Chapter 8Chapter 866thth Grade Grade

Section 1Section 1Stars are huge, bright balls of gas trillions Stars are huge, bright balls of gas trillions of kilometers away. of kilometers away.

Stars have different colors so they must Stars have different colors so they must have different temperatures. have different temperatures.

Stars are made up of gas. The inner layer Stars are made up of gas. The inner layer of a star is very dense and hot. The outer of a star is very dense and hot. The outer layers are made up of cooler gases. layers are made up of cooler gases. Different elements absorb different Different elements absorb different wavelengths of light so astronomers can wavelengths of light so astronomers can tell what elements a star is made of. tell what elements a star is made of.

Section 1Section 1Look through a prism you see a spectrum of Look through a prism you see a spectrum of colors. Fire gives off a spectrum. colors. Fire gives off a spectrum.

Astronomers use an instrument called a Astronomers use an instrument called a spectrograph to break a starspectrograph to break a star’’s light into a s light into a spectrum. This gives the astronomers spectrum. This gives the astronomers information about the stars composition information about the stars composition and temperature. and temperature.

When an element emits light only certain When an element emits light only certain colors show up. The colors are called colors show up. The colors are called emission lines----kind of like fingerprints. emission lines----kind of like fingerprints.

http://sciencestage.com/v/617/burning-http://sciencestage.com/v/617/burning-salt-metal-ion-chemistry-demo-salt-metal-ion-chemistry-demo-demonstration-flame-test-russia-sully-demonstration-flame-test-russia-sully-sully-russia-color-colored.htmlsully-russia-color-colored.html

Section 1Section 1A star has both bright and dark emission A star has both bright and dark emission lines. The stars atmosphere absorbs certain lines. The stars atmosphere absorbs certain colors of light in the spectrum, which causes colors of light in the spectrum, which causes black lines to appear in the emission lines. black lines to appear in the emission lines.

Absorption spectrum is produced when light Absorption spectrum is produced when light from a hot solid or dense gas passes from a hot solid or dense gas passes through a less dense, cooler gas. The through a less dense, cooler gas. The cooler cooler gas gas absorbs certain portions of the absorbs certain portions of the spectrum. Since some of the spectrum is spectrum. Since some of the spectrum is absorbed sorting the elements is often absorbed sorting the elements is often difficult. difficult.

Section 1Section 1Stars were originally classified according Stars were originally classified according to the element composition—1800s. Now to the element composition—1800s. Now stars are classified by temperature. stars are classified by temperature.

Class O stars are blue---the hottest. Class O stars are blue---the hottest. Pg.223. Pg.223.

Originally, astronomers created a system Originally, astronomers created a system to classify stars based on brightness. The to classify stars based on brightness. The brightest stars were first magnitude. The brightest stars were first magnitude. The dimmest stars were sixth magnitude. They dimmest stars were sixth magnitude. They used only their eyes. used only their eyes.

Section 1Section 1They then began to use telescopes and could They then began to use telescopes and could see dimmer stars. They added to the old see dimmer stars. They added to the old system of classifying stars. Positive numbers system of classifying stars. Positive numbers represent dimmer stars and negative represent dimmer stars and negative numbers represent brighter stars. Can see numbers represent brighter stars. Can see as far as the 29as far as the 29thth magnitude. Brightest is magnitude. Brightest is Sirus -1.4—apparent brightness. Sirus -1.4—apparent brightness.

Distance can affect brightness. Sun appears Distance can affect brightness. Sun appears at -26.8 in apparent magnitude but absolute at -26.8 in apparent magnitude but absolute magnitude is +4.8.magnitude is +4.8.

Apparent magnitude: the brightness of a Apparent magnitude: the brightness of a star as seen from Earth. star as seen from Earth.

Section 1Section 1Absolute Magnitude: is the actual brightness of a star. Absolute Magnitude: is the actual brightness of a star.

Because stars are long distances away astronomers use Because stars are long distances away astronomers use light-years to measure the distances from Earth to the light-years to measure the distances from Earth to the stars. stars.

Light year is the distance light travels in one year. Light year is the distance light travels in one year.

