The Sun and Other Stars Notes
(Chapter 30, Section 1, 2, 3 in Glencoe Text)
BMs
E1.2E
Evaluate the future career and occupational prospects of science fields.
E2.2A
Describe the Earth’s principal sources of internal and external energy (e.g.,
radioactive decay, gravity, solar energy).
E5.2A
Identify patterns in solar activities (sunspot cycle, solar flares, solar wind)
E5.2B
Relate events on the Sun to phenomena such as auroras, disruption of radio and
satellite communications, and power grid disturbances
E5.2C
Describe how nuclear fusion produces energy in the Sun
E5.2D
Describe how nuclear fusion and other processes in stars have led to the formation
of all other chemical elements
E5.2e
Explain how the Hertzsprung-Russell (H-R) diagram can be used to deduce other
parameters (distance)
E5.2f
Explain how you can infer the temperature, life span, and mass of a star from its
color. Use the H-R diagram to explain the life cycle of stars.
E5.2g
Explain how the balance between fusion and gravity controls the evolution of a
star (equilibrium).
E5.2h
Compare the evolution paths of low, moderate and high mass stars using the H-R
diagram.
Largest object in the solar system
93,000,000 miles away from earth
Careers (E1.2E)
Astronomer- scientists who study processes and objects in space, such as the Sun and other stars.
Solar Energy (E2.2A)
Earth’s primary source of external (renewable) energy
Provides external heat and light
Affects many of Earth Systems and Spheres
Atmosphere- drives wind and weather patterns; drives the water cycle
Biosphere- drives photosynthesis
Hydrosphere- drives ocean (wave) circulation (unequal heating puts oceans in motion)
Sun’s Atmosphere
First (innermost) layer called the photosphere- visible layer of the sun
Emits most amount of light from the sun (explains why its visible)
400 km (248 miles) thick
Avg. temp. is 5800 K (9980º F)
Second layer called the chromosphere- appears red
2500 km (1553 miles) thick
Avg. temp. is 30,000 K (53,540 º F)
Only visible during solar eclipse when photosphere is blocked
Where solar flares occur
Third (outermost) layer called the corona
Several million (over 600,000 miles) km thick
Avg. temp between 1 million and 2 million K (2,699,540 ºF)
Can only be seen using special instruments or during an eclipse
Solar Activity (E5.2A)
Sunspots- dark spots on the surface of the photosphere
Cooler than surrounding areas of the sun
Located in regions where sun’s magnetic fields poke through the photosphere
These magnetic fields prevent hot gases from escaping and heating the sunspots
Two parts:
Lighter outer ring = penumbra
Darker inner ring = umbra
They last two months and occur in pairs with opposite magnetic polarities (N/S like bar
magnet)
More sunspots = heavier doses of radiation
Solar Activity Cycle
Lasts 11.2 years- maximum number of sunspots
When taking into account the change in Sun’s polarity, cycle is 22.4 years
When sun’s magnetic poles reverse, polarities of sunspots also reverse
Solar maximum = a LOT of sunspots = greater amount of radiation
Greater occurrence of solar flares
Solar minimum = very FEW sunspots = less amount of radiation
Solar Wind
The collective mass of gas flowing outward from the corona (at high speeds- close to one million
mph)
Charged particles (called ions)
Get trapped into earth’s magnetic fields in two huge rings called Van Allen Belts
Our magnetosphere protects us from these winds
These high-energy particles mix with earth’s atmospheric gases and give us the aurora
(such as the Northern Lights)- easily viewed from the Poles
Travels at about 400 miles per second
Because sun rotates (approx. once every 27 days), solar winds are spiraled all throughout
the solar system. No real pattern- steady throughout 27 day rotation period.
Solar Flares
Solar Flares are more common during solar maximum (near sunspots)
Sudden, violent eruptions of particles and radiation from the surface of the sun
Coronal Mass Ejections (CMEs)- huge, fast clouds of gas
Escape in solar winds and can bombard Earth with these particles days later
3-D images of the sun taken by space crafts such as STEREO have greatly enhanced our ability
to follow solar storms and forecast arrival time (so we can prevent as much damage as possible).
