a closer look at light…

A closer look at light…

• Light is a form of electromagnetic radiation that travels in waves.

• Most forms of EM radiation are invisible.• Light waves do not need a medium like water or

air to travel through. Empty space is fine.

WHAT IS LIGHT?

Electromagnetic Radiation• Every object in the

universe emits some kind of radiation.

• The wavelength of light determines the characteristics of each form of radiation.

1. If you listen to music on the radio = radio wave radiation.

2. If you use a microwave = microwave radiation

3. Military & police may use infrared goggles to see body heat in the dark = infrared radiation

4. Visible light lets us see color.

5. An example of Ultra-violet radiation is a sunburn.

6. If you have an x-ray taken = x-ray radiation.

7. Radioactive materials emit Gamma ray radiation.

Visible Light and the Prism• Visible white light is made

up of various colors as seen in a rainbow.

• When sunlight passes through a prism, the waves are refracted (bent) and a rainbow called a spectrum is produced.

SPECTROSCOPE• A tool astronomers use to separate starlight

into a spectrum.• A prism is inserted into a telescope to split

the light into its colors.

The spectroscope can tell astronomers...

• What a star is composed of• How hot a star is• How fast a star or galaxy is moving • The direction a star or galaxy is moving

Types of Spectrums

Continuous• An unbroken band of colors• The source emits light of all visible

wavelengths

Emission • Unevenly spaced lines of different colors.• The source emits light of certain wavelengths. (l) • Every element has a unique emission spectrum.

Absorption• A continuous spectrum crossed by dark lines.

• Determines elements in cool gases.

Each element has a unique spectrum.

• By observing the spectra of distant stars we learned what elements make up the atmosphere of stars (and planets).

Argon 

                                                 Helium

Mercury

                                                 Sodium

 Neon

The Doppler Effect

Sound• Think about the sound a train makes as it approaches you

compared to when it moves away from you.

• There is a change in the pitch of the sound.• High pitch sounds have a short wavelength• Low pitch sounds have a long wavelength.

What is the Doppler Effect?

• The shift in the wavelength produced by a moving source.

• The change in pitch as something approaches you and moves away from you.

LIGHT• Light with a long wavelength will appear red.• Light with a short wavelength will appear blue.

• Approaching light = blue• Leaving light = red

Red Shift• A star or galaxy

moving away from the Earth will produce a shift in its spectrum towards the red end.

Sun Galaxy

Edwin Hubble observed most galaxies in the universe show a red shift.

What does that mean about our Universe?

It’s Expanding!!!

The Big Bang Theory• Red shifts are evidence

supporting the Big Bang.• It’s the dominant scientific

theory about the origin of the universe

• The universe was created sometime ~ 10-20 billion years ago from a cosmic explosion that hurled matter in all directions.