C/2017 T3 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	19 Jul 2018	9.1	0.821 AU	1.418 AU	06h44m	-09°11'	34.7°	44.8°	210°
Nearest approach	1 Aug 2018	9.2	0.858 AU	1.347 AU	08h08m	-20°29'	39.6°	48.9°	195°
Today	7 Dec 2025	29.5	20.498 AU	21.163 AU	16h05m	+22°10'	46.5°	2.0°	344°

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 9.3 + 5 log[∆] + 10.4 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/2017 T3 (ATLAS) are:

    e (Eccentricity)                : 0.9993860
    q (Perihelion distance)         : 0.8213790
    i (Inclination)                 : 88.29950
    Ω (Longitude of ascending node) : 230.26570
    ω (Argument of perihelion)      : 246.77190
    L (Longitude of perihelion)     : 234.22102
    B (Latitude of perihelion)      : -66.71318
    T (Time of perihelion passage)  : 2458319.25380
    P (Orbital period in years)     : 48928.61

    Epoch                           : 2023 Sep 24
    Reference                       : MPC114600

    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
2025-12-06 00:00 UT   16 05 11.6   +22 10 09    21.162   20.489   45.9    2.0   346   29.5 
2025-12-07 00:00 UT   16 05 23.6   +22 10 20    21.163   20.495   46.3    2.0   344   29.5 
2025-12-07 15:13 UT   16 05 31.1   +22 10 28    21.163   20.498   46.5    2.0   344   29.5 
2025-12-08 00:00 UT   16 05 35.5   +22 10 33    21.163   20.500   46.6    2.0   343   29.5 
2025-12-09 00:00 UT   16 05 47.4   +22 10 48    21.163   20.505   47.0    2.0   342   29.5 
2025-12-10 00:00 UT   16 05 59.3   +22 11 05    21.163   20.510   47.4    2.0   341   29.5 
2025-12-11 00:00 UT   16 06 11.1   +22 11 25    21.163   20.515   47.9    2.0   340   29.5 
2025-12-12 00:00 UT   16 06 22.8   +22 11 46    21.162   20.521   48.3    2.1   338   29.5 
2025-12-13 00:00 UT   16 06 34.5   +22 12 09    21.161   20.526   48.7    2.1   337   29.5 
2025-12-14 00:00 UT   16 06 46.2   +22 12 34    21.160   20.531   49.2    2.1   336   29.5 
2025-12-15 00:00 UT   16 06 57.7   +22 13 02    21.159   20.536   49.7    2.1   335   29.5 
2025-12-16 00:00 UT   16 07 09.2   +22 13 31    21.158   20.542   50.1    2.1   334   29.5 
2025-12-17 00:00 UT   16 07 20.7   +22 14 02    21.157   20.547   50.6    2.1   333   29.5 

    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.