P/2021 J3 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	15 May 2019	16.8	4.884 AU	3.904 AU	15h33m	-03°01'	164.2°	3.2°	187°
Perihelion	29 Jun 2019	17.0	4.878 AU	4.175 AU	15h17m	-03°54'	128.9°	9.3°	117°
Today	8 Aug 2026	22.4	10.828 AU	10.395 AU	01h42m	-05°33'	112.8°	5.0°	255°

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 light curve is based on the absolute magnitude and slope parameter as calculated from an MPEC, or the latest values provided by the minor planet center. (7.0 + 5 log[∆] + 10.0 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 P/2021 J3 (ATLAS) are:

    e (Eccentricity)                : 0.4502060
    q (Perihelion distance)         : 4.8781100
    i (Inclination)                 : 14.50950
    Ω (Longitude of ascending node) : 110.85670
    ω (Argument of perihelion)      : 125.52030
    L (Longitude of perihelion)     : 57.25971
    B (Latitude of perihelion)      : 11.76613
    T (Time of perihelion passage)  : 2458664.39420
    P (Orbital period in years)     : 26.43

    Epoch                           : 2026 Aug 07
    Reference                       : MPC194174

    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
2026-08-07 00:00 UT   01 42 38.1   -05 31 48    10.411   10.826  111.6    5.0   254   22.4 
2026-08-08 00:00 UT   01 42 36.7   -05 33 22    10.398   10.828  112.6    5.0   255   22.4 
2026-08-08 05:21 UT   01 42 36.4   -05 33 43    10.395   10.828  112.8    5.0   255   22.4 
2026-08-09 00:00 UT   01 42 35.0   -05 34 57    10.385   10.830  113.5    4.9   255   22.4 
2026-08-10 00:00 UT   01 42 33.0   -05 36 34    10.373   10.832  114.4    4.9   255   22.4 
2026-08-11 00:00 UT   01 42 30.6   -05 38 13    10.360   10.834  115.4    4.8   256   22.4 
2026-08-12 00:00 UT   01 42 27.9   -05 39 53    10.348   10.835  116.3    4.8   256   22.4 
2026-08-13 00:00 UT   01 42 24.8   -05 41 34    10.336   10.837  117.3    4.8   256   22.4 
2026-08-14 00:00 UT   01 42 21.4   -05 43 17    10.324   10.839  118.2    4.7   257   22.4 
2026-08-15 00:00 UT   01 42 17.6   -05 45 02    10.312   10.841  119.1    4.7   257   22.4 
2026-08-16 00:00 UT   01 42 13.5   -05 46 48    10.300   10.843  120.1    4.6   257   22.4 
2026-08-17 00:00 UT   01 42 09.1   -05 48 35    10.288   10.845  121.0    4.6   258   22.4 
2026-08-18 00:00 UT   01 42 04.4   -05 50 23    10.277   10.847  122.0    4.5   258   22.4 

    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.