Stars Galaxies and the Universe Course 3 3

Stars, Galaxies, and the Universe- Course 3 3 -1 The Scale of the Universe

My Planet Diary pg. 94 Florida Space History Voyager Golden Record Sixteen billion kilometers away flies a gold-plated copper disk with a voice saying “Hello from the children of planet Earth. ” The disk is carried aboard Voyager 1, a spacecraft launched in 1977 that once sent back information about the planets of the outer solar system. The disk is filled with images and sounds of Earth. One day, aliens might find Voyager 1 and learn all about us! Voyager 1 is now sixteen billion kilometers away from the sun! What images and sounds would you put on A recording sent into space? ___________________________________

How Do Astronomers Measure Distances to the Stars? Pg. 94 Astronomers often use parallax to measure the distances to nearby stars. Parallax is the apparent change in position of an object when you look at it from different places. Astronomers note the position of a star, then they note its position six months later. They measure how much the star appears to move against a background of stars much farther away. The less the nearby star appears to move, the farther away it is. Parallax works as a measuring tool for distances up to a few hundred light-years from Earth.

The Scale of the Universe Parallax of Stars The apparent movement of a star when seen from a different position is called parallax. Challenge: Hold a finger about half and 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. Why does your finger seem to move? How is this related to the parallax of stars?

Parallax of Stars pg. 95 Astronomers look at a nearby star when Earth is on one side of the sun. Then they look at the same star again six months later, when Earth is on the opposite side of the sun. Astronomers measure how much the nearby star appears to move against a background of stars that are much farther away. They can then use this measurement to calculate the distance to the nearby star. The less the nearby star appears to move, the farther away it is. Astronomers can use parallax to measure distances up to a few hundred light-years from Earth. The parallax of any star that is farther away is too small to measure accurately.

How Do Astronomers Describe the Scale of the Universe? Pg. 96 Astronomers define the universe as all of space and everything in it. The universe is enormous, almost beyond imagination. Astronomers study objects as close as the moon and as far away as quasars. They study incredibly large objects, such as clusters of galaxies that are millions of light-years across. They also study the behavior of tiny particles, such as atoms within the stars.

Scientific Notation and The Light-Year pg. 96 Scientific Notation Since the numbers astronomers use are often very large or very small, they frequently use scientific notation to describe sizes and distances in the universe. Scientific notation uses powers of ten to write very large or very small numbers in shorter form. Each number is written as the product of a number between 1 and 10 and a power of 10. For example, 1, 200 is written as 1. 2 × 10³. Light-Year Astronomers use a unit called a light-year to measure distances between stars. A light-year is the distance light travels in one year, about 9, 460, 000, 000 meters (9. 46 × 10¹⁵ meters in scientific notation).

The Immensity of Space pg. 96.

The Scale of the Universe pg. 97 Scale of the Universe Scientists often use scientific notation to help describe the vast distances in space. Express the distances to the sun and Alpha Centauri in meters by writing out all the zeroes in the number. Sun: ________________________ Alpha Centauri: ___________________

Assess Your Understanding pg. 97 1 a. What is scientific notation? b. How is scientific notation useful to astronomers? c. The Andromeda galaxy is 2, 200, 000 light-years away. Write that measurement using scientific notation.