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1 Stars on the Move • Every single object in the universe is on the move. • A spectroscope enables scientists to determine whether a particular galaxy is moving toward the earth or away from the earth. 2 The Red Shift • Light travels from stars as light waves. • A spectroscope breaks up light into a spectrum because each color of light has a different wavelength. • If a star is rapidly approaching the earth, the light waves from the star will appear compressed, or pushed together. 3 • Wavelengths from an approaching star often appear shorter than they really are. • Shorter wavelengths of light are characteristic of blue and violet light. 4 • The entire spectrum of an approaching star appears to be shifted toward the blue end of the spectrum. • This shifting is called the blue shift. 5 • If a star is moving away from the earth, the light waves will be slightly expanded. • The wavelengths of the light will appear longer than they really are. • Longer wavelengths of light are characteristic of the red end of the spectrum. 6 • The spectrum of a star moving away from the earth appears to be shifted toward the red end. • This is called the red shift. • The more the spectrum of light is shifted toward the blue or red end of the spectrum, the faster the star is moving toward or away from the earth. 7 8 • The apparent change in the wavelengths of light that occurs when an object is moving toward or away from the earth is called the Doppler effect • Sound 9 • When astronomers first used the spectroscope to study the light from stars in distant galaxies, they discovered that none of the light from these distant galaxies showed a blue shift. • None of them were moving toward the earth. 10 • Light from every distant galaxy showed a red shift. • Every galaxy in the universe seemed to be moving away from the earth. • Based on the examinations of these red shifts, astronomers concluded that the universe is expanding. 11 • Galaxies near the edge of the universe are racing away from the center of the universe at tremendous speeds. • Galaxies closer to the center are also moving outward, but at slower speeds. 12 The Big Bang Theory • Astronomers believe the expanding universe is the result of an enormous and powerful explosion called the big bang. • The big bang theory may explain how the universe formed. 13 14 • The big bang theory states that the universe began to expand with the explosion of concentrated matter and energy and has been expanding ever since. 15 • According to the theory, all of the matter and energy in the universe was then concentrated into a single place. • The big bang shot the concentrated matter and energy in all directions. 16 •The fastest moving matter traveled farthest away. •Energy also began moving away from the area of the big bang. 17 • If the big bang theory is correct, the energy left from the big bang will be evenly spread out throughout the universe. • This energy is known as background radiation. 18 • Scientists have discovered that the background radiation in the entire universe is the almost the same everywhere. • This constant background radiation is one observation that supports the big bang theory. 19 • After the initial big bang, the force of gravity began to affect the matter racing outward in every direction. • Gravity is a force of attraction between objects. • All objects have a gravitational attraction for other objects. 20 • The more massive the object is, the stronger its gravitational attraction is. • This force of gravity began to pull matter into clumps. • The clumps formed huge clusters of matter. • These clumps became the galaxies of the universe. 21