A Closer Look at Visible Light Astronomy – Ch.20

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

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)

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

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

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

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

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 Labels

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 Slide for email