Parallax: an apparent shift in the position of an object Parallax: an apparent shift in the position of an object when viewed from different locations. The Earth when viewed from different locations. The Earth moves. Astronomers must use math to figure out the moves. Astronomers must use math to figure out the actual distance. Closer stars seem to move more than actual distance. Closer stars seem to move more than distant stars.distant stars.

The earth faces different stars depending on the time of The earth faces different stars depending on the time of year---b/c of tilt and rotation. Stars move slowly….pg. year---b/c of tilt and rotation. Stars move slowly….pg. 225-226.225-226.

Section 2Section 2A star life cycle: first stage: it is a ball of gas and A star life cycle: first stage: it is a ball of gas and dust. Gravity pulls the dust and gas together into dust. Gravity pulls the dust and gas together into a sphere. As the sphere becomes denser it a sphere. As the sphere becomes denser it becomes hotter. Hydrogen changes to helium by becomes hotter. Hydrogen changes to helium by a process called nuclear fusion. When a star dies a process called nuclear fusion. When a star dies its materials return to space---sometimes to form its materials return to space---sometimes to form new stars. new stars.

Stars can be classified by their size, mass, Stars can be classified by their size, mass, brightness, color, temperature, spectrum, and brightness, color, temperature, spectrum, and age. Can also be classified as main-sequence age. Can also be classified as main-sequence stars, giants, supergiants, and white dwarfs. Can stars, giants, supergiants, and white dwarfs. Can be reclassified later in its life. be reclassified later in its life.

http://didyouknow.org/the-size-of-the-sun-in-http://didyouknow.org/the-size-of-the-sun-in-comparison/comparison/

http://library.thinkquest.org/17940/texts/star/http://library.thinkquest.org/17940/texts/star/star.htmlstar.html

Section 2Section 2Main-sequence stars: after it forms this is Main-sequence stars: after it forms this is the longest stage of its life cycle. During the longest stage of its life cycle. During this stage energy is generated in the core this stage energy is generated in the core of the star as hydrogen atoms fuse into of the star as hydrogen atoms fuse into helium. The fusion releases a lot of energy. helium. The fusion releases a lot of energy. This is where the stars energy comes from. This is where the stars energy comes from. Stays the same size.Stays the same size.

Giants and Supergiants: Third stage of its Giants and Supergiants: Third stage of its life cycle. Red giant: star expands and life cycle. Red giant: star expands and cools once it is out of hydrogen. The center cools once it is out of hydrogen. The center of the star shrinks and the atmosphere of the star shrinks and the atmosphere expands. Red giants can be 10X bigger expands. Red giants can be 10X bigger than the sun and supergiants can be 100X than the sun and supergiants can be 100X bigger. bigger.

Section 2Section 2White Dwarfs: Final stage of a starWhite Dwarfs: Final stage of a star’’s life s life cycle. Can have the same mass as the cycle. Can have the same mass as the sun or smaller. It is a hot star that is sun or smaller. It is a hot star that is just the leftover center of an older star. just the leftover center of an older star. It does not have any hydrogen left and It does not have any hydrogen left and can shine for billions of years before it can shine for billions of years before it cools completely. cools completely.

Section 2Section 2Ejnar Hertzsprung and Henry Norris Ejnar Hertzsprung and Henry Norris Russell developed the H-R diagram Russell developed the H-R diagram independently---their ideas were put independently---their ideas were put together. It shows the relationship together. It shows the relationship between a stars surface temperature between a stars surface temperature and absolute magnitude. It can also and absolute magnitude. It can also show how stars change over time. show how stars change over time.

Read pg. 231….lets talk about it. Read pg. 231….lets talk about it.

Section 2Section 2Large stars may explode and become Large stars may explode and become supernovas, black holes, neutron stars, or supernovas, black holes, neutron stars, or pulsars. pulsars.

Supernovas: Massive stars use hydrogen Supernovas: Massive stars use hydrogen faster than smaller stars. They donfaster than smaller stars. They don’’t tend t tend to have long lives when compared to other to have long lives when compared to other stars. When it explodes it may become a stars. When it explodes it may become a supernova—supernova—a gigantic explosion which a gigantic explosion which throws the stars outer layers into space. It throws the stars outer layers into space. It is so powerful that it can be brighter than a is so powerful that it can be brighter than a galaxy for a day. galaxy for a day.

