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C/2021 T4 (Lemmon)
ephemeris date magn radius delta ra dec elong phase PA
Nearest approach20 Jul 20238.51.488 AU0.538 AU 19h58m-56°02'144.7°23.3°359°
Perihelion31 Jul 20239.01.480 AU0.669 AU 16h25m-43°30'121.7°35.7°86°
Today9 Oct 202623.710.898 AU11.584 AU 10h51m+25°58'44.7°3.7°312°
C/2021 T4 (Lemmon)- 2026-10-09
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)                : 0.9992350
    q (Perihelion distance)         : 1.4801290
    i (Inclination)                 : 160.77970
    Ω (Longitude of ascending node) : 257.87310
    ω (Argument of perihelion)      : 329.70070
    L (Longitude of perihelion)     : 286.76149
    B (Latitude of perihelion)      : -9.56042
    T (Time of perihelion passage)  : 2460156.62550
    P (Orbital period in years)     : 85105.42

    Epoch                           : 2026 Oct 09
    Reference                       : MPC194177

    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
2026-10-08 00:00 UT   10 51 20.3   +25 59 04    11.592   10.886   43.2    3.6   313   23.7 
2026-10-09 00:00 UT   10 51 33.8   +25 58 49    11.588   10.893   44.1    3.7   312   23.7 
2026-10-09 18:02 UT   10 51 43.9   +25 58 39    11.584   10.898   44.7    3.7   312   23.7 
2026-10-10 00:00 UT   10 51 47.2   +25 58 36    11.583   10.900   45.0    3.7   312   23.7 
2026-10-11 00:00 UT   10 52 00.3   +25 58 27    11.578   10.906   45.8    3.8   311   23.7 
2026-10-12 00:00 UT   10 52 13.3   +25 58 19    11.574   10.913   46.7    3.8   311   23.7 
2026-10-13 00:00 UT   10 52 26.0   +25 58 14    11.568   10.920   47.5    3.9   310   23.7 
2026-10-14 00:00 UT   10 52 38.5   +25 58 11    11.563   10.927   48.4    3.9   310   23.7 
2026-10-15 00:00 UT   10 52 50.8   +25 58 11    11.558   10.934   49.3    4.0   309   23.7 
2026-10-16 00:00 UT   10 53 02.9   +25 58 13    11.552   10.941   50.2    4.0   309   23.7 
2026-10-17 00:00 UT   10 53 14.8   +25 58 18    11.546   10.947   51.0    4.1   308   23.7 
2026-10-18 00:00 UT   10 53 26.4   +25 58 26    11.540   10.954   51.9    4.1   308   23.7 
2026-10-19 00:00 UT   10 53 37.8   +25 58 35    11.534   10.961   52.8    4.2   307   23.7 




    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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