Stars, Galaxies, and the Stars, Galaxies, and the UniverseUniverse

Section 1Section 1

Tools of Modern AstronomyTools of Modern Astronomy

Constellations: Patterns of stars in the Constellations: Patterns of stars in the sky.sky.

Electromagnetic RadiationElectromagnetic Radiation

Visible light: Light you see with your Visible light: Light you see with your eyes.eyes.

Electromagnetic radiation: Energy that Electromagnetic radiation: Energy that can travel directly through space in the can travel directly through space in the form of waves.form of waves.

Electromagnetic SpectrumElectromagnetic Spectrum Wavelength: The distance Wavelength: The distance

between the crest of one between the crest of one wave and the crest of the wave and the crest of the next wave.next wave.

Spectrum: light that spreads Spectrum: light that spreads out to make a range of out to make a range of different colors with different different colors with different wavelengths.wavelengths.

Electromagnetic spectrum: Electromagnetic spectrum: includes radio waves, includes radio waves, infrared radiation, visible infrared radiation, visible light, ultraviolet radiation, X-light, ultraviolet radiation, X-rays, and gamma rays.rays, and gamma rays.

TelescopesTelescopes Telescopes: Collect and focus different types of Telescopes: Collect and focus different types of

electromagnetic radiation including visible light.electromagnetic radiation including visible light. Convex lens: A piece of transparent glass, curved so Convex lens: A piece of transparent glass, curved so

that the middle is thicker than the edges.that the middle is thicker than the edges. Refracting telescopes: use convex lens to gather a large Refracting telescopes: use convex lens to gather a large

amount of light and focus it into a small area.amount of light and focus it into a small area. Reflecting telescopes: Uses a mirror instead of a lens.Reflecting telescopes: Uses a mirror instead of a lens. Radio Telescopes: Detect radio waves from objects in Radio Telescopes: Detect radio waves from objects in

space.space. Observatory: A building that contains one or more Observatory: A building that contains one or more

telescopes.telescopes.

SpectrographsSpectrographs Spectrograph: Breaks the light from an object into Spectrograph: Breaks the light from an object into

colors and photographs the resulting spectrum.colors and photographs the resulting spectrum.

Astronomers use spectrographs to get information Astronomers use spectrographs to get information about stars, including their chemical compositions about stars, including their chemical compositions and temperatures.and temperatures.

Chemical Composition and Chemical Composition and Temperature of StarsTemperature of Stars

Chemical elements in a star’s atmosphere Chemical elements in a star’s atmosphere absorb light from the star. Each element absorbs absorb light from the star. Each element absorbs light at different wavelengths. Thus by light at different wavelengths. Thus by comparing them to other known spectrums of comparing them to other known spectrums of different elements astronomers can infer which different elements astronomers can infer which elements are found in a star.elements are found in a star.

Chemical composition of stars are about 73% Chemical composition of stars are about 73% hydrogen,25% helium, and 2% other elements. hydrogen,25% helium, and 2% other elements. By comparing a star’s spectrum with the known By comparing a star’s spectrum with the known spectrums of elements at different temperatures, spectrums of elements at different temperatures, astronomers can infer how hot the star is. astronomers can infer how hot the star is.

ReviewReview

For what purpose are telescopes designed?For what purpose are telescopes designed?

Telescopes collect and focus electromagnet Telescopes collect and focus electromagnet radiation.radiation.

What can astronomers tell from looking at a What can astronomers tell from looking at a star’s spectrum?star’s spectrum?

Astronomers can determine the chemical Astronomers can determine the chemical composition and the temperature of the star.composition and the temperature of the star.

Section 2Section 2Characteristics of StarsCharacteristics of Stars

TermsTermsCharacteristics of StarsCharacteristics of Stars

GalaxyGalaxy: Contains hundreds of billions of : Contains hundreds of billions of stars. (Milky Way)stars. (Milky Way)

UniverseUniverse: All of space and everything in : All of space and everything in it.it.

