1. Earth Science Ch. 24
The Sun

2. 24.1 The Study of Light

4. 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

5. 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

7. 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

8. 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)

10. 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

12. 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

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

15. 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.

17. 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

18. 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

19. 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

21. 24.3 The sun The sun is the Earth’s primary source of energy
Compared to other stars the sun is an average star

22. 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

23. 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

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

25. 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

27. 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

28. 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.

29. 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

30. 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.

32. 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.