A/2019 O4
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	5 Sep 2019	21.1	3.879 AU	3.037 AU	21h41m	+26°59'	141.7°	9.3°	149°
Perihelion	11 Feb 2020	21.7	3.641 AU	4.306 AU	20h29m	+25°06'	42.6°	10.6°	336°
Today	29 Oct 2025	27.0	14.043 AU	14.775 AU	11h31m	-03°14'	41.1°	2.7°	287°

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. The displayed light curve is calculated under the assumption that the object remains inactive. (H=15.10; G=.15).

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 A/2019 O4 are:

    e (Eccentricity)                : 0.8903370
    q (Perihelion distance)         : 3.6413070
    i (Inclination)                 : 114.98530
    Ω (Longitude of ascending node) : 354.92420
    ω (Argument of perihelion)      : 61.80900
    L (Longitude of perihelion)     : 316.68456
    B (Latitude of perihelion)      : 53.02471
    T (Time of perihelion passage)  : 2458890.58260
    P (Orbital period in years)     : 191.34

    Epoch                           : 2025 Oct 28
    Reference                       : MPEC 2021-P47

    Classification(s):              : Nearly isotropic; Returning (a < 10000 AU); Halley type (P < 200 years)

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-10-28 00:00 UT   11 31 18.2   -03 12 03    14.782   14.037   40.1    2.6   286   27.0 
2025-10-29 00:00 UT   11 31 26.5   -03 13 58    14.776   14.042   41.1    2.7   287   27.0 
2025-10-29 01:16 UT   11 31 26.9   -03 14 05    14.775   14.043   41.1    2.7   287   27.0 
2025-10-30 00:00 UT   11 31 34.6   -03 15 54    14.769   14.047   42.0    2.7   287   27.0 
2025-10-31 00:00 UT   11 31 42.6   -03 17 48    14.762   14.052   43.0    2.8   287   27.0 
2025-11-01 00:00 UT   11 31 50.4   -03 19 42    14.754   14.057   43.9    2.8   287   27.0 
2025-11-02 00:00 UT   11 31 58.0   -03 21 35    14.747   14.061   44.9    2.9   287   27.0 
2025-11-03 00:00 UT   11 32 05.4   -03 23 27    14.739   14.066   45.8    2.9   288   27.0 
2025-11-04 00:00 UT   11 32 12.6   -03 25 19    14.731   14.071   46.8    2.9   288   27.0 
2025-11-05 00:00 UT   11 32 19.7   -03 27 09    14.723   14.076   47.7    3.0   288   27.0 
2025-11-06 00:00 UT   11 32 26.5   -03 28 59    14.715   14.081   48.7    3.0   288   27.0 
2025-11-07 00:00 UT   11 32 33.2   -03 30 48    14.706   14.085   49.6    3.1   288   27.0 
2025-11-08 00:00 UT   11 32 39.7   -03 32 36    14.698   14.090   50.6    3.1   288   27.0 

    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.