## Speed Of Light

All kinds of electromagnetic waves move through empty space at the same speedâ€”that is, at the speed of light. The speed of light in empty space, usually symbolized by the letter c, is practically 300,000 km/second (186,000 miles per second).

The speed of light in empty space has been called the "speed limit of the universe," because no known object can be accelerated to move faster. It is one of the most important and precisely measured numbers in astronomy (Appendix 2).

A light-year (ly) is the distance light travels through empty space in one year.

How many kilometers (miles) does 1 light-year represent? Tips: (1) distance = speed x time. (2) A year is equal to 3.156 x 107 seconds._

Answer: Practically 9.5 trillion km (6 trillion miles).

Solution: Multiply 300,000 km/second x 3.156 x 107 second/year (186,000 miles/second x 3.156 x 107 seconds/year)

## Telescopes Mastery

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