Definition of geography | what is astronomy |rare gas | nebula | fusion reaction

Описание: This video provides an introduction to Astronomy (0:05), which is a branch of Geography (0:07) that studies the Universe (0:10). The study of the universe is called Cosmology (0:17). The term "Geography" originates from Greek words "geo" (Earth) and "graphy" (description), meaning "description of the Earth" (0:27-0:46).

The Universe is defined as all visible celestial bodies (1:03-1:21). A Star (1:28) is a celestial body that possesses its own heat and light (1:30-1:41). Before a star forms, it exists as a sphere of Rare Gas (1:56-2:03), such as helium or neon, which has low density and loosely bound atoms (2:11-2:22). As this rare gas forms a dense cloud, it is called a Nebula (2:29-2:43).

Stars are formed through a Fusion Reaction (2:47), specifically the fusion of hydrogen into helium (2:53-2:58). The fuel within a star exists in a Plasma state (3:03-3:18), which is a very hot state of matter. The color of a star depends on its surface temperature (3:20).
Blue or White stars have a high surface temperature (around 4000°C) (3:32-3:40).
Orange stars have a medium temperature (3:43-3:46).
Red stars have a lower temperature (around 6000°C), like our Sun (3:48-3:59).