Copyright © by Holt, Rinehart and Winston. All rights reserved. CHAPTER 2 STARS, GALAXIES AND THE UNIVERSE

Copyright © by Holt, Rinehart and Winston. All rights reserved. Table of Contents Section 1 Stars Section 2 The Life Cycle of Stars Section 3 Galaxies Section 4 Formation of the Universe Stars, Galaxies, and the Universe

Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 1 Stars

Copyright © by Holt, Rinehart and Winston. All rights reserved. Bellringer What are stars made of? How do stars differ from one another? Do stars move?

Copyright © by Holt, Rinehart and Winston. All rights reserved. Objectives Describe how color indicates the temperature of a star Explain how a scientist can identify a star’s composition Describe how scientists classify stars. Compare absolute magnitude with apparent magnitude. Identify how astronomers measure distances from Earth to stars. Describe the difference between the apparent motion and the actual motion of stars.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Color of Stars Because a blue flame is hotter than a yellow or red flame, we can conclude that blue stars are hotter than yellow or red stars. The color of a star indicates its temperature

Copyright © by Holt, Rinehart and Winston. All rights reserved. Composition of Stars A star is made of different elements in the form of gases. The gases in the atmosphere of a star absorb different wavelengths of light depending on which elements make up the gases. The light from a star indicates which elements make up that star.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Composition of Stars

Copyright © by Holt, Rinehart and Winston. All rights reserved. The Colors of Light A prism breaks white light into a rainbow of colors called a spectrum. An instrument called a spectrograph is used to break a star’s light into a spectrum. The spectrum of a star will vary depending on which elements are present.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Making an ID Emission lines are lines made when certain wavelengths,of light, or colors, are given off by hot gasses. Each elements produces a unique set of emission lines, which allows them to be used to identify the elements in a star.

Copyright © by Holt, Rinehart and Winston. All rights reserved. What Is the Electromagnetic Spectrum? The electromagnetic spectrum is the complete range of electromagnetic waves placed in order of increasing frequency.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Electromagnetic Waves Electromagnetic waves are all around you–in your home, your neighborhood, and your town.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Electromagnetic Waves Activity Click the Active Art button to open a browser window and access Active Art about electromagnetic waves.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Electromagnetic Spectrum Click the Video button to watch a movie about the electromagnetic spectrum.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Emission Lines of Elements

Copyright © by Holt, Rinehart and Winston. All rights reserved. Star Spectrums Astronomers use line spectrums to identify the chemical elements in a star. Each element produces a characteristic pattern of spectral lines.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Trapping the Light––Cosmic Detective Work A star’s spectrum is made of dark emission lines. A star’s atmosphere absorbs certain colors of light, which causes black lines to appear.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Identifying Elements Using Dark Lines Because a star’s atmosphere absorbs some colors of light, the spectrum of a star is called an absorption spectrum. It can be used to identify some of the elements in a star’s atmosphere.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Continuous Spectrum and Absorption Spectrum

Copyright © by Holt, Rinehart and Winston. All rights reserved. Classifying Stars Differences in Temperature Stars are now classified by how hot they are. Class O stars are blue = hot Classifying Stars

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Differences in Brightness – The original scale went from 1-6 The brightest star, Sirius, has a magnitude of The dimmest star that can be seen with a microscope has a magnitude of 29.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Magnitude of Stars in Big Dipper

Copyright © by Holt, Rinehart and Winston. All rights reserved. How Bright Is That Star? Apparent Magnitude The brightness of a light or star is called apparent magnitude. Absolute Magnitude Absolute magnitude is the actual brightness of a star. Absoute and Apparent Magnitude

Copyright © by Holt, Rinehart and Winston. All rights reserved. Distance to the Stars Because stars are so far away, astronomers use light-years to measure the distances from Earth to the stars. A light year is the distance that light travels in a year. Parallax is the apparent shift in the position of an object when viewed from different locations. Measuring parallax enables scientists to calculate the distance between a star and the Earth.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Parallax Parallax is the apparent change in position of an object when you look at it from different places.

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Finding the Distance to Stars: Parallax Visual Concept

Copyright © by Holt, Rinehart and Winston. All rights reserved. Motions of Stars The Apparent Motion of Stars If you look at the night sky long enough, the stars also appear to move. The Actual Motion of Stars The apparent motion of the sun and stars in our sky is due to Earth’s rotation. But each star is also moving in space. Their actual movements, however, are difficult to see.

Copyright © by Holt, Rinehart and Winston. All rights reserved. Apparent Motion of Stars

Copyright © by Holt, Rinehart and Winston. All rights reserved. Actual Motion of Stars

Copyright © by Holt, Rinehart and Winston. All rights reserved. Absolute and Apparent Motion

Copyright © by Holt, Rinehart and Winston. All rights reserved. Star Graphic organizer