John Randolph "Jack" Winckler was a trailblazing experimental physicist whose work transformed our understanding of cosmic rays, auroras, solar flares, and the Earth's magnetosphere. He was born on October 27, 1916, in North Plainfield, New Jersey. His childhood, surrounded by music, craftsmanship, and a love for the natural world, fostered a curiosity that would later shape his scientific career. Although economic hardships of the Great Depression delayed his higher education, Winckler worked from 1937 to 1942 as a research physicist at the Johns-Manville Corporation. Encouraged by mentors there, he pursued formal studies and earned a Bachelor of Science degree from Rutgers University in 1942.

Continuing his education, Winckler completed a Ph.D. in physics at Princeton University in 1946 under the supervision of Rudolf W. Ladenburg. During his graduate studies, he also contributed to the U.S. Office of Research and Development, applying his expertise to wartime research in supersonic airflow. Following his doctorate, he served as an instructor at Princeton's Palmer Laboratory from 1946 to 1949. At Princeton, he crossed paths with notable figures such as Eugene Wigner, further shaping his scientific outlook.

In 1949, Winckler joined the University of Minnesota as an assistant professor, where he remained for his entire career, advancing to full professor and later becoming emeritus professor upon his retirement in 1986. His colleagues at Minnesota included renowned physicists such as Edward P. Ney, Alfred O. Nier, John T. Tate, and John H. Williams. During his tenure, he advised numerous students, including Kinsey A. Anderson, and developed a vibrant research program in solar, magnetospheric, auroral, and atmospheric physics.

Winckler's groundbreaking work with high-altitude balloons stands as a central legacy of his career. Building upon his early adaptations of U.S. Navy sonar technology for cosmic ray research, he pioneered balloon-borne cosmic ray measurements in the late 1940s, culminating in an ambitious latitude survey aboard the USS Norton Sound. His careful design of cosmic ray "telescopes" -intricate arrays of Geiger-Mueller counters- provided the most reliable data of that era and demonstrated the urgent need for more sophisticated instruments in cosmic ray studies.

At the University of Minnesota, he played a key role in the classified effort from 1951 to 1956 to improve high-altitude balloon technology, contributing to safer and more reliable balloon flights for both scientific and military purposes. His improvements in balloon design, coupled with his careful management of hundreds of balloon launches, helped establish high-altitude research as a robust experimental platform?.

The International Geophysical Year (1957-1958) offered Winckler an opportunity to make some of his most celebrated discoveries. On July 1, 1957, he launched a balloon over Minneapolis that unexpectedly recorded intense X-rays associated with a brilliant aurora. This observation revealed that auroral displays were tied to energetic electrons colliding with the atmosphere, advancing the emerging understanding of magnetospheric physics. He also detected X-rays and gamma rays from solar flares, providing the first direct evidence that high-energy solar events produced bursts of photons, a discovery that opened a new frontier in solar astrophysics?.

Winckler's contributions to space science extended into the satellite era. His instruments flew on spacecraft such as ATS-1, where his work revealed the connection between intensifications of the aurora and enhancements of energetic electrons at geostationary orbit, leading to the concept of the magnetospheric substorm. His fascination with active experimentation culminated in the "ECHO" project: from 1970 to 1988, Winckler and his team injected beams of electrons into space using sounding rockets to probe the magnetosphere, validating theories about particle motion along magnetic field lines and mapping electric fields?.

Even after retiring from formal teaching, Winckler's passion for discovery remained undiminished. At the O'Brien Observatory, he developed the Skyflash program to monitor rapid auroral variations and ultimately achieved the first confirmed visual documentation of "sprites"-gigantic lightning discharges extending from thunderstorms into the upper atmosphere?. His modest, cost-effective approach to this discovery, contrasted with the million-dollar projects it inspired, is a testament to his ingenuity and relentless curiosity.

Over the course of his career, Winckler was the author of more than 145 scientific papers and was honored with numerous accolades, including the American Institute for Aviation and Astronautics Space Science Award (1962), a Guggenheim Fellowship at Meudon Observatory (1965-1966), a Fulbright Fellowship at Paul Sabatier University (1985), the Arctowski Medal from the National Academy of Sciences (1978), the Soviet Geophysical Committee's International Geophysical Year Commemorative Medal (1985), and the NASA Medal for Exceptional Scientific Achievement (1991). In 1996, he was elected to the U.S. National Academy of Sciences?.

Winckler's personal life was equally rich. He married concert pianist Louise McDowell in 1943, and together they raised four daughters and one son. A passionate outdoorsman, he often sought dark skies in the Boundary Waters Canoe Area Wilderness to photograph the aurora, merging his scientific pursuits with a lifelong appreciation for natural beauty.

He died of natural causes on February 6, 2001, in Minneapolis, Minnesota.