C/2020 S3 (Erasmus)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	17 Nov 2020	7.5	0.725 AU	1.038 AU	12h34m	-18°44'	41.8°	65.4°	278°
Perihelion	11 Dec 2020	5.2	0.393 AU	1.287 AU	16h18m	-22°27'	12.8°	33.7°	275°
Today	2 Jul 2025	27.2	14.894 AU	15.028 AU	00h58m	+16°14'	80.5°	3.9°	249°

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.)

The orbital elements of C/2020 S3 (Erasmus) are:

            e (Eccentricity)                : 0.9972220
            q (Perihelion distance)         : 0.3926220
            i (Inclination)                 : 20.06580
            Ω (Longitude of ascending node) : 222.51910
            ω (Argument of perihelion)      : 350.04840
            L (Longitude of perihelion)     : 213.16055
            B (Latitude of perihelion)      : -3.39924
            T (Time of perihelion passage)  : 2459194.87580
            P (Orbital period in years)     : 1680.21

            Epoch                           : 2025 Jun 30
            Reference                       : MPEC 2024-JU4

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

The light curve chart below shows the estimated development of the comet's magnitude. Blue and black dots are visual and photometric CCD observations respectively from COBS or the MPC. The gray curve is based on the absolute magnitude and slope parameter as calculated from the original MPEC, or the latest values provided by the MPC (13.50 + 5 log[∆] + 8.00 log[r]), whereas the red curve is being recalculated every 6 hours based on the available COBS/MPC observations (currently 8.91 + 5 log[∆] + 10.54 log[r]).

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.
A more printer-friendly version of the same chart can be found further down this page as well.

The following chart shows the current location of the comet in a smaller, upside-down telescopic field of view.

A printable version of the short-term path of the comet in a field of view that is optimized for (~10x50) binoculars and finderscopes.

Ephemerides:

Date       Time       RA (2000)    DEC (2000)    delta   radius  elong  phase   PA    magn
2025-07-02 00:00 UT   00 58 26.3   +16 14 57    15.029   14.894   80.4    3.9   249   27.2 
2025-07-02 01:39 UT   00 58 26.5   +16 14 60    15.028   14.894   80.5    3.9   249   27.2 
2025-07-03 00:00 UT   00 58 28.3   +16 15 44    15.018   14.900   81.3    3.9   248   27.2 
2025-07-04 00:00 UT   00 58 30.1   +16 16 30    15.008   14.906   82.3    3.9   248   27.2 
2025-07-05 00:00 UT   00 58 31.6   +16 17 15    14.997   14.912   83.2    3.9   248   27.2 
2025-07-06 00:00 UT   00 58 32.8   +16 17 58    14.987   14.918   84.1    3.9   248   27.2 
2025-07-07 00:00 UT   00 58 33.9   +16 18 40    14.976   14.924   85.1    3.9   248   27.2 
2025-07-08 00:00 UT   00 58 34.6   +16 19 21    14.966   14.930   86.0    3.9   248   27.2 
2025-07-09 00:00 UT   00 58 35.1   +16 19 60    14.955   14.936   86.9    3.9   248   27.2 
2025-07-10 00:00 UT   00 58 35.4   +16 20 37    14.945   14.942   87.9    3.9   247   27.2 
2025-07-11 00:00 UT   00 58 35.4   +16 21 14    14.934   14.948   88.8    3.9   247   27.2 
2025-07-12 00:00 UT   00 58 35.1   +16 21 48    14.923   14.954   89.7    3.9   247   27.2 

    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.