1. The scale of the universe How do astronomers measure distances to the stars? How do astronomers describe the scale of the universe?

2. Parallax of stars: the change in position of an object when looked at from different places. Using parallax to find distance is not a direct measurement. It provides information astronomers use to calculate distance. Hold a finger about half an arm’s length away from your face. Switch back and forth between closing your left and right eye and watch how your finger appears to move against the background. The position of your finger seems to move exactly the same way as the position of the star appears to move when viewed from different places in earth’s orbit.

3. Astronomers define the universe as all of space and everything in it. Distances in astronomy are often very large. Instead of writing out the number with many zeros scientists use scientific notation. Astronomers use a unit called the light - year to measure distances between the stars. In space light travels at the speed of about 300,000,000 meters per second. A light year is the distance that light travels in one year about 9.46 trillion kilometers

4. Key concepts review: What is a light - year based on? It is the distance light travels in one year. How many kilometers are equal to a light - year?9.46 trillion kilometers. How would you write this in scientific notation? 9.46 x 10 to the 12 th power.

5. Scale of the universe summary Astronomers often use parallax to measure the distances to nearby stars. Parallax is a change in position of an object when you look at it from different places. Astronomers note the position of the star then they note its position six months later. They measure how much the star appears to move against the background of stars much farther away. The less the nearby stars appear to move the farther away it is. (question in Winter’s interim test)