The most difficult Cosmos riddles

The Almagest is a 2nd-century Greek-language mathematical and astronomical treatise on the apparent motions of the stars and planetary paths, written by Claudius Ptolemy (c. AD 100 – c. 170). One of the most influential scientific texts of all time, its geocentric model was accepted for more than 1200 years from its origin in Hellenistic Alexandria, in the medieval Byzantine and Islamic worlds, and in Western Europe through the Middle Ages and early Renaissance until Copernicus.

Warm Breeze is a component of interstellar gas flowing into the interior of the Solar System. In 2014, scientists from the USA, Switzerland and Poland, analyzing data obtained by IBEX, discovered a previously unknown stream of atoms, which is filled with rare and partially ionized matter at a temperature of about 7500 K.

The Kardashev scale is a method of measuring a civilization's level of technological advancement based on the amount of energy a civilization is able to use. It was proposed by Soviet astronomer Nikolai Kardashev in 1964. The scale has three designated categories: a planetary civilization, a stellar civilization and a galactic civilization.

Fallen Astronaut is an 8.5-centimeter (3.3 in) aluminium sculpture created by Paul Van Hoeydonck, meant to intended to commemorate the astronauts and cosmonauts who have died in the advancement of space exploration. During the Apollo 15 mission, near the completion of his work on the lunar surface on August 1, 1971, Scott secretly placed the Fallen Astronaut on the Moon.