C/2020 S3 (Erasmus)
ephemeris	date	magn	radius	delta	ra	dec	elong	phase	PA
Nearest approach	17 Nov 2020	7.5	0.725 AU	1.037 AU	12h34m	-18°45'	41.9°	65.5°	278°
Perihelion	11 Dec 2020	5.2	0.392 AU	1.286 AU	16h18m	-22°27'	12.8°	33.7°	275°
Today	15 Oct 2025	27.3	15.527 AU	14.550 AU	00h42m	+15°15'	168.2°	0.8°	122°

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 8.9 + 5 log[∆] + 10.5 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/2020 S3 (Erasmus) are:

    e (Eccentricity)                : 0.9972150
    q (Perihelion distance)         : 0.3917850
    i (Inclination)                 : 20.08220
    Ω (Longitude of ascending node) : 222.49370
    ω (Argument of perihelion)      : 350.05060
    L (Longitude of perihelion)     : 213.13818
    B (Latitude of perihelion)      : -3.40116
    T (Time of perihelion passage)  : 2459194.87230
    P (Orbital period in years)     : 1668.53

    Epoch                           : 2025 Oct 14
    Reference                       : MPEC 2024-JU4

    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
2025-10-15 00:00 UT   00 42 47.4   +15 16 39    14.542   15.522  168.7    0.7   126   27.3 
2025-10-15 21:21 UT   00 42 34.8   +15 15 10    14.550   15.527  168.2    0.8   122   27.3 
2025-10-16 00:00 UT   00 42 33.2   +15 14 59    14.550   15.528  168.1    0.8   122   27.3 
2025-10-17 00:00 UT   00 42 19.0   +15 13 18    14.559   15.534  167.5    0.8   118   27.3 
2025-10-18 00:00 UT   00 42 04.9   +15 11 37    14.567   15.540  166.8    0.8   114   27.3 
2025-10-19 00:00 UT   00 41 50.9   +15 09 55    14.576   15.546  166.1    0.9   111   27.3 
2025-10-20 00:00 UT   00 41 37.0   +15 08 13    14.586   15.552  165.3    0.9   108   27.3 
2025-10-21 00:00 UT   00 41 23.1   +15 06 31    14.595   15.558  164.5    1.0   105   27.3 
2025-10-22 00:00 UT   00 41 09.4   +15 04 49    14.605   15.563  163.7    1.0   103   27.3 
2025-10-23 00:00 UT   00 40 55.8   +15 03 07    14.615   15.569  162.9    1.1   101   27.3 
2025-10-24 00:00 UT   00 40 42.2   +15 01 24    14.626   15.575  162.0    1.1    99   27.3 
2025-10-25 00:00 UT   00 40 28.8   +14 59 42    14.637   15.581  161.1    1.2    97   27.3 

    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.