C/2021 D1 (SWAN)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Perihelion	26 Feb 2021	10.8	0.912 AU	1.720 AU	23h24m	+12°44'	24.1°	26.4°	29°
Nearest approach	14 Mar 2021	10.9	0.952 AU	1.679 AU	00h38m	+22°44'	29.7°	31.1°	33°
Today	29 Jun 2026	28.1	16.007 AU	16.276 AU	10h44m	-15°27'	72.9°	3.5°	121°

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 10.0 + 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 D1 (SWAN) are:

    e (Eccentricity)                : 0.9910430
    q (Perihelion distance)         : 0.9115530
    i (Inclination)                 : 31.31780
    Ω (Longitude of ascending node) : 311.05200
    ω (Argument of perihelion)      : 72.61530
    L (Longitude of perihelion)     : 20.92484
    B (Latitude of perihelion)      : 29.73841
    T (Time of perihelion passage)  : 2459272.17050
    P (Orbital period in years)     : 1026.67

    Epoch                           : 2026 May 29
    Reference                       : MPC194173

    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
2026-06-28 00:00 UT   10 44 36.3   -15 28 23    16.247   16.000   74.1    3.5   120   28.1 
2026-06-29 00:00 UT   10 44 43.6   -15 27 56    16.268   16.005   73.3    3.5   121   28.1 
2026-06-29 09:01 UT   10 44 46.4   -15 27 46    16.276   16.007   72.9    3.5   121   28.1 
2026-06-30 00:00 UT   10 44 51.1   -15 27 31    16.288   16.011   72.4    3.5   121   28.1 
2026-07-01 00:00 UT   10 44 58.8   -15 27 07    16.309   16.017   71.6    3.5   121   28.1 
2026-07-02 00:00 UT   10 45 06.6   -15 26 46    16.329   16.022   70.7    3.4   122   28.1 
2026-07-03 00:00 UT   10 45 14.6   -15 26 26    16.349   16.028   69.8    3.4   122   28.1 
2026-07-04 00:00 UT   10 45 22.8   -15 26 08    16.369   16.034   69.0    3.4   123   28.1 
2026-07-05 00:00 UT   10 45 31.2   -15 25 52    16.389   16.039   68.1    3.4   123   28.1 
2026-07-06 00:00 UT   10 45 39.8   -15 25 38    16.409   16.045   67.3    3.4   123   28.1 
2026-07-07 00:00 UT   10 45 48.5   -15 25 26    16.429   16.050   66.4    3.3   124   28.1 
2026-07-08 00:00 UT   10 45 57.4   -15 25 15    16.449   16.056   65.6    3.3   124   28.1 
2026-07-09 00:00 UT   10 46 06.4   -15 25 06    16.468   16.062   64.8    3.3   125   28.2 

    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.