How Solar Activity Affects Earth (E5.2B) (E2.2A)
Bad
Coronal Mass Ejections (CMEs) or solar flares can disrupt radio signals, satellites, radar, and cell
phones. They can also damage power stations and cause electrical blackouts.
** NOTE- The Japanese spacecraft, Yokoh, can detect a darkening of the sun’s corona,
which indicates a huge solar storm (or blast) is about to occur. This info can let humans
know to protect or shut down their power grids and protect them from an overload of
solar electricity.
** 1989- Quebec, Canada- Massive blackout lasted over 9 hours, affecting over 6 million
people. This was believed to be caused by an increase in sunspot activity.
Massive solar winds/flares can kill astronauts in space.
Can affect Weather and Climate
Global Warming is in part to changes in solar activity
WARMER during times of high solar activity
COLDER during periods of low solar activity
(Graphs indicate evidence in correlation between solar activity and Global
Warming)
Scientists theorize that during unusually long periods of low sunspot activity, that caused some
ice ages
Good
Solar Energy is one of the Earth’s main sources of external energy (E2.2A)
Warms the earth; activates photosynthesis; drives the water cycle (evaporation and
precipitation)
Solar Flares cause the aurora (northern and southern lights)
Solar Flares send charged particles which excite air molecules in the Earth’s upper
atmosphere
Much like neon lights work
The Solar Interior
Three zones
Core- where fusion takes place; hydrogen and helium
Radiative zone- energy from core is radiated from particle to particle
Convective Zone- energy from radiated particles rises outward
Nuclear Fusion in the Sun (E5.2C)
Pressure and Temperature are very high (needed) = causes fusion
Nuclear Fusion- combining lightweight nuclei into heavier nuclei
2 H atoms collide and fuse  proton-neutron pair (Deuterium) fuses with another H
proton to form 2 proton, 1 neutron nucleus (Tritium)  two 2 proton, 1 neutron pairs
(Tritium) fuse and two protons are released, forming a helium nucleus with 2 protons and
2 neutrons
Mass of Hydrogen is lost and converted into (solar) energy, causes sun to shine and gives
it its high temperature.
E = mc2
Sun is about half way through its fusing process, with about 5 billion years left to go
Fusion and The Formation of New Elements (E5.2D)
Nuclear Fusion and Cooling of Nebula (chemical reactions) lead to the formation of chemical
elements
Temperature must be hot enough for fusion to occur (which is why it can only take place
in the Sun’s core.) The hotter the star, the more fusion can take place.
As temperature changes in a star’s core, fusion can produce different elements
As temperature increases (due to contraction) 
Hydrogen  Helium  Carbon  Oxygen  Neon  Magnesium  Silicon  Iron
Sun only gets to the Carbon burning stage
The hotter the star, the more elements can be produced
The more massive the star, the more elements can be produced
Once a star fuses to the Iron stage, they require more energy rather than release it.
One at a time, neutrons slam into atomic nuclei and subsequently decay into protons by releasing
electrons.
When stars explode (supernova), they emit a lot of energy, much of which can be used to fuse
iron into heavier elements, like Gold and Uranium.
Sun’s Life Cycle
As sun gets older:
Density increases; internal temperature increases; size increases
Roughly 10 billion years- time it takes to fuse all the hydrogen into helium
Sun has been burning hydrogen for approximately 5 billion years, so there is
about 5 billion years left.
Sun Technology
Solar and Heliospheric Observatory (SOHO)- satellite used to observe the Sun.
Using the Hertzsprung-Russell Diagram
(Chapter 30, Section 2)
To Determine Distance (E5.2e)
Hertsprung-Russell Diagram plots luminosity (brightness) or absolute magnitude against their
surface temperature
Shows stages of life of a star
Hot and young
Cold and old
Luminosity- the amount of energy an object in space radiates each second in all directions.
