65 years ago today, June 25, 1960 (June 2, 1960 in the lunar calendar), French astronomer Walter Bard passed away. Wilhelm Heinrich Walter Baade?, March 24, 1893-June 25, 1960) was a German astronomer who spent most of his scientific career in the United States. Bard proposed the concept of two types of star populations, correctly distinguished two types of Cepheid variable stars, and made important revisions to the scale of cosmic distance. Life Bader was born in Schlettinghausen, Germany in 1893. During his youth, he studied at the universities of Munster and Göttingen. Received his doctorate in 1919. He then worked at the Bergdorf Observatory at the University of Hamburg. Bard immigrated to the United States in 1931 and worked at the Mount Wilson Observatory. In 1948, he joined the Paloma Observatory and retired in 1958. After retirement, Bard returned to Göttingen and died in 1960. While working at the Mount Wilson Observatory, Bard collaborated with American astronomers Fritz Zwicky and Edwin Hubble to study supernovae and galaxies. The Mount Wilson Observatory had the largest 100-inch (2.5-meter) telescope in the world at the time. In 1934, he and Zwicky published an article in the Proceedings of the National Academy of Sciences, proposing that the term "supernova" be used to describe the transformation process of normal stars into neutron stars and to explain the origin of cosmic rays, which was a very surprising view at the time. In 1935, under the joint initiative and promotion of him and Zweiki, the first Schmidt telescope was built at Paloma Observatory with a diameter of 45/65 centimeters. In 1934, he and Zweiki jointly published an article stating that neutron degenerate pressure could support stars with masses exceeding the Chandrasekhar limit. During World War II, many astronomers were recruited into the military. Bader stayed at the Mount Wilson Observatory as a German expatriate, which allowed him to use the telescope freely, and few people competed with him for the time of the telescope. And the nearby city of Los Angeles implemented wartime blackouts, which greatly reduced light pollution and created good conditions for Bard to conduct astronomical observations. Bard used a 2.5-meter telescope to break down a single star in the Andromeda Galaxy for the first time. He also proposed the concept of star population: one type is young stars, mainly distributed in the spiral arms of galaxies, called population I. The other type is elderly stars, distributed in the central and halos of the galaxy in globular clusters, called population II. After the end of World War II, Bard entered the Paloma Observatory and continued his research using the Paloma Observatory's new 200-inch (5-meter) telescope. He found that each of the two star populations has its own unique family of Cepheid variable stars. Population I Cepheid variable stars and population II Cepheid variable stars have different circumferences and light relationships. Hubble attempted to determine the distance of the Andromeda Galaxy for the first time. He mistakenly applied the circumfluence relationship of population II Cepheid variables to population I Cepheid variables of the Andromeda Galaxy, and the result was 800,000 light-years. Bard used the correct circumspect relationship to recalculate the distance of the Andromeda Galaxy and got a result of 2 million light-years. This means that almost all galaxies that use redshifts to measure distances are more than twice as distant as previous estimates, which also increased people's estimate of the age of the universe from 2 billion years to 5 billion years at that time, solving the problem that the earth is older than the universe. Contribution Bard also discovered 10 asteroids. In memory of the astronomer, Asteroid 1501, a crater on the moon, a lunar valley, and one of the Magellan Telescope were all named after him,"Budd."