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2.4 Studying the Sun
Electromagnetic Radiation The visible light we see is only a
fraction of energy coming from various objects
Most of what we know about the universe is obtained from the study of light emitted from stars and other bodies
All of the wavelengths of electromagnetic radiation is known as the electromagnetic spectrum
Electromagnetic Radiation
The human eye can only see radiation of wavelengths in the visible light spectrum
Visible light consists of a range of waves, with various wavelengths Demonstrated with a prism
As visible light pass through a prism, the light is refracted (or bent) and separated into its components colors Produces a familiar rainbow of colors (ROYG. BIV)
The longer wavelength colors produces a lower frequency (ex. Red) The shorter wavelength colors produces a higher frequency (ex.Violet)
Telescopes
Telescopes are instruments designed to make distant objects appear nearer, through collection of EM radiation
Telescopes that collect radiation in the visible spectrum are known as optical telescopes
For observing invisible radiation there are telescopes that detect radio waves, gamma rays, x-rays, and every other type of EM radiation
Optical Telescopes
Two types:Refracting – uses lenses to bend or refract light
Suffer a major defect, they bend shorter wavelengths of light more than longer ones
For example, when in focus for red light, blue and violet light are out of focus
Reflecting – uses mirrors to gather and focus lightMost large telescopes are reflectors (ex. Hubble Space Telescope)Can be made very large without reducing the quality of the image
Refracting Telescope
Reflecting Telescope
Based on what you know about prisms and visible light, how do you think rainbows form in Earth’s atmosphere?
Answer: Visible light is bent when it encounters water droplets in the atmosphere and is separated into its component colors
Spectroscopy
The study of the properties of light that depend on wavelength A spectrograph is a device used to separate light into a
spectrum There are three types of spectra, generated under different
conditions Continuous spectrum Absorption spectrum Emission spectrum
When the spectrum of a star is studied, the spectral lines act as “fingerprints” to identify the star’s chemical make-up
Continuous Spectrum
Produced by an incandescent solid, liquid, or gas under high pressure (ex. Common light bulb)
Generates an uninterrupted band of color
Absorption Spectrum
Produced when visible light is passed through a cool gas under low pressure
Gas absorbs some wavelengths of light, so spectrum looks continuous with some dark lines through it
Each element produces a unique set of spectral lines
Emission Spectrum
Produced by a hot gas under low pressure Generates bright lines of certain wavelengths of color, but the rest
is dark
Nuclear Fusion The way our sun and other stars
produce energy This nuclear reaction converts 4
hydrogen atoms into a helium atom Tremendous energy is released
During nuclear fusion, energy is released because some matter is converted into energy
Hydrogen atoms are the primary fuel for fusion in the Sun
Matter into Energy E = mc 2
E = energy m = mass c = the speed of light
This is known as the Theory of Relativity proposed by Einstein It saysthat a small amount of matter
can make a large amount of energy One of the final products of fusion of
Hydrogen in the Sun is always Helium
Matter into Energy
Because the speed of light is very great, the amount of energy released from a small amount of mass is enormous Conversion of one pinhead’s worth of
hydrogen to helium releases more energy than burning thousands of tons of coal
Nuclear fusion not limited to just Hydrogen to Helium In hotter stars than our Sun, energy is
produced by fusion of other elements like Carbon, Nitrogen, and Oxygen
The Structure of the Sun
Sun divided into four parts: The solar interior
Where the energy is produced and moves through The visible surface (photosphere)
Radiates most of the sunlight we see The chromosphere
Just above the photosphere Thin layer of hot gases that appear as a red rim around the sun
The Corona (or Crown) Outermost layer Visible only when the photosphere is covered (total solar eclipse)
How much longer do you think the sun will likely exist in its present state? Answer: The sun is estimated to last easily
another 5 billion years before using up all of its hydrogen fuel