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	12 Dec 2025	27.0	14.253 AU	14.317 AU	11h34m	-04°22'	84.3°	3.9°	293°

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)                : 0.8903270
    q (Perihelion distance)         : 3.6412010
    i (Inclination)                 : 114.98290
    Ω (Longitude of ascending node) : 354.92390
    ω (Argument of perihelion)      : 61.80710
    L (Longitude of perihelion)     : 316.68898
    B (Latitude of perihelion)      : 53.02484
    T (Time of perihelion passage)  : 2458890.56580
    P (Orbital period in years)     : 191.30

    Epoch                           : 2025 Nov 12
    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
2025-12-11 00:00 UT   11 34 06.0   -04 21 25    14.332   14.247   83.1    3.9   293   27.0 
2025-12-12 00:00 UT   11 34 04.4   -04 22 30    14.319   14.252   84.1    3.9   293   27.0 
2025-12-12 04:08 UT   11 34 04.0   -04 22 42    14.317   14.253   84.3    3.9   293   27.0 
2025-12-13 00:00 UT   11 34 02.4   -04 23 34    14.307   14.257   85.1    3.9   293   27.0 
2025-12-14 00:00 UT   11 34 00.2   -04 24 37    14.294   14.262   86.1    3.9   293   27.0 
2025-12-15 00:00 UT   11 33 57.7   -04 25 38    14.281   14.266   87.1    4.0   293   27.0 
2025-12-16 00:00 UT   11 33 54.9   -04 26 37    14.269   14.271   88.1    4.0   293   27.0 
2025-12-17 00:00 UT   11 33 51.8   -04 27 34    14.256   14.276   89.2    4.0   293   27.0 
2025-12-18 00:00 UT   11 33 48.5   -04 28 30    14.243   14.281   90.2    4.0   293   27.0 
2025-12-19 00:00 UT   11 33 44.9   -04 29 24    14.231   14.285   91.2    3.9   294   27.0 
2025-12-20 00:00 UT   11 33 41.0   -04 30 17    14.218   14.290   92.2    3.9   294   27.0 
2025-12-21 00:00 UT   11 33 36.8   -04 31 08    14.205   14.295   93.2    3.9   294   27.0 
2025-12-22 00:00 UT   11 33 32.4   -04 31 57    14.192   14.300   94.3    3.9   294   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.