1957-07-01 International Geophysical Year

The first International Geophysical Year (1957) stamp from Russia, postmarked on cover, Moscow July 1, 1957, the start of the International Geophysical Year.
The International Geophysical Year was an international scientific project that lasted from July 1, 1957, to December 31, 1958. The IGY encompassed eleven Earth sciences: aurora and airglow, cosmic rays, geomagnetism, gravity, ionospheric physics, longitude and latitude determinations (precision mapping), meteorology, oceanography, seismology, and solar activity.

Rocket mail from the Rocket Research Institute, flown in rocket number 3, postmarked Topaz, July 1, 1957, the start of the International Geophysical Year.
Both the Soviet Union and the U.S. launched artificial satellites for this event; the Soviet Union's Sputnik 1, launched on October 4, 1957, was the world's first successful artificial satellite. Other significant achievements of the IGY included the discovery of the Van Allen radiation belts by Explorer 1 (launched on January 31, 1958) and the defining of mid-ocean submarine ridges, an important confirmation of plate-tectonic theory. Also detected was the rare occurrence of hard solar corpuscular radiation that could be highly dangerous for manned space flight.

(Reference from International Geophysical Year)