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This chapter delves into the fascinating world of stars, galaxies, and the universe. It covers the life cycle of stars, the formation of galaxies, and the overall creation of the universe. Learn about the composition of stars, how scientists classify them, and the different colors of light they emit. Discover how astronomers measure distance in light-years and the apparent and actual motion of stars.
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CHAPTER 2 STARS, GALAXIES AND THE UNIVERSE
Stars, Galaxies, and the Universe Table of Contents Section 1 Stars Section 2 The Life Cycle of Stars Section 3 Galaxies Section 4 Formation of the Universe
Bellringer • What are stars made of? • How do stars differ from one another? • Do stars move?
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. • Identifyhow astronomers measure distances from Earth to stars. • Describe the difference between the apparent motion and the actual motion of stars.
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
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.
The Colors of LightA 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.
Making an IDEmission 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.
The electromagnetic spectrum is the complete range of electromagnetic waves placed in order of increasing frequency. What Is the Electromagnetic Spectrum?
Electromagnetic waves are all around you–in your home, your neighborhood, and your town. Electromagnetic Waves
Click the Active Art button to open a browser window and access Active Art about electromagnetic waves. Electromagnetic Waves Activity
Click the Video button to watch a movie aboutthe electromagnetic spectrum. Electromagnetic Spectrum
Astronomers use line spectrums to identify the chemical elements in a star. Each element produces a characteristic pattern of spectral lines. Star Spectrums
Trapping the Light––Cosmic Detective WorkA star’s spectrum is made of dark emission lines. • A star’s atmosphere absorbs certain colors of light, which causes black lines to appear.
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.
Classifying Stars • Differences in TemperatureStars are now classified by how hot they are. • Class O stars are blue = hot • Classifying Stars
Differences in Brightness – The original scale went from 1-6 The brightest star, Sirius, has a magnitude of -1.4. The dimmest star that can be seen with a microscope has a magnitude of 29.
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
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.
Parallax is the apparent change in position of an object when you look at it from different places. Parallax
Finding the Distance to Stars: Parallax Visual Concept Visual Concept
Motions of Stars • The Apparent Motion of StarsIf you look at the night sky long enough, the stars also appear to move. • The Actual Motion of StarsThe 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.
