C/2017 M4 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	17 Jan 2019	14.0	3.233 AU	3.954 AU	17h20m	-13°10'	37.8°	10.7°	287°
Nearest approach	13 May 2019	13.3	3.418 AU	2.466 AU	16h00m	-40°11'	156.6°	6.7°	336°
Today	27 Dec 2025	26.2	17.790 AU	17.307 AU	06h09m	-38°33'	118.0°	2.8°	4°

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 4.8 + 5 log[∆] + 12.1 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 M4 (ATLAS) are:

    e (Eccentricity)                : 0.9999550
    q (Perihelion distance)         : 3.2326860
    i (Inclination)                 : 105.63600
    Ω (Longitude of ascending node) : 65.99360
    ω (Argument of perihelion)      : 167.36450
    L (Longitude of perihelion)     : 69.45128
    B (Latitude of perihelion)      : 12.16061
    T (Time of perihelion passage)  : 2458500.95030

    Epoch                           : 2025 Dec 26
    Reference                       : MPEC 2022-OB6

    Classification(s):              : Nearly isotropic; New (a > 10000 AU)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-12-26 00:00 UT   06 09 32.2   -38 34 57    17.298   17.781  118.0    2.8     2   26.2 
2025-12-27 00:00 UT   06 09 13.2   -38 34 19    17.303   17.787  118.0    2.8     3   26.2 
2025-12-27 16:10 UT   06 09 00.4   -38 33 51    17.307   17.790  118.0    2.8     4   26.2 
2025-12-28 00:00 UT   06 08 54.2   -38 33 37    17.308   17.792  118.0    2.8     5   26.2 
2025-12-29 00:00 UT   06 08 35.3   -38 32 52    17.314   17.797  118.0    2.8     6   26.2 
2025-12-30 00:00 UT   06 08 16.5   -38 32 03    17.320   17.802  118.0    2.8     7   26.2 
2025-12-31 00:00 UT   06 07 57.6   -38 31 11    17.326   17.808  117.9    2.8     8   26.2 
2026-01-01 00:00 UT   06 07 38.9   -38 30 16    17.332   17.813  117.9    2.8    10   26.2 
2026-01-02 00:00 UT   06 07 20.2   -38 29 17    17.338   17.818  117.8    2.8    11   26.2 
2026-01-03 00:00 UT   06 07 01.6   -38 28 15    17.344   17.823  117.7    2.8    12   26.2 
2026-01-04 00:00 UT   06 06 43.1   -38 27 10    17.351   17.828  117.6    2.8    13   26.2 
2026-01-05 00:00 UT   06 06 24.7   -38 26 02    17.357   17.834  117.5    2.8    14   26.2 
2026-01-06 00:00 UT   06 06 06.3   -38 24 51    17.364   17.839  117.4    2.8    16   26.2 

    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.