Home=Current Comets: C/2025 R3
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On Sep. 8, 2025, the PANSTARRS team discovered an additional comet, this time in the constellation Andromeda. Comet C/2025 R3 (PANSTARRS) showed a condensed 5" coma of total magnitude 19.5 and a broad 10" tail in p.a. 165-225°. The comet will pass perihelion at a solar distance of 0.50 AU on Apr. 19, 2026, expected to peak at 9 mag if it shows an average development (CBET 5607). It is expected to be brighter than 16 mag between February and June 2026. During this period it will move through the constellations Pegasus, Pisces (perihelion), Cetus, Taurus, Eridanus, Orion, Monoceros, and Canis Major. From Central European locations the comet can only be observed in the evening sky until mid-February 2026 and just above the eastern horizon in the morning sky between early March and mid-April. However, the absolute magnitude, as derived from published observations, is 2 mag below the Bortle-limit. Thus there is a certain probability that the comet will disintegrate on its way to the Sun. If the comet survives its perihelion without major damage, J. Marcus' formulae predict that there will be significant forward scattering in the second half of April, which could increase its brightness by up to 6.5 mag on Apr. 26! However, the comet will only be 5° from the Sun on that day. Earth will cross the comet's orbital plane on Apr. 29.
Despite its rather low absolute magnitude the comet appears to have survived its small perihelion distance. At least, that is what post-perihelion observations indicate so far and the comet's brightness trend suggests. Based on 295 observations from 73 observers (until the opening of May 2026) a very steady brightness trend is evident, which - outside the 10 days immediately following perihelion - can be well represented by the parameters
m0 = 8.4 mag / n = 4.6This results in a maximum brightness of 3.5 mag on Apr. 26, 2026. During the first 10 days after perihelion the comet could only be observed by satellites (primarily SOHO and CCOR). The values derived from these observations indicate a maximum brightness of 1.5 mag, due to forward scattering. This brightening, caused by dust particles, resulted in an short-lived increase of 2.0 mag. This remained below the theoretical maximum value (6.5 mag), as the comet contained only a small amount of dust. By May 10 the comet had faded to 6.0 mag.
Total Brightness and Coma Diameter
The apparent coma diameter remained fairly constant at short of 1' at the start of the apparition. From mid-March onward it increased significantly, reaching a maximum of 9' around Apr. 20, 2026. By around May 10 it appears to have decreased again to 6'. The absolute coma diameter measured 150,000 km at the start of the apparition, then, starting in mid-March, it increased significantly, reaching a maximum of 325,000 km in early April 2026. By around May 10 it had shrunk to 225,000 km. At the start of the apparition the coma appeared quite diffuse (DC 3), but, starting in mid-March, it rapidly condensed, reaching a maximum of DC 7–8 around April 15. Post-perihelion the degree of condensation decreased from DC 7 to DC 5–6 by May 10. A tail was first reported around March 20. It reached a visual length of 4° (9 mio. km) around perihelion. The position angle of the tail decreased from 320° to 280° between mid-March and April 20. Post-perihelion it has remained constant at 130° so far.Post-perihelion the comet should exhibit an interesting tail morphology for several days, as shown in the following diagram.
Simulation of the Tail Development
Andreas Kammerer
