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-          What is light?-           

-          Light is an electromagnetic wave that also comes in "photons"

-          Each type of light or photon has a different wavelength, frequency and energy.

-          In order of increasing wavelength, the forms of light are gamma rays, x-rays, ultra-violet, visible light, infrared, micro waves, radio waves

           What is matter?   

-          Ordinary matter is made is of atoms.

-          Atoms are made of protons, neutrons, and electrons.

-          Isotopes  of a particular chemical elements have the same number of protons but different numbers of neutrons 

-          Matter can emit (lamp) , absorb, transmit (mirror, glass) or reflect light

-          How does light tell us the temperatures of planets and stars?

  Objects such as planets and stars produce thermal radiation spectra, the most common type of continuous spectra. We can determine the temperatures from these objects because the hotter the objects are the more radiation per unit area and emit photons with a higher energy.

How does light tell us the speed of a distant object?

The Doppler Effect tells us how fast an object is coming towards or us or away from us. Spectral lines are shifted to shorter wavelengths for objects moving towards us and longer wavelengths for objects moving away from us.