Apparent magnitude- how bright a star appears to be
Remember- the closer a star is, the brighter it appears
Absolute magnitude- how bright a star actually absolutely is
Lower the number, the brighter it is (negative numbers indicate incredibly bright stars)
EX: Sun has apparent magnitude of -26.7, but an absolute magnitude of only +4.8
Astronomers can calculate distance to a star (from earth) by taking the difference between
absolute magnitude and apparent magnitude (distance measured in parsecs)
D = 10(m-M+5)/5
D: distance; m: apparent magnitude;
M: absolute magnitude
One parsec = 3.258 light years
Using Color to Determine Temperature, Life Span and Mass of a Star (E5.2f)
Pneumonic Device: Boys Wear Yellow Overalls Regularly
Color
Blue
White
Yellow
Orange
Red
Temperature
Hottest (9500° C)
Mass
Highest
Life Span
Shortest
Coolest (3900° C)
Lowest
Longest
Spectral Type
O
Be
A
Fine
Girl
Kiss
Me
Mass
Highest
Temperature
Hottest
Luminosity
Brightest
Lowest
Coolest
Dimmest
* Remember: the larger the object, the stronger it’s gravitational force
- High mass stars have a stronger gravitational force, so it takes longer to burn fuel, so they have
a shorter life span.
- Low mass stars have a weaker gravitational force, so it takes longer to burn fuel, so they have a
shorter life span.
The Life Cycle of Stars (E5.2f)
1. BEGINS as nebula in lower right hand corner.
2. Gets hotter and brighter (more luminous) to become protostar.
3. Gets even hotter, but dimmer (less luminous) to become a main sequence star.
4. Gets cooler and brighter (more luminous) to become a Red Giant.
5. Gets hotter and slightly dimmer to become a variable star.
6. Gets hotter and dimmer to become a planetary nebula.
7. Gets cooler and dimmer to become a white dwarf.
8. Gets cooler and dimmer to become a black dwarf.
90% of all stars are main sequence stars (follow the band from top left to bottom right)
- all are fusing hydrogen into helium
Giant stars (above the main sequence)
More luminous
Diameter 10-100 times greater than our Sun
Super Giants (above the giants)
Much more luminous (though relatively cool)
Diameter more than 100 times greater than our Sun
White dwarfs (below main sequence)
Near end of their life
Were once red giant stars that lost outer atmosphere and are now a glowing core
The Balance between Fusion and Gravity Controls the Evolution of a Star (E5.2g)
A “fetal protostar” must reach critical core temperature (15,000,000° C) to continue life cycle.
If reached, it is considered a protostar and begins to fuse hydrogen into helium.
If NOT reached, it becomes brown dwarf and dies (never becomes an official star)
Internal Fusion Force vs. External Gravitational Force
Nuclear fusion releases energy which causes a star to expand (outward). At the same time,
gravitational forces (of outer matter) are putting (inward) pressure on a star, causing it to
contract. This balance is known as hydrostatic equilibrium.
Accretion is the process of adding atoms to the nucleus of a star.
This combination of inward and outward forces keeps a star at equilibrium (outward and inward
forces are in balance). This occurs when star is on the main sequence.
Eventually the hydrogen runs out and star begins to burn helium and star expands (red
giant).
When the fusion process stops, the star dies as gravitational pressure compresses inward
and causes a star to collapse under its own weight.
Low- to moderate-massed stars die easily, commonly as a white dwarf.
High-massed stars die violently in a supernova explosion.
Comparing Evolution Paths of Low, Moderate, and High Mass Stars (E5.2h)
** Key is looking at its placement on the main sequence
Low mass stars- (ex: red dwarfs) less than 1 solar mass; long lifespan; relatively dim (low
luminosity); relatively cool temperatures; burn hydrogen so slowly that they can go on forever
A small, cool star uses up its hydrogen more slowly than the larger stars. It begins its life
like all stars, as a nebula. Then it becomes a protostar and once fusion begins, it becomes
a main sequence star. It can stay at this stage for billions of years. When it has used up all
its hydrogen, it will shrink and become a white dwarf.
Life Cycle of a Low Mass Star
nebula  protostar  main sequence star  white dwarf
Moderate (Medium) mass stars- 1-5 solar masses; average lifespan; average brightness
(luminosity); average temperature; remain on the main sequence (i.e. the Sun) for about 10
billion years; can remain the same size for millions to billions of years;
A medium mass star, like our sun, burns its hydrogen more quickly than a low mass star.
