77890
    Ω (Longitude of ascending node) : 257.88180
    ω (Argument of perihelion)      : 329.72660
    L (Longitude of perihelion)     : 286.74493
    B (Latitude of perihelion)      : -9.55334
    T (Time of perihelion passage)  : 2460156.85870
    P (Orbital period in years)     : 132011.92

    Epoch                           : 2026 Apr 04
    Reference                       : MPEC 2026-E44

    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
2026-04-04 00:00 UT   10 37 34.5   +30 31 09     8.875    9.572  131.9    4.5   133   22.6 
2026-04-05 00:00 UT   10 37 06.7   +30 31 46     8.894    9.579  130.9    4.5   132   22.6 
2026-04-05 04:18 UT   10 37 01.7   +30 31 52     8.897    9.581  130.8    4.5   132   22.6 
2026-04-06 00:00 UT   10 36 39.3   +30 32 20     8.913    9.587  130.0    4.6   131   22.6 
2026-04-07 00:00 UT   10 36 12.3   +30 32 49     8.932    9.594  129.0    4.6   131   22.6 
2026-04-08 00:00 UT   10 35 45.7   +30 33 15     8.951    9.601  128.1    4.7   130   22.6 
2026-04-09 00:00 UT   10 35 19.5   +30 33 37     8.971    9.608  127.1    4.8   129   22.6 
2026-04-10 00:00 UT   10 34 53.8   +30 33 55     8.990    9.615  126.1    4.8   129   22.6 
2026-04-11 00:00 UT   10 34 28.5   +30 34 09     9.010    9.623  125.2    4.9   128   22.6 
2026-04-12 00:00 UT   10 34 03.7   +30 34 20     9.030    9.630  124.2    4.9   127   22.6 
2026-04-13 00:00 UT   10 33 39.3   +30 34 27     9.051    9.637  123.2    5.0   127   22.7 
2026-04-14 00:00 UT   10 33 15.4   +30 34 30     9.071    9.644  122.3    5.0   126   22.7 
2026-04-15 00:00 UT   10 32 51.9   +30 34 29     9.092    9.651  121.3    5.1   126   22.7 




    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.

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