Stars and galaxies in the universe

A galaxy is a set of millions of stars with gas and dust particles. A cloud of dust and gas is a nebula; the Sun and its planets form the solar system.

The Milky Way is a medium-large spiral galaxy. Andromeda is also a spiral galaxy.

The solar system lies at the edge of one of the spiral arms of the Milky Way galaxy.

Stars are formed from nebulae, which are large clouds of dust and gases such as hydrogen and helium.

When the temperature and pressure in the core are very high, hydrogen turns into helium in a nuclear reaction, which releases heat and light.

3 500 K to 5 000 K is the orange range. Red is below 3 500 K and yellow is 5 000 K to 6 000 K.

Light and any matter that enters a black hole cannot escape, so it appears black. A black hole does have gravitational force.

The Sun is a medium-sized star. It becomes a red giant and then a white dwarf. Neutron stars and black holes come from large and super-large stars.

A super-large star that explodes as a supernova becomes a black hole. A large star would become a neutron star and a medium-sized star a white dwarf.

Bluish-white stars are 11 000 K to 25 000 K, so R (14 000 K). S is above 25 000 K (blue), Q is yellow and P is red.

Brightness depends on size, distance and surface temperature. With size and temperature equal, the nearer star looks brighter.

Only super-large stars become black holes. The Sun is a medium-sized star, so it becomes a red giant and then a white dwarf, without a supernova. The Sun is a star, not a planet.