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