William Ashley Bradfield (20 June 1927 – 9 June 2014) was a New Zealand-born Australian amateur astronomer, notable as a prolific amateur discoverer of comets. He discovered 18 comets, all of which bear his name as the sole discoverer.

His astronomical achievements were summed up by Brian G. Marsden, director emeritus of the IAU's Central Bureau for Astronomical Telegrams: "To discover 18 comets visually is an extraordinary accomplishment in any era, but to do so now is truly remarkable, and I think we can be pretty sure nobody will be able to do it again. And it's all the more astounding that in no case did he have to share a discovery with some other independent discoverer. More than any other recipient, Bill Bradfield outstandingly deserves the Edgar Wilson Award."

Biography Bradfield was born in Levin, New Zealand on 20 June 1927. He grew up on a dairy farm, where his interests in rocketry and astronomy first developed, and when he was 15 he got his first small telescope. He attended the University of New Zealand, where he graduated with a bachelor's degree in Mechanical Engineering. He spent 2 years in England doing a rocket propulsion residency and then in 1953 he moved to Australia, taking up residence in Adelaide, where he worked for the Australian Department of Defence as a rocket propulsion engineer and research scientist until he retired in 1986. This was also where he met Eileen; they were married in 1957, and they went on to have three daughters.

Bradfield joined the Astronomical Society of South Australia (ASSA) in 1970 which fueled his interest, and he started hunting for comets in 1971, using a second-hand telescope which he bought from another ASSA member.

Just over a year and 260 hours of searching later, he was rewarded with finding Comet Bradfield (C/1972 E1). Six comets followed in his first six years, and in 1987 the discovery of his 13th comet made him the most prolific comet-hunter of the 20th century. Eventually his count built to 18 comets after 3500 hours of searching, with the 18th and final comet discovery coming on 23 March 2004 when he was 76 years old.

When Bradfield discovered a comet and communicated it to the International Astronomical Union (IAU), it kicked off worldwide action. Within 14 hours of reporting his 17th comet in 1995, it had been observed by more than 20 observers, including the European Southern Observatory (ESO) 1-meter Schmidt telescope at La Silla, Chile.

His discoveries were particularly notable because he worked alone to discover them, using old and home-made telescopic equipment. Apart from the 100-year-old lens and modern eyepieces, the remainder of his telescope was homemade, but perfectly suited for hunting comets. He did not use photographic or computerized detection equipment, relying instead on purely visual sweeping across the skies.

Having joined the Astronomical Society of South Australia (ASSA) in 1970, Bradfield served as its President from 1977 to 1979. In 1989 he was appointed an honorary Life Member, and he was inducted into the ASSA Hall of Fame in 2013.

He died on 9 June 2014 after a long illness, at age 86.

Awards and honors Asteroid 3430 Bradfield was named in his honour. Bradfield received the Berenice and Arthur Page Medal from the Astronomical Society of Australia in 1981. He was made a member of the Order of Australia (AM) "in recognition of his service to astronomy" in 1989. He was made an Honorary Life Member of the Astronomical Society of South Australia in 1989. In 2000 the Astronomical Society of South Australia created the Bill Bradfield Astronomy Award in honour of his achievements, given to an amateur who displays exceeding accomplishment in a given year in the field of astronomy. He was awarded the Edgar Wilson Award from the Smithsonian Astrophysical Observatory (SAO) through the IAU's Central Bureau for Astronomical Telegrams (CBAT) in 2004. In 2013 he was inducted into the ASSA Hall of Fame.

List of discovered comets Number Comet Hours Date Mag 1 C/1972 E1 260 Mar 12.81 10 2 C/1974 C1 306 Feb 12.49 9 3 C/1975 E1 145 Mar 12.45 9 4 C/1975 V2 106 Nov 11.74 10 5 C/1976 D1 57 Feb 19.49 9 6 C/1976 E1 9 Mar 3.778 9 7 C/1978 C1 360 Feb 4.755 8 8 C/1978 T3 75 Oct 10.785 9 9 C/1979 M1 98 Jun 24.417 10 10 C/1979 Y1 67 Dec 24.753 5 11 C/1980 Y1 113 Dec 17.751 6 12 P/1984 A1 384 Jan 7.733 11 13 C/1987 P1 307 Aug 11.437 10 14 C/1989 A3 164 Jan 6.514 12 15 C/1992 B1 129 Jan 31.736 10 16 C/1992 J2 30 May 3.806 10 17 C/1995 Q1 289 Aug 17.410 6 18 C/2004 F4 Mar 23.43 8

Comet: Initial designation of the comet Hours: Number of search hours for discovery Date: Discovery date in UT Mag: Total magnitude (brightness) of comet at discovery

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