C/2021 A4 (NEOWISE)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	12 Feb 2021	12.2	1.279 AU	0.431 AU	06h44m	+59°24'	123.9°	39.8°	125°
Perihelion	19 Mar 2021	13.9	1.151 AU	1.144 AU	04h14m	-02°11'	64.6°	51.4°	91°
Today	16 Oct 2025	30.1	13.853 AU	13.611 AU	20h36m	-24°26'	102.0°	4.0°	74°

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)                : 0.9729770
    q (Perihelion distance)         : 1.1507450
    i (Inclination)                 : 111.66520
    Ω (Longitude of ascending node) : 307.08740
    ω (Argument of perihelion)      : 204.76260
    L (Longitude of perihelion)     : 297.42299
    B (Latitude of perihelion)      : -22.90908
    T (Time of perihelion passage)  : 2459293.15180
    P (Orbital period in years)     : 277.89

    Epoch                           : 2025 Oct 15
    Reference                       : MPEC 2022-ED3

    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
2025-10-16 00:00 UT   20 36 32.3   -24 27 24    13.596   13.849  102.7    4.0    74   30.1 
2025-10-16 16:17 UT   20 36 28.9   -24 26 59    13.611   13.853  102.0    4.0    74   30.1 
2025-10-17 00:00 UT   20 36 27.4   -24 26 48    13.618   13.855  101.7    4.0    74   30.1 
2025-10-18 00:00 UT   20 36 22.8   -24 26 10    13.641   13.860  100.7    4.1    74   30.1 
2025-10-19 00:00 UT   20 36 18.6   -24 25 32    13.663   13.866   99.7    4.1    74   30.1 
2025-10-20 00:00 UT   20 36 14.7   -24 24 52    13.686   13.872   98.7    4.1    75   30.1 
2025-10-21 00:00 UT   20 36 11.1   -24 24 12    13.709   13.877   97.7    4.1    75   30.1 
2025-10-22 00:00 UT   20 36 07.8   -24 23 30    13.732   13.883   96.7    4.1    75   30.1 
2025-10-23 00:00 UT   20 36 04.9   -24 22 48    13.755   13.889   95.7    4.1    75   30.1 
2025-10-24 00:00 UT   20 36 02.3   -24 22 04    13.777   13.894   94.7    4.1    75   30.1 
2025-10-25 00:00 UT   20 36 00.0   -24 21 19    13.800   13.900   93.7    4.1    75   30.1 
2025-10-26 00:00 UT   20 35 58.1   -24 20 34    13.823   13.906   92.7    4.1    75   30.1 

    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.