It, like the low mass star, starts life out as a nebula, then becomes a protostar. After
fusion begins, it enters its time on the main sequence. A medium mass star will spend
around 10 billion years as a main sequence star. When a medium mass star runs out of
hydrogen, it will use the hydrogen in its outer layers for fuel. This temperature increase
causes the star to swell into a Red Giant. The burning of hydrogen in the outside layers
causes the expansion while the core is actually shrinking. When it becomes a red giant, it
will swell its diameter from 10 to 1,000 times its original size. Once all the hydrogen is
used up in the star, the pressure in the shrinking core will cause the nuclear reactions
between the helium nuclei in the star. At this point, the inner core stops contracting, and
the outer layers begin to contract, eventually shrinking into a white dwarf. Sometimes
when a larger medium mass star collapses, it will flare up brightly for a few weeks as it
blows its outer layer of gas and dust into space. This is called a planetary nebula.
Life Cycle of a Moderate Mass Star
Nebula  protostar  Red Giant  (Planetary Nebula)  White Dwarf
High mass stars- (8x the mass of Our Sun); short lifespan; very bright (high luminosity); high
temperature; Hydrogen runs out, fusion continues until iron nuclei are formed; star swells to
more than 100 times the diameter of the sun, becoming a super giant.
A high mass star begins its life like the low and medium mass stars. Its starts as a nebula,
then becomes a protostar, and then a main sequence star. Because a high mass star burns
hydrogen quickly, its life span is millions of years instead of billions. After quickly
exhausting its hydrogen supply, a high mass star quickly expands to become a Super
Giant. A super giant can be 500 times the size of our sun. Because it is so large, the core
continues to heat up and use other elements as its fuel. After heating to such a high
temperature, the star then explodes into a supernova. A supernova is one of the most
violent things to happen in the universe. Afterwards, the star will collapse into a neutron
star or black hole. A black hole will occur when an extremely massive star collapes into a
matter that is so dense that light cannot even escape. Astronomers believe that the
elements released during the collapse of a supernova are the source of the elements for
planets and life.
Life Cycle of a High Mass Star
nebula  protostar  main sequence star  Super Giant  supernova  neutron star OR black hole
Finer Points
Iron nuclei don’t release energy (like hydrogen), instead they absorb energy.
Iron core quickly and suddenly collapses; producing a shock wave that blasts the
star’s outer layers into space at thousands of miles per second, and produces a
brilliant burst of light- called a supernova.
Produces many elements, including copper, uranium, silver, and lead.
These elements are blown away into space as a huge cloud of gas and
dust, mixing with what was already there (this is how galaxies and solar
systems form).
After a star goes supernova, it leaves behind its core- a neutron star.
This star is named this way because the gravitational force is so great that each
atom’s electrons are crushed into the nucleus.
A neutron star is for the most part a dense mass of neutrons. While neutron stars
are typically about 20 km in diameter, they are trillions of times more dense than
the sun.
At first, neutron stars spin rapidly, giving off bursts of radio waves and
send beams of radiation through space (like a searchlight).
Astronomers call these rapidly spinning neutron stars a pulsar (because of
the pulses of energy).
