1. A Closer Look at Visible Light
Astronomy – Ch.20

2. The Visible Spectrum
Visible Light is a combination of all colours of light (ROYGBIV)
Each colour has a different wavelength
Red has longest
Violet has shortest
Astronomers use the spectrum from distant stars to learn more about those stars

3. The Visible Spectrum
Spectra allows astronomers to determine which chemical elements are present in the star’s outer layers
Indicates temperature, pressure, magnetic field, condition of gases in the star
Able to tell if the distance between Earth and the star is increasing or decreasing (Red Shift, Blue Shift)

4. Spectroscopes A tool used to separate starlight into its colours
Combination of a PRISM and a tiny viewing TELESCOPE
The prism can separate the light into its different colours
There are several kinds of visible spectra

5. CONTINUOUS SPECTRUM Unbroken band of colours
Shows that its source is sending out light of all visible wavelengths
Can come from 3 different materials:
A glowing solid (ex: light bulb)
A glowing liquid (ex: molten iron)
A hot compressed gas deep inside a star

6. Bright-line spectrum
Unevenly spaced series of lines of different colours and brightness
The bright lines show that the source is sending out light in certain wavelengths
Comes from chemical elements when they are a gas or vapor
Each element has its own unique bright-line spectrum
Ex: Neon gas in a Neon Sign

7. Dark-Line spectrum
Continuous spectrum with dark lines where light is absorbed
The dark lines are in exactly the same place as the bright lines from the bright-line spectrum
Forms when the light from a continuous spectrum passes through a cooler gas

8. The doppler effect
As an ambulance approaches, the wavelengths shorten and the pitch rises
As it recedes, the wavelengths become longer and the pitch lowers
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9. The doppler effect and light
The distance between a star and Earth can be increasing or decreasing - increasing distance – wavelengths are longer - this causes a RED shift in the star’s spectral lines - decreasing distance – wavelengths are shorter - this causes a BLUE shift in the star’s spectral lines
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