Remembering William “John” Cocke 1937 - 2022

On July 4, 2022, at the age of 84, Professor Emeritus William Johnston Cocke III, aka John, “passed on to his next great adventure,” as his family communicated in his obituary. John is survived by Claire, two children Caitlyn and Nathaniel, his brother Stanley H. Cocke, and beloved grandchildren Patrick, Anika, Phobe, and Iris. 

John was graduated from NC State (1959) and earned his Ph.D. in astrophysics from Cornell University in 1964, working under the supervision of Phillip Morrison. He then assisted with the invention of the GPS with the Navy as a civilian contractor in 1966. In August 1968, he accepted a position at Steward Observatory.  He retired 32 years later, beloved by students and notably remembered for leading the team that discovered the optical pulsar in the Crab Nebula in 1968. John was also a self-taught master calligrapher.  

To make a donation in John’s honor, his family would like you to support the next generation of Steward Observatory astronomers by donating to our fund which supports undergraduate, graduate, and post-doctoral fellows.

What is a Pulsar? The first pulsar was discovered by Jocelyn Bell in November of 1967 using a radio telescope.  She noticed some “scruff” on a recording of the telescope output. Further observation determined the scruff was a series of very regular pulses with very accurate spacing between the radio pulses. Following astronomical tradition, they named it a pulsar combing the word pulse with the last two letters of star to make it a pulsar. At first, they named it LGM-1 for “Little Green Men – 1” since the regularity of the pulses hinted at an intelligent origin. The LGM hypothesis was soon abandoned when other pulsars were found at different pulse timings. The idea that pulsars are rotating neutron stars emitting a narrow beam of radiation emerged quickly.

Background: In 1968 many more pulsars were discovered. The primary puzzle was how an astronomical object could turn itself on and off so rapidly. Stars like our sun simply cannot do that which is comforting to know since we depend on the sun for our existence. Attention turned to smaller objects such as white dwarfs and neutron stars. White Dwarfs are the remnants of sun-like stars that have used up their nuclear fuel and then collapse to a star about the size of the earth.  Neutron stars are the remnants of more massive stars which explode in a supernova leaving behind a star made almost entirely of neutrons and with a diameter of roughly 10 to 15 miles, less than the size of Tucson. The collapse concentrates the magnetic field of the original star to extremely high field strengths that can produce two narrow beams of particles and light emanating in opposite directions from the star.  The rotation of the neutron star sweeps the beams in a circle similar to a lighthouse. If the earth happens to be in the path of one of the beams, a quick pulse of radiation will be observed as the beam flashes by.  The idea that something is turning on and off rapidly was incorrect. Instead, the beams are always on but are only briefly seen as they flash by us.

The Discovery: Both John Cocke and Mike Disney had been following the problem of pulsars and the emergence of the neutron star theory. The discovery of a pulsar in the Crab Nebula, a supernova remnant, seemed to strengthen the neutron star theory and they began to wonder if they could see it in visible light instead of radio emission. Most theorists scoffed at the idea but both John and Mike were theorists as well so decided to take a chance and go look. One problem though was that neither of them had ever been to a telescope, let alone used one. On the advice of a colleague, they sought out Don Taylor who had produced exactly the instrument they needed.  The three musketeers took the instrument to the 36” telescope on Kitt Peak where Mike and John learned that it is cold on top of Kitt Peak in January.  They also found the optical flashes from the Crab Nebular pulsar for the first observation of a pulsar in optical light.  Only 5 more optical pulsars have been found in the 50 years since then, but the discovery of optical pulses was a vital piece in solving the mystery of pulsars.

UA News article February 8, 2019, Pulses from a Dead Star, Little Green Men and a Historic Discovery

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