Light-yearLight-year: Distance that light travels in : Distance that light travels in one year. one year. It is a unit of distance not timeIt is a unit of distance not time..

ParallaxParallax: The apparent change in position : The apparent change in position of an object when you look at it from of an object when you look at it from different places.different places.

Classifying StarsClassifying Stars

The main The main characteristics used to characteristics used to classify stars are: classify stars are: Size, Temperature Size, Temperature and Brightness.and Brightness.

Star sizes largest to Star sizes largest to smallest are:smallest are:

Super Giant, Giant, Super Giant, Giant, Medium, White Dwarf, Medium, White Dwarf, and Neutron stars.and Neutron stars.

Color and Temperature of StarsColor and Temperature of Stars

A stars color reveals its temperature. The A stars color reveals its temperature. The coolest stars are red and hottest stars are blue, coolest stars are red and hottest stars are blue, blue-white.blue-white.

The brightness of a star depends upon its size The brightness of a star depends upon its size and temperature.and temperature.

How bright a star looks from Earth depends on How bright a star looks from Earth depends on both how far the star is from Earth and how both how far the star is from Earth and how bright the star actually is. bright the star actually is.

BrightnessBrightness

Apparent magnitude: Apparent magnitude: Is the star’s Is the star’s brightness as seen from Earth. (use brightness as seen from Earth. (use electronic devices to measure it.electronic devices to measure it.

Absolute magnitudeAbsolute magnitude: A brightness a star : A brightness a star would have if it were a standard distance would have if it were a standard distance from Earth.from Earth.

Hertzsprung-Russell DiagramHertzsprung-Russell Diagram

A graph used by A graph used by astronomers that shows astronomers that shows the relationship between the relationship between surface temperature and surface temperature and brightness of stars.brightness of stars.

Most stars (90%) fall under Most stars (90%) fall under the Main Sequence in the Main Sequence in which surface which surface temperatures increases as temperatures increases as brightness increases.brightness increases.

ReviewReview

What is a parallax? How is it useful in astronomy?What is a parallax? How is it useful in astronomy? Parallax is the apparent change in an object’s position Parallax is the apparent change in an object’s position

when viewed from two different places. Astronomers when viewed from two different places. Astronomers can use parallax to calculate distances to nearby can use parallax to calculate distances to nearby stars.stars.

List three characteristics used to classify stars.List three characteristics used to classify stars. Size, temperature (or color) and brightnessSize, temperature (or color) and brightnessWhich is hotter-- a red star or a blue star? Why?Which is hotter-- a red star or a blue star? Why? Blue stars are hotter than red stars because gas glows Blue stars are hotter than red stars because gas glows

red at lower temperatures and blue at higher red at lower temperatures and blue at higher temperatures.temperatures.

Section 3Section 3Lives of StarsLives of Stars

A Star Is BornA Star Is Born NebulaNebula: All stars start out as nebulas. A large : All stars start out as nebulas. A large

amount of gas and dust spread out in an amount of gas and dust spread out in an immense volume.immense volume.

ProtoProto: Greek for “earliest”: Greek for “earliest” ProtostarProtostar: Earliest stage of a star.: Earliest stage of a star. A star is born when the contrasting gas and dust A star is born when the contrasting gas and dust

become so hot that nuclear fusion starts.become so hot that nuclear fusion starts. How long a star lives depends on how much How long a star lives depends on how much

mass it has. (More mass=shorter lives)mass it has. (More mass=shorter lives)

Death of StarsDeath of Stars

When a star runs out of When a star runs out of fuel, it becomes a white fuel, it becomes a white dwarf, a neutron star, or dwarf, a neutron star, or a black hole.a black hole.

When it runs out of fuel When it runs out of fuel the center of the star the center of the star shrinks and the outer shrinks and the outer part of the star part of the star expands.expands.

Terms of StarsTerms of Stars White dwarfWhite dwarf: The remaining hot core of a star after its : The remaining hot core of a star after its

outer layers have expanded and drifted out into space.outer layers have expanded and drifted out into space.

