Earth and Space Science / Unit 10: Stars, Galaxies and the Universe
10.1 Properties of Stars
Notes
Stars are balls of plasma powered by fusion. We learn about them from their light.
- Distance is measured in light-years (ly): the distance light travels in one year, about 9.5 trillion km. The nearest star after the Sun, Proxima Centauri, is 4.2 ly away.
- Parallax: nearby stars appear to shift against distant stars as Earth orbits the Sun; bigger shift means closer.
- Color shows temperature: blue stars are hottest (above 10,000 K), red are coolest (about 3,000 K), yellow like the Sun (5,800 K).
- Luminosity is the total energy output; apparent brightness depends on distance too.
- A star's spectrum shows its composition.
- Example: light from a star 20 ly away left it 20 years ago.
Practice
A light-year is a unit of:
It is the distance light travels in a year.
Which star color is the hottest?
Blue stars have the highest surface temperatures.
We see light from a star 50 ly away. That light left the star:
One light-year of distance equals one year of travel.
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