Order of Magnitude
•The nearest power of ten of a number is called its  Order of Magnitude. Examples from Tipler’s table 1-3:
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• Size (m)            Mass (kg)           Time (s)
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•Proton 10E-15   Electron 10E-30  Period of visible                                                                                                                         light 10E-13
•Sun      10E9      Sun 10E30          Age of earth       10E17