C/2021 Y1 (ATLAS)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	12 Dec 2022	14.2	2.614 AU	1.691 AU	03h59m	+05°44'	154.5°	9.3°	45°
Perihelion	1 May 2023	13.8	2.032 AU	2.515 AU	04h43m	-24°12'	50.7°	22.6°	137°
Today	23 Apr 2026	24.2	10.019 AU	9.223 AU	16h45m	-09°16'	140.4°	3.7°	261°

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 8.5 + 5 log[∆] + 10.9 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/2021 Y1 (ATLAS) are:

    e (Eccentricity)                : 1.0017940
    q (Perihelion distance)         : 2.0322930
    i (Inclination)                 : 77.16290
    Ω (Longitude of ascending node) : 244.76260
    ω (Argument of perihelion)      : 245.85810
    L (Longitude of perihelion)     : 271.13097
    B (Latitude of perihelion)      : -62.83898
    T (Time of perihelion passage)  : 2460065.61750

    Epoch                           : 2026 Apr 23
    Reference                       : MPEC 2026-E44

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-04-22 00:00 UT   16 46 01.3   -09 21 34     9.230   10.006  138.5    3.8   262   24.2 
2026-04-23 00:00 UT   16 45 43.4   -09 18 51     9.226   10.013  139.5    3.7   262   24.2 
2026-04-23 21:32 UT   16 45 27.1   -09 16 24     9.223   10.019  140.4    3.7   261   24.2 
2026-04-24 00:00 UT   16 45 25.2   -09 16 08     9.223   10.020  140.5    3.7   261   24.2 
2026-04-25 00:00 UT   16 45 06.7   -09 13 25     9.219   10.026  141.5    3.6   261   24.2 
2026-04-26 00:00 UT   16 44 48.0   -09 10 43     9.216   10.033  142.5    3.5   260   24.2 
2026-04-27 00:00 UT   16 44 29.0   -09 08 02     9.214   10.040  143.4    3.4   259   24.2 
2026-04-28 00:00 UT   16 44 09.7   -09 05 21     9.211   10.047  144.4    3.3   259   24.2 
2026-04-29 00:00 UT   16 43 50.1   -09 02 41     9.209   10.054  145.4    3.3   258   24.2 
2026-04-30 00:00 UT   16 43 30.4   -09 00 02     9.207   10.061  146.3    3.2   257   24.2 
2026-05-01 00:00 UT   16 43 10.3   -08 57 23     9.205   10.068  147.3    3.1   256   24.2 
2026-05-02 00:00 UT   16 42 50.1   -08 54 45     9.204   10.075  148.2    3.0   255   24.2 
2026-05-03 00:00 UT   16 42 29.6   -08 52 07     9.202   10.081  149.2    2.9   255   24.2 

    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.