1. Distances in Space Science 9

2. Using scientific notation Distances in space are very large We use scientific notation to represent very large and very small numbers The first digit is between 1 and 9 This is called the base Followed by a power of 10 The exponent indicates how far to move the decimal point Ex. 2 000 000 000 people = 2 x 10 9 people

3. How Astronomers Measure Distances Triangulation is how astronomers measure distances to objects in the solar system and beyond A baseline gives us a starting point which is used for comparisons The diameter of Earth is often used by astronomers, which is 1.3 x 10 4 km ▫This value can then be used to calculate the distance to stars

4. Distances to the Stars The distance from our Sun to the next nearest star is 4.1 x 10 13 km Because these numbers get so large, astronomers have come up with another way to measure distance, the light year ▫The distance that light travels in one year is equal to one light year ▫Light travels at a speed of 3 x 10 5 km in 1 second ▫In one year, it travels 9.46 x 10 12 km

5. Some Distances of Objects from Earth The light we see from the star Alpha Centauri took 4.3 years ago The most distant known galaxy from Earth is 15 000 000 000 light years from us Measurements in light years not only tell us how far away something is from us but how much time has passed since the light left that object

6. Practice with Scientific Notation 1.Write the following numbers in scientific notation. a.1 000 000 000m b.246 000 000 000 000 000 km c.0.000 000 8mm d.450 m e.0.000 000 000 000 000 12cm f.333 000 000 000 000 000 000 000 000 km

7. For the remainder of class: Questions 2, 4, 5 on page 445 Questions 1, 3, 4, 6 on page 439