Distance in Space L IG H T Y E ARS Last lesson: what did we learn? What astronomical units are How to use astronomical units as measures of distances between the Sun, Earth, and other planets Calculate the relative distances
between the planets using a scale distance Draw a scale drawing to accurately depict the distance between planets What will we learn this lesson? What is a light year? Why do we need it?
How can we calculate it? Light years In our solar system, we tend to describe distance in astronomical units However, it is not a big enough of a unit when talking about
objects outside our solar system Instead, astronomers use the unit light year A light year is a unit of distance, not a unit of time. Light years A light year is the distance that
light can travel in 1 year. Light moves at a velocity of about 300,000 km per second. In 1 year, it can travel approximately 9,500,000,000,000 km (or 9.5 trillion km) The Milky Way Galaxy is about 150,000 light-years across. The Andromeda Galaxy is 2.3 million
light-years away. Calculating distances in light years Remember that light travels at approximately 9,500,000,000,000 km/year To simplify calculations: If a star is 25,000,000,000,000 km from Earth
25, 000,000,000,000 km 9,5 00,000,000,000 km 25 = 2.6 light years 9.5 Star Distance away in kilometres
Proxima Centauri 43,000,000,000,00 0 Sirius
90,000,000,000,00 0 Betelgeus e Vega Polaris 5,000,000,000,000,
000 260,000,000,000,0 00 6,800,000,000,000, 000 Distance away in light years
Gravity W H AT IS IT AN D W H Y IS IT I MP ORTAN T? What is gravity? Gravity has played a big part in making the universe the way it is. Gravity is what makes pieces of matter clump together into planets,
moons, and stars. Gravity is what makes the planets orbit the stars - like Earth orbits our star, the Sun. Gravity is what makes the stars clump together in huge, swirling galaxies. Mass vs Weight Mass is a measure of how much matter something contains
Weight is a measure of how strongly gravity pulls downwards Apparent Weight is a measure of downwards force Force is measured in Newtons, not kilograms or pounds When scales show "kg" or "lb" it is just an estimate of the mass above them
