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	27 Oct 2025	29.5	20.282 AU	20.978 AU	15h57m	+22°28'	44.5°	2.0°	40°

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
2025-10-26 00:00 UT   15 57 03.4   +22 30 01    20.965   20.274   44.9    2.0    42   29.5 
2025-10-27 00:00 UT   15 57 14.4   +22 28 57    20.974   20.279   44.6    2.0    41   29.5 
2025-10-27 12:31 UT   15 57 20.2   +22 28 24    20.978   20.282   44.5    2.0    40   29.5 
2025-10-28 00:00 UT   15 57 25.5   +22 27 54    20.982   20.284   44.3    2.0    40   29.5 
2025-10-29 00:00 UT   15 57 36.6   +22 26 53    20.991   20.290   44.1    2.0    38   29.5 
2025-10-30 00:00 UT   15 57 47.9   +22 25 53    20.999   20.295   43.8    1.9    37   29.5 
2025-10-31 00:00 UT   15 57 59.2   +22 24 55    21.007   20.300   43.6    1.9    36   29.5 
2025-11-01 00:00 UT   15 58 10.5   +22 23 59    21.015   20.305   43.3    1.9    34   29.5 
2025-11-02 00:00 UT   15 58 22.0   +22 23 04    21.023   20.311   43.1    1.9    33   29.5 
2025-11-03 00:00 UT   15 58 33.5   +22 22 11    21.031   20.316   42.9    1.9    31   29.5 
2025-11-04 00:00 UT   15 58 45.1   +22 21 19    21.038   20.321   42.7    1.9    30   29.5 
2025-11-05 00:00 UT   15 58 56.7   +22 20 30    21.045   20.326   42.6    1.9    29   29.5 
2025-11-06 00:00 UT   15 59 08.4   +22 19 42    21.052   20.332   42.4    1.9    27   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.