Karl Guthe Jansky

Karl Guthe Jansky was an American physicist and radio engineer. He is known as a founding figure of radio astronomy. This is the study of celestial objects using radio waves instead of visible light. In April 1933, Jansky announced he had found radio waves coming from the Milky Way. His discovery changed how humans observe the universe.

Jansky grew up in a family with deep scientific roots. He was born in 1905 in the Oklahoma Territory. His father, Cyril M. Jansky, was the dean of engineering at the University of Oklahoma. Karl attended the University of Wisconsin for his studies. He earned a Bachelor of Science in physics in 1927. He later completed graduate coursework for a master's degree in physics. In 1928, he joined the Bell Telephone Laboratories in New Jersey. He moved to Holmdel because of a kidney condition.

At Bell Labs, Jansky was assigned to investigate sources of static. This static could interfere with trans-Atlantic radio telephone services. He built a large, directional antenna to study these signals. The antenna was about 100 feet in diameter and 20 feet tall. It operated at a frequency of 20.5 MHz. The device sat on a turntable with Ford Model-T wheels. This allowed the antenna to rotate in the azimuthal direction. People called it "Jansky's merry-go-round."

Jansky used an analog pen-and-paper system to record signal intensity. He categorized the static into three distinct types. The first type came from nearby thunderstorms. The second type came from distant thunderstorms. The third type was a faint, mysterious "hiss" of unknown origin. Jansky spent over a year investigating this third signal. He noticed the intensity rose and fell once every day. At first, he thought the radiation came from the Sun.

Jansky eventually realized the signal was not from the Sun. He found the signal repeated on a cycle of 23 hours and 56 minutes. His friend, Albert Melvin Skellett, identified this as a sidereal day. A sidereal day is the time it takes fixed stars to pass overhead. This proved the signal came from astronomical objects. By comparing his data to maps, Jansky located the source. The radiation was strongest in the direction of the Milky Way. Specifically, it came from the constellation Sagittarius.

Jansky announced his findings in April 1933. He published a paper titled "Electrical disturbances apparently of extraterrestrial origin" later that year. He even discussed "Radio sounds from among the stars" on NBC. In 1935, he suggested the signals came from interstellar gas. He believed this was caused by the thermal agitation of charged particles. Despite this, radio astronomy remained a quiet field for a while. The Great Depression made it difficult for observatories to fund new research.

Other scientists eventually built upon his work. Grote Reber built a radio telescope in his backyard in 1937. He performed the first systematic survey of radio waves. John D. Kraus later started a radio observatory at Ohio State University. Jansky's legacy is preserved in many ways today. Scientists use the "jansky" (Jy) as a unit for spectral irradiance. There is a crater on the Moon named Jansky. The Karl G. Jansky Very Large Array is a major telescope in New Mexico.

Jansky died in 1950 at the age of 44. He passed away due to a heart condition. Today, his work is honored by the National Radio Astronomy Observatory. They award the Jansky Prize every year. A monument in Holmdel, New Jersey, marks the site of his original antenna. The sculpture is pointed toward the center of our galaxy. It honors the moment he discovered the sounds of the stars.