Characteristics of Stars
The characteristics used to describe stars are size, colour, temperature, luminosity
(brightness) and density.
Scientists have discovered that the temperature of a star can be estimated by its.
Example:
Red
→
relatively cool
Orange
→ warmer Yellow
→
warmer still . . . temp. of our Sun
White
→ even warmer . . . temp. of Sirius
Blue
→ hottest temperature
The brightness of stars can be described in two ways:
1. Apparent magnitude – The brightness of the start as it appears from Earth, therefore it depends on how far the star is from the Earth and how much light it emits. 2. Absolute magnitude – How bright a star would appear if it were seen from the same distance.
Life Cycle
• All stars begin their life as Nebulas which are huge clouds of dust and gases mainly hydrogen and helium
• Over time, the hydrogen gas in the nebula is pulled together by gravity and it begins to spin. • When the hydrogen supply in the core begins to run out, and the star is no longer generating heat by nuclear fusion, the core becomes unstable and contracts.
• As it expands, it cools and glows red. The star has now reached the red giant phase.

Average Star
• Gravity causes the last of the matter in the start to collapse inward and all that is left is a hot dense core of matter called a white dwarf
• White dwarfs shine for billions of years before they completely cool
• When a White Dwarf no longer emits energy it may become a dead star or black dwarf, it is thought that black dwarfs do not exist yet as the universe is not old enough to have produced them.
Massive Star
• A massive star will undergo a supernova explosion.
• In a large star the core material packs together as a neutron star.
• In extremely large stars the core material packs tightly together as a black hole

Galaxies
• Galaxies are large groups of stars bound