C/2004 F4 (Bradfield)

Lore & Background

The comet was discovered by amateur astronomer William A. Bradfield from Yankalilla, South Australia on 23 March 2004 with a 0.25-m reflector telescope, during his search for sungrazing comets. That was Bradfield's 18th comet discovery. The comet was then located in evening twilight and its magnitude was estimated to be about magnitude 8. Robert H. McNaught observed the comet on 9 April 2004 and estimated that the comet had a magnitude of 5, while Terry Lovejoy estimated its magnitude to be 3.3 on 12 April, while its tail measured half a degree long. At that time, two more naked eye comets were visible in the sky, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR).

The comet reached perihelion on 17 April 2004, at a distance of 0.168 AU. It became visible in the C3 coronograph of the Solar and Heliospheric Observatory (SOHO) between 16 and 20 April 2004. The comet had a bright head and a long white tail. The appearance of the comet in the coronograph was unusual, with the coma growing perpendicularly to the apparent motion, indicating a growing dust tail, while on 19 April a series of structures were seen near the head, probably streamers or striae. If these were streamers, they indicated an uprise in activity every 0.5 day. The orbital ephemeris based on the SOHO observations indicated that the comet on 20 April had a magnitude of 2.5.

The comet was spotted in bright twilight on 22 April, when the comet had an estimated magnitude of about 4 to 4.5. On 25 April, while the comet was estimated to have a same magnitude, its tail was estimated to 8.5 degrees long with naked eye, while on 27 April the tail length was estimated to be 10 degrees with 7×35 binoculars, while the comet was estimated to have a magnitude of 5. On 30 April the apparent magnitude was estimated to be 5.8 while the tail was estimated to be 3.5 degrees long. On 2–3 May, Earth crossed the orbital plane of the comet, resulting in a sunward spike (or anti-tail) and a ray-shaped structure in the dust tail.

Reader's Guide

C/2004 F4 (Bradfield) is significant as the 18th comet discovery by prolific amateur astronomer William A. Bradfield, underscoring the ongoing contributions of amateurs to comet hunting. Its peak brightness of about magnitude 3.3 made it a naked-eye object, and it was one of three such comets visible simultaneously in April 2004, alongside C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), offering a rare triple-comet spectacle. The comet's observation by the SOHO coronograph between 16 and 20 April 2004 provided detailed data on its unusual coma behavior, including a growing dust tail perpendicular to motion and possible streamers indicating activity cycles of about 0.5 day. Post-perihelion, the comet displayed a long tail reaching up to 10 degrees in length as seen through binoculars, and Earth's crossing of its orbital plane on 2–3 May produced a sunward spike (anti-tail) and ray-shaped dust tail structures. These features, documented by amateur and professional observers, contribute to understanding cometary dust evolution and orbital dynamics.

Did You Know?

• It was one of three naked-eye comets visible simultaneously in April 2004.
• The comet's tail was estimated to be 10 degrees long on 27 April 2004 when viewed with 7×35 binoculars.
• Earth crossed the comet's orbital plane on 2–3 May 2004, producing a sunward spike (anti-tail).