Section 2Section 2Neutron stars: when gravity is so great Neutron stars: when gravity is so great that protons and electrons smash that protons and electrons smash together to form neutrons. If it is together to form neutrons. If it is spinning it is called a pulsar. It sends spinning it is called a pulsar. It sends out a beam of radiation across space.out a beam of radiation across space.

Black holes: so massive light cannot Black holes: so massive light cannot escape it. They are hard to locate escape it. They are hard to locate because they do not give off light. because they do not give off light.

Section 3Section 3Galaxies: large groups of stars, dust and Galaxies: large groups of stars, dust and gas. Come in all shapes and sizes. gas. Come in all shapes and sizes.

Hubble telescope…who can tell me about it? Hubble telescope…who can tell me about it?

Spiral galaxies: have a bulge in the center Spiral galaxies: have a bulge in the center and spiral arms. The arms are gas, dust, and spiral arms. The arms are gas, dust, and new stars. Pg. 234-235. and new stars. Pg. 234-235.

The Milky Way: astronomers think our The Milky Way: astronomers think our galaxy is a spiral galaxy. It is hard to see galaxy is a spiral galaxy. It is hard to see because of gas and dust.because of gas and dust.

Section 3Section 3Elliptical Galaxies: 1/3 of all galaxies. Look Elliptical Galaxies: 1/3 of all galaxies. Look like blobs or spheres. Usually have bright like blobs or spheres. Usually have bright centers with very little dust and gas. Contain centers with very little dust and gas. Contain mostly old stars---b/c little to no gas to form mostly old stars---b/c little to no gas to form new stars. Two types: giant elliptical new stars. Two types: giant elliptical galaxies and dwarf elliptical galaxies.galaxies and dwarf elliptical galaxies.

Irregular Galaxies: galaxies that donIrregular Galaxies: galaxies that don’’t fit into t fit into any certain category or class. Their shape is any certain category or class. Their shape is irregular. irregular.

http://htwins.net/scale2/http://htwins.net/scale2/

Section 3Section 3Nebula: large clouds of dust or gas. Found mostly in Nebula: large clouds of dust or gas. Found mostly in spiral galaxies but some are found in elliptical spiral galaxies but some are found in elliptical galaxies.galaxies.

Globular clusters: a group of older stars that look Globular clusters: a group of older stars that look like a ball. Could be up to 1 million stars in the like a ball. Could be up to 1 million stars in the cluster. Surrounds spiral galaxies and elliptical cluster. Surrounds spiral galaxies and elliptical galaxies. Located in a spherical halo that surrounds galaxies. Located in a spherical halo that surrounds spiral galaxies. spiral galaxies.

Open cluster: closely grouped stars—few 100 to few Open cluster: closely grouped stars—few 100 to few 1000 in a cluster---usually blue stars. Pg. 236. 1000 in a cluster---usually blue stars. Pg. 236. Usually found in the spiral disk of a galaxy.Usually found in the spiral disk of a galaxy.

Quasars: star like sources of light that are extremely Quasars: star like sources of light that are extremely far away. One of the most powerful energy sources far away. One of the most powerful energy sources in the universe. Thought to be the most distant in the universe. Thought to be the most distant objects in space. objects in space. http://www.phys.vt.edu/%7Ejhs/faq/quasars.html#q2http://www.phys.vt.edu/%7Ejhs/faq/quasars.html#q2

Section 4Section 4Cosmology: The study of the origin, Cosmology: The study of the origin, structure, and development of the structure, and development of the universe. universe.

The universe is expanding….galaxies The universe is expanding….galaxies are moving apart. are moving apart.

Raisin-Bread Model:Raisin-Bread Model:

Big Bang Theory: tremendous Big Bang Theory: tremendous explosion--13.7 billion years agoexplosion--13.7 billion years ago

Section 4Section 4Cosmic background radiation: radiation Cosmic background radiation: radiation found in all directions that scientist found in all directions that scientist believe is left over from the big bang. believe is left over from the big bang.

Scientist believe the universe is a cosmic Scientist believe the universe is a cosmic repetition made up of galaxies, planets, repetition made up of galaxies, planets, stars, etc. stars, etc.

Scientist think the universe will either Scientist think the universe will either continue to expand forever or it will continue to expand forever or it will eventually collapse in on itself—the eventually collapse in on itself—the opposite of expanding. opposite of expanding.