A black hole is the remnant of a star at least 15 times as massive as the sun
Source of strong X-Rays; thought to be at the center of the Milky Way Galaxy
Comparing Different Masses of Stars
Mass
Lifespan
Luminosity
Temperature
Long
Low (dim)
(relatively) cool
Low
Average/moderate
Moderate Moderate Moderate
Short
High (bright)
(relatively) hot
High
Links
Stellar Activities (Online)
http://cas.sdss.org/dr6/en/proj/basic/
General Sun Info
How the Sun Works
http://science.howstuffworks.com/sun.htm
Tutorial and Animated Info about the Sun
http://www.windows.ucar.edu/tour/link=/sun/sun.html
Atmosphere and General Info
http://www.solarviews.com/eng/sun.htm
Solar Energy (E2.2A)
How sun affects Earth
http://www.windows.ucar.edu/tour/link=/sun/effect_on_earth.html
How Sun affects weather
http://www.members.shaw.ca/flameball/How%20the%20sun%20makes%20weather.html
Solar Activity (E5.2A)
Solar Activity and Conditions
Gives current solar activity
http://www.sec.noaa.gov/today.html
http://nsosp.nso.edu/data/latest_solar_images.html
Sunspots
Gives current solar conditions and sunspots
http://www.spaceweather.com/
GREAT Sunspots website
http://sohowww.nascom.nasa.gov/sunspots/
Sunspot Cycle (Solar Maximum and Solar Minimum)
http://www.windows.ucar.edu/tour/link=/sun/activity/sunspot_cycle.html&edu=high
http://www.exploratorium.edu/sunspots/
Sunspot Data (from Australian Observatory)
http://www.ips.gov.au/Solar/1/6
Solar Activity Assignments
Solar Activity Online Assignment
http://solar.physics.montana.edu/ypop/Classroom/Lessons/Cycles/
Sunspot Online Activity
http://www.phschool.com/science/planetdiary/background/astracti.html
http://solar.physics.montana.edu/YPOP/Classroom/Lessons/Sunspots/
Animations and Pics of Solar Activity
http://www.windows.ucar.edu/tour/link=/sun/sun_il.html#movies
Cause of Aurora Pic
http://z.about.com/d/weather/1/0/q/-/-/-/What_causes_aurora.gif
http://www.nasa.gov/images/content/147502main_aurora_causes_large.gif
Solar Wind
http://csep10.phys.utk.edu/astr162/lect/sun/wind.html
http://helios.gsfc.nasa.gov/sw.html
Current Solar Wind Conditions
http://space.rice.edu/ISTP/dials.html
Solar Images
Latest SOHO Images
http://sohowww.nascom.nasa.gov/data/latestimages.html
Picture/Grid of Sun (lat/long)
http://solar-center.stanford.edu/images/sungrid-0.gif
Solar Interior
http://ircamera.as.arizona.edu/NatSci102/lectures/suninterior.htm
http://csep10.phys.utk.edu/astr162/lect/sun/interior.html
Solar Activity Affects the Earth (E5.2B)
Quebec Blackout 1989
http://www.windows.ucar.edu/spaceweather/blackout.html
Nuclear Fusion in the Sun (E5.2C)
http://www.universetoday.com/guide-to-space/the-sun/fusion-in-the-sun/
http://fusioned.gat.com/images/pdf/what_is_fusion.pdf
http://zebu.uoregon.edu/~soper/Light/fusion.html
Fusion Drawing
http://www.ifa.hawaii.edu/~barnes/ast110_06/tsaas/FusionintheSun.png
Fusion Animation
http://zebu.uoregon.edu/textbook/energygen.html
http://www.atomicarchive.com/Movies/Movie5.shtml
http://www.windows.ucar.edu/tour/link=/sun/Solar_interior/Nuclear_Reactions/Fusion/Fusion_in_stars/H_fusion.html
COOL Hydrogen Fusion in the Sun (short) Computer Demo
http://www.astro.ubc.ca/~scharein/a311/Sim/fusion/Fusion.html
Supernova Explosion
http://library.thinkquest.org/25763/supernova.htm
Formation of Chemical Elements in Space (E5.2D)- GOOD ARTICLE
http://library.thinkquest.org/C003763/index.php?page=origin03
http://astrophysics.suite101.com/article.cfm/origin_of_the_chemical_elements
http://son.nasa.gov/tass/content/article1.htm
GOOD Info and charts and graphs
http://imagine.gsfc.nasa.gov/docs/teachers/elements/
GOOD BOOK on Stellar Evolution (can preview on Google Books)
