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Post-program activity copypage Reading – “The Night Sky” Read this passage about the night sky and answer the questions on the back of the page. THE NIGHT SKY If you go outside on a clear night and look at the sky, what do you see? Stars of course. Thousands of them. In fact on a dark night, you may be able to see about three thousand stars without the aid of binoculars or a telescope. WHAT IS A STAR? Stars are glowing, rotating balls of gas. Even though you may see thousands of stars, you are only seeing a small fraction of the stars in our universe. Scientists estimate that there are more than a thousand billion billion stars in our universe! However, almost all of them are too far away for you to see with your naked eyes. From our perspective on earth, stars appear as tiny points of light, but of course, they are much, much larger than they seem. A medium-sized star like our sun could hold more than a million earths inside it! Other stars such as supergiants may be thousands of times larger than our sun. But the enormous distance between them and our earth makes tham appear tiny in the night sky. So what makes a star shine? Hot gases under enormous pressure undergo a process called nuclear fusion that causes the star to give off energy in the forms of light and heat. Some stars may reach temperatures of millions of degrees! STAR COLORS You can tell the temperature of a star just by noticing its color. Stars with the coolest surface temperatures are the red. Their temperatures reach about 3,000 degrees Kelvin. Examples of these are the stars Betelgeuse in the constellation Orion and Antares in the constellation Scorpio. Yellow stars, such as our sun, are in the middle of the temperature scale. Our sun reaches 6,000 degrees Kelvin on its surface. Finally, the blue colored stars are the hottest of them all. Blue stars such as Rigel in the constellation Orion, and Spica in the constellation Virgo have surface temperatures of up to 25,000 degrees Kelvin. CONSTELLATIONS For thousands of years, humans have looked at the night sky and played “connect the dots.” By connecting stars that appear to be close together, the eighty-eight different constellations of the night sky have been created. Some famous constellations include Hercules, the brave son of Zeus, Cassiopeia, the beautiful queen of Ethiopia, Orion, the brave hunter, and Hydra, the nine-headed serpent. The legends surrounding these mythological characters are still known to us today. “The Night Sky” Questions Directions: Use the story “The Night Sky” to answer these questions. 1. Why can’t you see all the stars in the universe when you look up at the night sky? A. The sky isn’t dark enough. B. The earth is too big. C. You could if you could just stay up late enough. D. Most stars are too far away to be seen with your eyes. 2. What is the process called by which stars create light and heat? A. combustion B. nuclear fusion C. burning D. evaporation 3. What is the scale used to determine the temperature of a star? A. Celsius B. Kelvin C. Fahrenheit D. heat index 4. Which is the hottest of the stars? A. a red supergiant B. a medium-sized yellow star C. a blue star D. They are all the same temperature. 5. How many constellations are there in the night sky? A. 25 B. 68 C. 88 D. 104 Some information taken from Ranger Rick’s NatureScope “Astronomy Adventures”, McGraw-Hill Publishers, copyright 1989.