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One light year is equal to the distance traveled by light in one year (through empty space). One light year = 1 ly = 6 trillion miles = 9.5 trillion kilometers Wait a minute! How do we know how far one light year is? QUESTION: How far will you travel in 3 hours if your speed is 50 miles per hour? ANS: ___________________ The secret to this calculation is ___________ = _____________ x _____________ Calculating a light year Using the formula d = vt, with v = c = 3.00 x 105 km/s t = one year = 3.15 x 107 s 1 ly = 3.0 x 105 x 3.15 x 107 or 1 ly = 9.45 x 10 12 km Some interesting distances: To star nearest the sun….4 ly To edge of our galaxy.…. 50,000 ly To nearest galaxy .......…. 2,000,000 ly