Chapter 12.1: View From Earth (Version 2)


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Grade 8 Integrated Science Chapter 12 Lesson 1 on the view of space from Earth. This lesson gives a short introduction on constellations, relative brightness, luminosity, and the apparent size of a star. *This version (Version 2) contains pictures and diagrams of 3 constellations and a white background for easier viewing.

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Chapter 12.1: View From Earth (Version 2)

  1. 1. Chapter 12 Lesson 1 p414-420 THE VIEW FROM EARTH
  2. 2. Vocabulary  Spectroscope – an instrument that spreads light into different wavelengths  Astronomical Unit – the average distance between Earth and the Sun, about 150 million km  Light-year – the distance light travels in 1 year  Apparent Magnitude – a measure of how bright it an object appears from Earth  Luminosity – the true brightness of an object
  3. 3. Looking at the Night Sky  If you look at the stars for a long time they seem to move.  Why does this happen?  Polaris is a star almost directly above the north pole.  As Earth spins Polaris stays in place as stars near it seem to circle around it.
  4. 4.  Polaris is commonly referred to as the Northern Star, because it and the stars near it never set when viewed from the northern hemisphere.
  5. 5. Naked-Eye Astronomy  Naked-eye astronomy means gazing at the sky using just your eyes; no binoculars or telescopes.  Before telescopes, people used the stars to tell time, seasons, and finding directions.
  6. 6. Constellations  When ancient cultures gazed at the night sky, they saw patterns.  They represented people, animals, and objects  The Greek astronomer Ptolemy identified dozens of star patterns nearly 2000 years ago.  These are called ancient constellations today  Present-day astronomers use many ancient constellations to divide the sky into 88 regions also called constellations
  7. 7. ORION
  8. 8. LEO
  9. 9. SCORPIO
  10. 10. Telescopes  Telescopes are able to collect much more light than the human eye  The electromagnetic spectrum is a continuous range of wavelengths  Visible light is only one part of the spectrum  Longer wavelengths have low energy  Shorter wavelengths have higher energy  Different objects in space can emit different types of wavelengths.  The range of wavelengths a star emits is called its spectrum.
  11. 11. Spectroscopes  Scientists study the spectra of a star using a spectroscope.  A spectroscope spreads light into different wavelengths.  This was scientists can study a stars’ characteristics, compositions, and energies.  Newly formed stars emit mostly radio and infrared waves. While exploding stars emit high energy ultraviolet waves.
  12. 12. Measuring distance  Astronomers use angles created by parallax to measure how far objects are from Earth.  Parallax is the apparent change in an object’s position caused by looking at it from 2 different points.  For example: Look at your pencil with only your left eye. Then, without moving the pencil, look at it with only your right eye.  Astronomers create a parallax by using 2 points in Earth’s orbit around the Sun
  13. 13. Distance Within the Solar System  Distances within the solar system are measured using astronomical units or AU.  An astronomical unit is the average distance between Earth and the Sun, about 150 million km.
  14. 14. Distances Beyond the Solar System  Astronomers measure distances beyond the solar system using light-years.  A light-year is the distance light travels in 1 year.  1 light-year equals about 10 trillion km.  The nearest star to our Sun is 4.2 light-years away. How far is that in km?
  15. 15. Looking Back in Time  Because it takes time for light to travel, you see a star not as it is today, but as it was when light let it.  At 4.2 light-years away, Proxima Centauri appears as it was 4.2 years ago.
  16. 16. Measuring Brightness  Astronomers measure the brightness of stars in two ways:  By how bright they are from Earth  By how bright they actually are
  17. 17. Apparent Magnitude  Scientists measure how bright stars appear from Earth using a scale developed by the ancient Greek astronomer Hipparchus  Hipparchus assigned a number to every star he saw in the night sky based on its brightness.  Today these are called number magnitudes  The apparent magnitude of an object is a measure of how bright it appears from Earth  Hipparchus assigned the number 1 to the brightest star he saw in the night sky
  18. 18. Absolute Magnitude  Stars can appear bright or dim depending on their distances from Earth, but stars also have actual, or absolute, magnitudes  Luminosity is the true brightness of an object  This depends on the star’s temperature and size rather then its distance from Earth  A star’s luminosity, distance, and apparent magnitude are all related. Thus, if a scientist knows two of these factor, he can mathematically determine the third.