phys0001_chapter01

phys0001_chapter01 - Chapter 1 Units in Astronomy We...

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Chapter 1 Units in Astronomy We introduce the basic measuring units used by astronomers. Length, measured in meter (m), and time, measured in year (yr) or second (s), are familiar to us. The angular size, measured in degrees (°) or arc seconds, which is very important in astronomy, is not commonly used in everyday life. Length Scales Size does matter. The sizes of various astronomical objects are usually so big that we don't have any feeling about them. Here we list the length scales of some typical objects. You can see that, for example, the ratio of the size of our Sun to the size of the Earth is about the ratio of the size of a human to the size of a bee. Length (m) Object > 10 26 Size of the universe 10 26 Distance to quasars 10 24 Size of a typical cluster of galaxies 10 21 Galaxies 10 18 Globular clusters 10 16 Nebula (clumps of gas and dust), light year 10 13 The solar system 10 9 The Sun 10 7 The Earth 10 6 Great Wall 10 2 Buildings 10 0 Basic unit of distance, humans 10 -2 Coins, bees, bugs
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phys0001_chapter01 - Chapter 1 Units in Astronomy We...

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