DISTANCES IN SPACE - Notes
 The light from the stars we see at night travel great distances to reach Earth.
 Other than the sun, Proxima Centauri is the next closest star.
 The light that we see from it takes over 4 years to reach our eyes.
 Other light from stars has taken thousands, millions, or even billions of years to reach Earth.

Units we use to measure distances on Earth are way too small for the extremely large distances in space.
 The distance between the Earth and the Sun for example is 150,000,000 km or 93,000,000 mi.
 1AU (Astronomical Unit) = 93 million miles = the distance from the Earth to the Sun
 Our closest star, Proxima Centauri is 24.8 trillion miles or 260,000 AU
o Proxima Centauri is 4.2 light years away.
What is a Light Year?

A unit that measures the distance light travels in one year

Light travels 9.5 trillion km in one year (5.8 trillion miles)
Light travels 300,000 kilometers every second
 Sunlight reaches Earth in 8 minutes
 Sunlight reaches Pluto: 4 hours

Light from Proxima Centauri reaches Earth: 4.2 years
How do astronomers measure the distance to stars?
 One method astronomers use to measure distances to stars is called parallax.
 Stars that are close to Earth show parallax as Earth moves from one side of the sun to the other.
 Astronomers can then determine the distance using geometry!