Stars

The Brightness of Stars-Star: A luminous sphere of gas with enormous

mass, that produces energy by fusion.-Fusion: The joining of separate nuclei. Common in

nature, but not on Earth.

Actual vs. Apparent Brightness• Variables which

affect a star’s brightness:

1. Star size2. Distance from Earth3. Star temperature

• Apparent Brightness: The amount of light received on Earth from a star.• Actual Brightness:

How large and hot a star is in relation to other stars.

Star Brightness• Example: Sirius has a

greater apparent brightness then Rigel, even though Rigel is a much hotter and brighter star.• Why?

Lifecycle of Starsvideo: http://www.nationalstemcentre.org.uk/elibrary/resource/5415/the-life-cycle-of-stars

http://www.youtube.com/watch?v=4s7vyDLgk3M

http://www.enchantedlearning.com/sgifs/Starlifecycle.GIF

Star Lifecycle explained

“As space expands there are many more gaps forming and they need to be filled by stars and energy. So stars need to have a dynamic life cycle. Moments of birth and death, right? ”

http://library.thinkquest.org/C0110277/stars/life_cycle1.htm

Where are stars born?• Nebula (stellar nursery):

Stars are born in nebulae-- Huge clouds of dust and gas • Dust and gas particles

exert a gravitational force on each other which keeps pulling them closer together.

• Orion Nebula

More Nebulas• As the particles pull

closer together the temperature increases.• At 10,000,000o C

fusion takes place and energy radiates outward through the condensing ball of gas.

• Another view of Orion

Stellar Evolution – A sun-like star

http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/sunlike.shtml

http://t1.gstatic.com/images?q=tbn:ANd9GcT_XJP25-_6XInCs2WJ2x3ramBhnn-tqYRcDHvFfj96_z1LHKO8kw

Huge Stars…

http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/huge.shtml

Giant Stars…

http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/giant.shtml

Nothing (even light) can escape the gravity of a BLACK HOLEVideos:

http://www.space.com/15421-black-holes-facts-formation-discovery-sdcmp.html

http://dsc.discovery.com/tv-shows/other-shows/videos/stephen-hawkings-universe-black-hole-time.htm

http://dsc.discovery.com/tv-shows/other-shows/videos/how-the-universe-works-birth-of-a-black-hole.htm

Hertzsprung-Russell Diagramhttp://aspire.cosmic-ray.org/labs/star_life/hr_diagram.html

Determining a Star’s Temperature• A star’s temperature can be determined by its color.• All objects will glow a different color when heated differently• Colors hottest to coolest: Blue/white yellow orange

red.

Light-Years• Light-year: Distance light travels in one year. (Equal to about

9.5 trillion kilometers)• Approximate distances:

-Sun to edge of solar system = 5.5 light hours-Nearest star (Alpha Centauri) = 4.3 light years-Center to edge of Milky Way = 50,000 light years

The Sun and You

• Our sun is a main sequence star according to the H-R Diagram.• The actual

brightness is average for a star of its average size.

Layers of the Sun• Dense inner core

which is the site of hydrogen fusion.• Radiation zone:

Energy bounces back and forth before escaping.• Convections zone:

Cooler layer of gas that is constantly rising and sinking.

Anatomy of Sun

• Photosphere: Bright source of much of the light we see.• Chromosphere:

Active layer which is home to many significant displays.

Anatomy of Sun

• Corona: Outer layer which is a gradual boundary between sun and space.

Sunspots• Sunspots: Cool dark

areas on the sun’s surface.-First discovered by Galileo-Not permanent features—Will appear and disappear

Cycle of Solar Activity• Cycle of Solar

Activity: 11 year cycle which see number of sunspots change.• Sunspot Maximum:

Time of many large sunspots.• Sunspot Minimum:

Time of few sunspots.

Solar Flares• Solar Flares: Violent

eruptions near a sunspot which suddenly brighten and shoot outward at high speed.

Solar Flares• The interaction of solar flares with Earth’s magnetic field

causes the aurora borealis/ aurora australis (Northern/Southern Lights)

Earth’s Galaxy—and Others• Galaxy: A large group

of stars, gas, and dust held together by gravity.• Milky Way: Our

galaxy which contains about 200 billion stars and many nebulas

• Spiral Galaxies

Earth’s Galaxy—and Others• Galaxies are grouped

together in clusters.• The cluster the Milky

Way belongs to is called the Local Group.• Three types of

galaxies:

• Cluster of galaxies

Elliptical Galaxies• Elliptical Galaxies:

Most common type of galaxy; large three-dimensional football shaped galaxies.

-Contain mostly older and dimmer stars.

Spiral Galaxies• Spiral Galaxies:

Circular galaxies that have arms curve outward from a central hub.• Arms are made up

of stars and dust

• Two spiral galaxies!!

More Spiral Galaxies• Barred spiral

galaxies: Have two spiral arms extending out.

Irregular Galaxies• Irregular Galaxies:

Come in many different shapes and are smaller and less common than elliptical or spiral galaxies.

The Milky Way Galaxy• 100,000 light years in diameter• Our sun orbits the center of the galaxy once every 240 million

years• Probably a barred spiral galaxy• Contains over 200 billion stars