Cosmonautics Day, 1975 - Yuri Gagarin - First Man in Space (Soviet Union, USSR 1975)

Stamp Cosmonautics Day, 1975 - Yuri Gagarin - First Man in Space it reflects the thematic directions:

An astronaut (from the Ancient Greek ἄστρον (astron), meaning 'star', and ναύτης (nautes), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally reserved for professional space travelers, the term is sometimes applied to anyone who travels into space, including scientists, politicians, journalists, and tourists

A monument is a type of structure that was explicitly created to commemorate a person or event, or which has become relevant to a social group as a part of their remembrance of historic times or cultural heritage, due to its artistic, historical, political, technical or architectural importance. Examples of monuments include statues, (war) memorials, historical buildings, archaeological sites, and cultural assets. If there is a public interest in its preservation, a monument can for example be listed as a UNESCO World Heritage Site. The Palgrave Encyclopedia of Cultural Heritage and Conflict gives the next definition of monument:

A rocket (from Italian: rocchetto, lit. 'bobbin/spool') is a vehicle that uses jet propulsion to accelerate without using any surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely from propellant carried within the vehicle; therefore a rocket can fly in the vacuum of space. Rockets work more efficiently in a vacuum and incur a loss of thrust due to the opposing pressure of the atmosphere.