C/2021 A4 (NEOWISE)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	12 Feb 2021	12.3	1.280 AU	0.433 AU	06h44m	+59°28'	123.8°	39.9°	125°
Perihelion	19 Mar 2021	13.9	1.151 AU	1.147 AU	04h14m	-02°07'	64.5°	51.3°	91°
Today	9 Mar 2026	30.6	14.659 AU	15.431 AU	21h00m	-21°34'	37.7°	2.4°	248°

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 13.0 + 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 C/2021 A4 (NEOWISE) are:

    e (Eccentricity)                : 0.9730240
    q (Perihelion distance)         : 1.1511240
    i (Inclination)                 : 111.68030
    Ω (Longitude of ascending node) : 307.08580
    ω (Argument of perihelion)      : 204.77320
    L (Longitude of perihelion)     : 297.41049
    B (Latitude of perihelion)      : -22.91625
    T (Time of perihelion passage)  : 2459293.31930
    P (Orbital period in years)     : 278.75

    Epoch                           : 2026 Mar 09
    Reference                       : MPEC 2026-E44

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

Ephemerides

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2026-03-08 00:00 UT   20 59 47.6   -21 36 39    15.439   14.649   36.1    2.3   248   30.6 
2026-03-09 00:00 UT   20 59 59.5   -21 35 38    15.434   14.654   37.0    2.3   248   30.6 
2026-03-09 18:17 UT   21 00 08.5   -21 34 52    15.431   14.659   37.7    2.4   248   30.6 
2026-03-10 00:00 UT   21 00 11.3   -21 34 38    15.429   14.660   38.0    2.4   248   30.6 
2026-03-11 00:00 UT   21 00 22.9   -21 33 39    15.424   14.665   38.9    2.4   248   30.6 
2026-03-12 00:00 UT   21 00 34.3   -21 32 40    15.419   14.671   39.9    2.5   248   30.6 
2026-03-13 00:00 UT   21 00 45.6   -21 31 43    15.414   14.676   40.8    2.5   248   30.6 
2026-03-14 00:00 UT   21 00 56.8   -21 30 46    15.408   14.682   41.7    2.6   249   30.6 
2026-03-15 00:00 UT   21 01 07.7   -21 29 51    15.402   14.687   42.7    2.6   249   30.6 
2026-03-16 00:00 UT   21 01 18.5   -21 28 56    15.396   14.693   43.6    2.7   249   30.6 
2026-03-17 00:00 UT   21 01 29.1   -21 28 02    15.390   14.698   44.6    2.7   249   30.6 
2026-03-18 00:00 UT   21 01 39.5   -21 27 09    15.383   14.704   45.5    2.8   249   30.6 
2026-03-19 00:00 UT   21 01 49.7   -21 26 17    15.377   14.709   46.5    2.8   249   30.6 

    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.