Earth Science Ch. 24 The Sun

24.1 The Study of Light

Spectra of Visible Light Continuous spectrum Uninterrupted band of color Absorption spectrum Cool gas The spectrum appears continuous but with a series of dark lines The type of spectrum produced by stars

Emission spectrum Hot gas Series of bright lines Each element or compound in its gaseous state produces a unique set of spectral lines Spectral lines identify the elements present in a star and thus the star’s chemical composition

The Doppler Effect The perceived change in frequency of a wave that is emitted from a source that is moving away from or toward an object If the source is moving toward an observer, the wavelength decreases and frequency increases If the source is moving away from an observer, the wavelength increases and the frequency decreases

Visible light moving away from an observer appears more red because the wavelength is increased. This is called a red shift. Visible light moving toward an observer appears more blue because the wavelength has decreased. This is called a blue shift Our universe is currently experiencing a red shift (expanding)

24.2 Tools for studying space Refracting Telescope Uses the bending or refracting of light The objective lens produces an image by bending light from a distant object so that the light converges at an area called the focus The eyepiece magnifies the image produced by the objective lens

Reflecting Telescope Use a concave mirror that focuses light in front of the mirror rather than behind it like a lens does Because the focus is in front of the mirror the observer must also be in front of the mirror

Both refracting and reflecting telescopes have 3 properties that aid astronomers: Light gathering power Resolving power: sharper images and finer detail Magnifying power

Radio telescopes The measurement of radio wave radiation is important because it allows astronomers to measure the distribution of hydrogen which is the main material that stars are made of.

Advantages of radio telescopes Much less affected by turbulence, clouds and weather Viewing is possible 24 hours a day They can see through interstellar dust clouds The can detect clouds of gases that are too cool to emit visible light. These clouds are the sites of star formation Disadvantages Hindered by human made radio interference

Radio telescopes have allowed for the discovery of quasars. Quasars are radio wave sources that appear to exist in the center of newly formed galaxies

Space Telescopes The Hubble telescope was the first space telescope The Hubble telescope has 10 billion times more light gathering power than the unaided human eye

24.3 The sun The sun is the Earth’s primary source of energy Compared to other stars the sun is an average star

Structure of the Sun The Solar Interior All energy produced by the sun occurs in this region by the process of nuclear fusion The core The radiation zone The convection zone

Photosphere The light sphere The visible surface of the sun Energy is transferred by convection Rising hot gases increases brightness and sinking cool gases causes the surface to darken Produces an absorption spectrum 90% hydrogen, 10% helium

Chromosphere Thin layer above the photosphere The color sphere Appears as a red rim around the sun Produces an emission spectrum

Corona Outermost portion of the solar atmosphere Only visible when the photosphere is covered such as during a solar eclipse The streams of protons and electrons that flow from the corona make up the solar winds Earth’s magnetic field prevents solar winds from reaching our surface

Activity of the Sun Sunspots Prominences Dark regions on the surface of the sun Appear darker because temperatures are cooler Islands of magnetism floating on the sun’s surface Usually occur in pairs Sunspots appear in 11 year cycles Prominences Huge cloud like structures coming from the chromosphere Often appear as great arches Bases are normally associated with sunspots where they are trapped by magnetic fields

Solar flares Explosive events associated with sunspots After a strong solar flare, earth’s upper atmosphere near its magnetic poles is set aglow causing the auroras or northern lights.

The Solar Interior The sun produces energy by the process of nuclear fusion In nuclear fusion, hydrogen nuclei are converted into the nucleus of a helium atom When fusion occurs tremendous energy is released E = mc2 E: energy, m: mass, c: speed of light Most of the energy is in the form of high energy photons

Just below the photosphere, convection currents transport the energy to the solar surface The energy radiates through the chromosphere and corona The process of fusion of hydrogen to helium produces the energy of the sun.

The sun has enough fuel to last 100 billion years It is thought that the sun can continue its present stable state for about 10 billion years It is believed that the sun is about 4.5 billion years old For nuclear fusion to have started, the sun’s internal temperature had to reach several million degrees This increase in temperature is believed to have happened when the gases in the early solar system were compressed. Temperature increased due to high pressure. The sun was the only body that became hot enough for nuclear fusion to occur.