For the Greeks this term was commonly employed with two distinct meanings: on the one hand it designates the occasion which does not wait, the critical hour where all reversals are possible; on the other hand its represents a happy medium, its meaning thus approaching the idea of propriety and equilibrium.

Chalky ground affected by the action of dissolution by waters and leading to the formation of caves, rock failures and abysses.

Katanga is the southern most province in the Democratic Republic of Congo (RDC). Its capital is Lubumbashi, previously called Elisabethville. It is a province which is both agricultural (on the plateau) and industrial as, in the East and the South, it harbours very rich deposits of various metals: copper, cobalt, iron, uranium, etc. It came under Belgian control in 1908, which began to exploit its mineral resources and their established workers from the North of the province and from Kasaï, a neighbouring province, or from neighbouring countries. When the Congo achieved independence in 1960, Katanga seceded. More than two years of civil war were necessary to bring Katanga back into the Congo’s family fold (1963). In 1966 the Congolese government nationalized the Upper Katanga Mining Union (the country’s largest mining company), under the name of Gécamines. In 1971, at the time of the Zairisation of the country, Katanga became Shaba. Several periods of unrest and attempts rebellions took place in the 1970s. Thus in 1978 Angolan rebels invaded Kolwezi and detained close to 3000 European nationals. The latter were liberated thanks notably to the actions of the Belgium and French armies (attack by the Foreign Legion on Kolwezi). The province once again took the name of Katanga in 1997.

An American actor, singer, dancer and director. He remains known above all for his talent for choreography, which burst through in his three most famous films: A Day in New York (1949), An American in Paris (1951) and Singing in the Rain.

A kelvin (K) is a unit of temperature, just like a degree on the Celsius (°C) scale (which people on the continent use). A temperature of zero Kelvin equals –273.15 °C, which is absolute zero, the coldest temperature possible in the universe.

Cells which make up 90% of the epidermis and the keratinous appendages (nails, hair, fur, feathers, scales). They synthesise keratine, a protein which is insoluble in water, which provides the skin with its impermeability.

The kinetoscope, conceived by the American inventor Thomas Edison in 1888, was one of the first cinematographic viewing appliances. It is a kind of box, one and a half metres high, in which, via a peephole, a single viewer can see unfold on a loop the images of a negative film 17m long, at 48 images per second. Its low brightness did not allow for public projection, but it was on the basis of similar techniques that the Lumière brothers constructed the first cinema ‘projectors’ such as we understand them today.

A knock-out animal (usually a mouse) has had introduced into its body a specific modification in the coding structure of a gene and in its regulating components, in order to inhibit or modify the functioning of the gene in the animal under study. This allows researchers to observe the consequences of, e.g., the suppression of a gene, and to study the effects of a gene on an organism by its absence, or the absence of its functioning.

Sergey Korolyev was born in 1907 in Jitomir, in Ukraine. An engineer in aeronautics, he was arrested in 1938 during a Stalinist purge, tortured and sent to the gulag. In 1940, whilst remaining a prisoner, he became a member of a team of engineers charged with military aeronautical research. He was freed in 1944 and then given the responsibility of penetrating the secrets of the German V2 missile, developed by Werner von Braun. He then imposed himself as chief designer of the Soviet space programme, even though his name was never cited for political reasons. He developed Semiorka, a rocket which is still active today and which launched the first Sputnik. It is also thanks to him that the USSR was able to send the first man into space. He died on January 14th, 1966, in Moscow.

A secrete North-American society created after the American Civil War in 1867. Characterized by violent xenophobia, the Klan fights against the integration of black people.

The Kuiper belt is a ring with a vast population of small frozen objects (comets, asteroids, ...). In the Solar System plane, the Kuiper belt extends just beyond the orbits of Neptune and Pluto, the farthest planets. The Kuiper belt takes its name from the astronomer Gerard Kuiper who predicted its existence in 1951 based on theoretical developments. We would have to wait until the 1990s to have the first observational evidence of its existence.