Science 9: Unit E: Space Science 9: Unit E: Space ExplorationExploration

Topic 3: Spectroscopy and the Topic 3: Spectroscopy and the Doppler ShiftDoppler Shift

White Light is Made of a Spectrum White Light is Made of a Spectrum of Colours.of Colours.

White light is made up of a spectrum White light is made up of a spectrum of colors. The spectrum of colors of colors. The spectrum of colors starts with red, orange, yellow, starts with red, orange, yellow, green, blue, indigo, and violet/purple. green, blue, indigo, and violet/purple. A spectroscope is a device used to A spectroscope is a device used to show the spectrum of colors given off show the spectrum of colors given off by a light source. It works by having by a light source. It works by having the light pass through a series of the light pass through a series of prisms which break up the light into prisms which break up the light into colors.colors.

Dark Line SpectrumDark Line Spectrum

When a spectroscope was place in When a spectroscope was place in the path of sunlight it was discovered the path of sunlight it was discovered that sunlight did not give off a that sunlight did not give off a continuous spectrum. There were continuous spectrum. There were dark gaps in the sun’s light dark gaps in the sun’s light spectrum. These lines or were called spectrum. These lines or were called spectral lines.spectral lines.

Element SpectraElement Spectra

Two German scientists Kirchoff and Two German scientists Kirchoff and Bunsen discovered that by heating Bunsen discovered that by heating elements until they glowed elements until they glowed (incandescence) they gave off a (incandescence) they gave off a spectrum of their own. A particular spectrum of their own. A particular element gives its own signature element gives its own signature spectrum with its own spectra lines.spectrum with its own spectra lines.

Spectral AnalysisSpectral Analysis Every star gives off its own signature Every star gives off its own signature

spectrum. What makes the spectrum spectrum. What makes the spectrum unique is the position of the spectral lines unique is the position of the spectral lines in the spectrum. in the spectrum.

Just like stars, elements, when heated, Just like stars, elements, when heated, give off their own signature spectrums, give off their own signature spectrums, with their own particular pattern of with their own particular pattern of spectral-lines.spectral-lines.

The location of the spectral lines tells us The location of the spectral lines tells us what elements are in the star. By what elements are in the star. By matching the pattern of spectral lines matching the pattern of spectral lines coming from a star to the known spectral coming from a star to the known spectral patterns of elements you can determine patterns of elements you can determine the composition of a star.the composition of a star.

Doppler Effect, Big Bang, and Doppler Effect, Big Bang, and Red/Blue ShiftRed/Blue Shift

Astronomers noticed that distant Astronomers noticed that distant stars and galaxies gave off spectral stars and galaxies gave off spectral patterns of their own which matched patterns of their own which matched known elements. However, the known elements. However, the patterns were all shifted to the red patterns were all shifted to the red end of the spectrum. At first no one end of the spectrum. At first no one knew what this meant.knew what this meant.

Sound and the Doppler EffectSound and the Doppler Effect When a source of When a source of

sound, like a police sound, like a police siren, moves towards siren, moves towards an observer, the an observer, the waves bunch up and waves bunch up and the sound goes higher the sound goes higher in pitch.in pitch.

When the police car When the police car moves past and away moves past and away from you, the sound from you, the sound waves spread out and waves spread out and the sound goes lower the sound goes lower in pitch.in pitch.

Light and the Doppler EffectLight and the Doppler Effect The same thing happens with light. When The same thing happens with light. When

a light source moves away from you, the a light source moves away from you, the light waves shift to the red end of the light waves shift to the red end of the spectrum (lower frequency), when the spectrum (lower frequency), when the light source moves towards the observer light source moves towards the observer the light waves shift to the blue end of the the light waves shift to the blue end of the spectrum (higher frequency).spectrum (higher frequency).

So What does this mean?So What does this mean? The fact that the spectral lines are all The fact that the spectral lines are all

shifted to the red end of the spectrum shifted to the red end of the spectrum meant that the stars/galaxies and us are meant that the stars/galaxies and us are moving away from each other.moving away from each other.

The Doppler Effect and the The Doppler Effect and the Big Bang TheoryBig Bang Theory

Scientists then theorized that if we’re all Scientists then theorized that if we’re all moving away from each other that we moving away from each other that we must have started out together which must have started out together which gave us the Big Bang Theory. Everything gave us the Big Bang Theory. Everything in the universe started in a tiny point of in the universe started in a tiny point of space and then exploded apart, the Big space and then exploded apart, the Big Bang. We’re still exploding now, Bang. We’re still exploding now, eventually the universe like an elastic-eventually the universe like an elastic-band will stop going out and eventually band will stop going out and eventually start pulling back in to that same point in a start pulling back in to that same point in a Big Crunch.Big Crunch.

Types of SpectraTypes of Spectra

I. Emission/Bright Line Spectra – A I. Emission/Bright Line Spectra – A series of bright colored lines series of bright colored lines produced against a black produced against a black background. These spectra are background. These spectra are produced when a gas is heated at produced when a gas is heated at low/normal pressure. The easiest low/normal pressure. The easiest to produce and see.to produce and see.

Types of Spectra Continued.Types of Spectra Continued.

II. Continuous Spectrum – The full II. Continuous Spectrum – The full spectrum that you see in the spectrum that you see in the rainbow. These are produced when rainbow. These are produced when a gas is heated at high pressure or a gas is heated at high pressure or a solid or liquid is heated.a solid or liquid is heated.

Types of Spectra ContinuedTypes of Spectra Continued

III. Absorption/Dark Line Spectra – III. Absorption/Dark Line Spectra – The kind of spectra we’ve been The kind of spectra we’ve been studying. The continuous spectrum studying. The continuous spectrum with a series of dark gaps (spectral with a series of dark gaps (spectral lines). These are produced when a lines). These are produced when a gas is heated at high pressure and gas is heated at high pressure and then has to pass through a much then has to pass through a much cooler environment. cooler environment.

Diffraction GratingsDiffraction Gratings

A piece of transparent materials (such as A piece of transparent materials (such as plastic or glass) with thousands of closely plastic or glass) with thousands of closely spaced slits in it. This allows light waves to spaced slits in it. This allows light waves to bend around the edges and interfere with bend around the edges and interfere with each other producing areas of constructive each other producing areas of constructive interference (bright lines) and destructive interference (bright lines) and destructive interference (black gaps).interference (black gaps).

Modern spectroscopes use diffraction Modern spectroscopes use diffraction gratings instead of prisms because they gratings instead of prisms because they produce much better detail in showing produce much better detail in showing spectral lines from star spectra.spectral lines from star spectra.