SPEED OF LIGHT

Lesson 5:  Why We See Back In Time

Space and Time are intertwined 

Key Principles:

1. Speed of Light 

   1. 1.86 x 10 to the 5th miles/second (Standard form 186000 mi/s)

   2. We figured out how far light travels in a year. (Light Year)

   3. 1 Light Year is the metric we use to describe stellar distances. 

   4. Example:  POLARIS is 323 Light Years Away

      1. So the light that we will see from POLARIS, was produced 323 YEARS AGO!!!!  You are seeing an image of POLARIS back in time!

2. The Universe is Expanding

   1. We’ve noticed that the universe is moving away from us at all angles.  (Means it must be expanding)

   2. Doppler Effect - both sound and light wave frequencies either expand or contract, based on the movement of the object generating those wave frequencies.  However, the speed of sound and the speed of light are constants. (The speeds don't change, only their internal properties change) 

      1. When something moves away, it’s wavelengths stretch.  Stars emit light that bends to a red color on the spectrum when they’re moving away from us.

      2. When something moves closer, it’s wavelengths compress.  Stars emit light that squeezes to a blue color on the spectrum when they’re moving toward us.  

      3. WE WILL REVISIT THIS IN THE FUTURE….OR WILL IT BE THE PAST?  Depends on where you are in the universe...