2003: On 1 April 2003, ESA's Maxus 5 sounding rocket mission was successfully launched from Esrange, north of the Arctic Circle near Kiruna in northern Sweden.
The rocket carried a payload of five scientific experiments. They were designed to investigate phenomena in biology, fluid physics, material science and fundamental physics.
Maxus 5 hurtled upwards through a partially cloudy sky to reach a maximum speed of about 3600 metres per second and maximum height of just over 700 kilometres. From booster burn-out 70 kilometres up, until atmospheric re-entry 740 seconds later, the payload experienced excellent microgravity conditions. The payload package was found soon after landing and was recovered by two helicopters.
1960: On 1 April 1960, TIROS-1 went into orbit. It was the first weather satellite and returned 22 952 cloud cover photos. TIROS spacecraft were the beginning of a long series of American polar-orbiting meteorological satellites.
TIROS was followed by the TOS (TIROS Operational System) series, and then the ITOS (Improved TIROS) series, and later the NOAA series. The objective was to establish a global weather satellite system.
1948: On 1 April 1948, Alpher, Bethe and Gamow's famous letter to Physical Review was published. The 'Big Bang' theory had previously been around as a competing theory with 'Steady State' for a while. Their paper gave a 'hot Big Bang' mathematical analysis of atomic events during the creation of the universe, and explained the relative abundances of the light elements (particularly helium) in the Universe.
In fact, the paper was written by Alpher and Gamow. The esteemed Hans Bethe was persuaded to lend his name as a co-author for the amusing similarity to alpha, beta, gamma, the first letters of the Greek alphabet. Bethe did actually make later contributions to disccussions of the theory.