11 April

2001: On 11 April 2001, ESA signed a treaty with the French government concerning the future of the Guiana Space Centre (CSG), Europe's Spaceport in French Guiana.

The agreement extended the French government's guarantee of ESA's access to facilities and resources belonging to the Centre National d'Etudes Spatiales at the CSG and use of them for its programmes and activities, in particular Ariane launcher operations.

1986: On 11 April 1986, Comet Halley made its closest approach to Earth on its current orbit, 63 million kilometres, on its outbound journey. Many observers were disappointed because the famous comet was barely visible to the naked eye. Some years are simply better than others - such as in 1066 when the comet was so bright that it terrified millions of Europeans.

Comet Halley will visit Earth again until 2061 when it returns on its 76-year orbit. This comet's closest known approach to the Earth was 3 million miles on 10 April 837 AD.

On 13 March 1986, ESA's Giotto mission flew past Comet Halley.

1970: On 11 April 1970, NASA launched Apollo 13. NASA intended Apollo 13 to be the third mission to land on the Moon. An explosion in one of the oxygen tanks crippled the spacecraft during flight and with the famous understatement reporting the event, "Houston, we've had a problem," the crew were forced to orbit the Moon and return to the Earth without landing.

1798 On 11 April 1798, Macedonio Melloni was born. He was an Italian physicist who was the first to extensively research infrared radiation. After Herschel's discovery of infrared radiation a generation before, suitable tools were not available until the invention of the thermopile in 1830. That instrument was a series of strips of two different metals that produced electric current when one end was heated. Melloni improved the thermopile and used it to detect infrared radiation. In 1846, from an observation point high on Mount Vesuvius, he measured the slight heating effect of moonlight. He showed also that rock salt, being transparent to infrared, made suitable lenses and prisms to demonstrate the reflection, refraction, polarisation and interference of infrared in the same manner as visible light.

Observing in the infrared is now extremely important to astronomers. ESA first studied the infrared with its ISO mission and is currently working on another mission, Herschel.