Strickberger's Evolution: The Integration of Genes, Organisms and Populations
By Brian Keith Hall, Benedikt Hallgrímsson, Monroe W. Strickberger
Edition: 4, illustrated
Published by Jones & Bartlett Publishers, 2007
ISBN 0763700665, 9780763700669
760 pages
Motions of Celestial Bodies and Their Effects
http://www.sciencemaster.com/space/item/motions.php
Hertzsprung-Russell (H-R) Diagram to Deduce other Parameters (Distance) (E5.2e)
http://www.synapses.co.uk/astro/hrdiag.html
Star’s Color to Infer Temperature, Life Span, Mass (E5.2f)
http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml
http://nix.ksc.nasa.gov/info;jsessionid=wrqwwqpiam3k?id=GL-2002-001195&orgid=6
http://jumk.de/astronomie/about-stars/index.shtml
Using the Hertzsprung-Russell (H-R) Diagram
GOOD info and GREAT Interactive Lab (using computer)
http://aspire.cosmic-ray.org/labs/star_life/hr_diagram.html
http://www.virtualobservatory.org/explorer/proj/teachers/advanced/hr/background.aspx
Info
http://www.wncc.net/courses/aveh/lecture/lecmeas.htm
Using the Hertzsprung-Russell (H-R) Diagram to Determine Life Cycle of a Star (E5.2f)
Info and pics on Life Cycle of a Star
http://cas.sdss.org/dr6/en/astro/stars/images/track.jpg
http://aspire.cosmic-ray.org/labs/star_life/starlife_main.html
http://skyserver.sdss.org/dr1/en/astro/stars/stars.asp
http://cornwallastro.info/m4u3a4
GOOD Info on the life cycle of a star
http://curious.astro.cornell.edu/question.php?number=38
Life Cycle of the Sun
http://skyserver.sdss.org/dr1/en/astro/stars/images/starevol.jpg
PIC of evolutionary path
http://www.astro.bas.bg/~petrov/herter00_files/lec19_02.gif
Interactive Animation of the HR Diagram
http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html
http://aspire.cosmic-ray.org/labs/star_life/support/HR_animated_real.html
Colored Picture of the H-R Diagram
http://www.murryclan.us/nsg/hr_diagram.jpg
Protostar Pic on HR
http://boojum.as.arizona.edu/~jill/NS102_2006/Lectures/Starformation/17-06.jpg
Stellar Evolution (E5.2f, E5.2g, E5.2h)
http://cass.ucsd.edu/public/tutorial/StevI.html
http://physics.uoregon.edu/~jimbrau/astr122/Notes/Chapter20.html
http://physics.uwyo.edu/~stark/outreach/StarLives/life+death/
GREAT pic of Stellar Evolution and How Mass dictates
http://www.siprep.org/faculty/aokeefe/images/stellarevolutionstellar_fate_type1a_label_300dpi.jpg
Interactive Lesson
http://www.ioncmaste.ca/homepage/resources/web_resources/CSA_Astro9/files/html/module2/module2.html#6
Animation
http://www.eram.k12.ny.us/education/components/docmgr/default.php?sectiondetailid=17500&f
ileitem=637&catfilter=452
Stellar Evolution and Equilibrium (E5.2f, E5.2g, E5.2h)
http://www.umich.edu/~gs265/star.htm
Pic of Hydrostatic Equilibrium
http://lasp.colorado.edu/education/outerplanets/images_solsys/big/sun_equilibrium.jpg
Stellar Evolution Questions (E5.2f, E5.2g, E5.2h)
http://webs.wichita.edu/astronomy/Testbank/evol.htm
Life Cycle of Low, Moderate, and High Mass Stars (E5.2h)
http://schoolscience.rice.edu/science/curricula/PrintPreviewLearningExperienceOnly.cfm?LEID=2030&CurriculaID=317
http://www.astro.keele.ac.uk/workx/starlife/StarpageS_26M.html
Comparing Evolution of Stars with different masses (E5.2h)
Animation of low mass star on HR diagram (E5.2h)
http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html
Animation of HIGH MASS star exploding as a supernova
http://www.nasa.gov/multimedia/imagegallery/image_feature_560.html
HR Diagram of high mass star (20 solar masses) (E5.2h)
http://www.astro.bas.bg/~petrov/herter00_files/lec19_03.gif
GREAT website with animations on evolution of masses
http://rainman.astro.uiuc.edu/ddr/stellar/beginner.html