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The Speed of Light.

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Presentation on theme: "The Speed of Light."— Presentation transcript:

1 The Speed of Light

2 How fast does light travel?
The transmission of light is not instantaneous! Light takes time to travel from a light bulb to your eye. Despite light being the fastest thing known, the speed of light can still be measured! The speed that light travels is 300,000 km/sec or 186,000 miles/sec!

3 What is a light year??? The distance light travels in one year is called a light year! This is an astronomical unit astronomers use to express how far away an object is!

4 So…how far does light travel in a year????
300,000 km/sec x 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr = 9,460,800,000,000 km or 9.5 trillion kilometers 186,000 mi/sec x 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr= 5,865,696,000,000 mi or 6 trillion miles

5 Can we see back in time? Yes!
Remember light travel is not instantaneous, therefore when a photon of light leaves a star it takes time to travel to your eye. The time it takes depends on its distance from Earth. It takes less time for you to travel to Sacramento than to LA, therefore a star that is farther away will cause the photon of light to take a longer time to reach your eye.

6 Looking back into time How far away an object is determines how long ago we are seeing back in time. Example: The North Star (Polaris) is 360 light years away. Take the year that it is now and subtract the distance from the year l.y. = the year 1650 A.D. If your answer is a negative number, then it occurred in B.C. In other words you are seeing Polaris as it was back in the year 1650 A.D.

7 Looking into the Future!
So when will you see the photon of light that is leaving the star at this very moment? Example: Polaris is 360 l.y. away. Take the year that is us now and add the distance to the year. l.y. = 2370 A.D. So in the year 2370, you will finally see the photon of light that left Polaris today! Wow! Challenge: What is the distance in miles to Polaris? Kilometers?

8 Answer to the Challenge
Miles: 360 l.y. x 6 trillion miles = 2.16 x 1015 Kilometers: 360 l.y. x 9.5 trillion km = 3.4 x 1015

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