Neutron StarNeutron Star: A tiny star that remains after a supernova : A tiny star that remains after a supernova explosion.explosion.

SupernovaSupernova: The explosion of a dying giant or : The explosion of a dying giant or supergiant star.supergiant star.

Black holeBlack hole: The remains of an extremely massive star : The remains of an extremely massive star pulled into a small volume by the force of gravity.pulled into a small volume by the force of gravity.

ReviewReview

What is the earliest stage in the life of a star?What is the earliest stage in the life of a star?

The star begins as part of a nebula. A cloud of dust and The star begins as part of a nebula. A cloud of dust and gas. Some of the dust and gas condenses to form a gas. Some of the dust and gas condenses to form a protostar. Nuclear fusion begins and the protostar protostar. Nuclear fusion begins and the protostar becomes a star.becomes a star.

Why do small-mass stars have longer lifetimes than Why do small-mass stars have longer lifetimes than large-mass stars?large-mass stars?

Small-mass stars burn their fuel more slowly than large-Small-mass stars burn their fuel more slowly than large-mass stars.mass stars.

Review continuedReview continued What is the difference between stars that What is the difference between stars that

become white dwarfs and stars that become become white dwarfs and stars that become neutron stars?neutron stars?

Giant stars collapse into neutron stars. Smaller Giant stars collapse into neutron stars. Smaller stars form white dwarfs.stars form white dwarfs.

What evidence do astronomers use to detect What evidence do astronomers use to detect black holes?black holes?

Scientist detect black holes by observing Scientist detect black holes by observing radiation from hot gas near the black hole, and radiation from hot gas near the black hole, and by studying the effect of the black hole’s gravity by studying the effect of the black hole’s gravity on a nearby star.on a nearby star.

Section 4Section 4Star Systems and GalaxiesStar Systems and Galaxies

Star Systems and PlanetsStar Systems and Planets

Our solar system has only one star, the Our solar system has only one star, the sun.sun.

More than half of all stars are members of More than half of all stars are members of groups of two or more stars, called star groups of two or more stars, called star systems.systems.

Binary Stars: Star systems with two stars Binary Stars: Star systems with two stars are called double stars or binary stars.are called double stars or binary stars.

Eclipsing Binary: A System in which one Eclipsing Binary: A System in which one star blocks the light from another.star blocks the light from another.

ReviewReview What was the Big Bang?What was the Big Bang? A giant explosion in which all the matter in the universe began A giant explosion in which all the matter in the universe began

moving apart.moving apart.

Describe how the solar system formed.Describe how the solar system formed. The solar system formed out of a collapsing, spinning disk of gas The solar system formed out of a collapsing, spinning disk of gas

and dust. The center of the disk formed the sun. Matter toward the and dust. The center of the disk formed the sun. Matter toward the edge formed the planets, asteroids, and a cloud of ice and other edge formed the planets, asteroids, and a cloud of ice and other substances.substances.

What observations show that the universe is expanding?What observations show that the universe is expanding? The galaxies are all moving away from each other. The farther away The galaxies are all moving away from each other. The farther away

a galaxy is away from the Milky Way, the faster it moves away, a galaxy is away from the Milky Way, the faster it moves away, because there is more space.because there is more space.

GalaxiesGalaxies

3 Main Galaxies3 Main Galaxies: Spiral Galaxies, : Spiral Galaxies, Elliptical Galaxies Elliptical Galaxies

Irregular GalaxiesIrregular Galaxies

SpiralSpiral: A galaxy that has the shape of twin : A galaxy that has the shape of twin spirals. spirals.

EllipticalElliptical: Look like flatten balls.: Look like flatten balls.

IrregularIrregular: Do not have a regular shape.: Do not have a regular shape.

ReviewReview

What is a star system?What is a star system?

A star system is a group of two or more stars.A star system is a group of two or more stars.

Describe the 3 main types of galaxies.Describe the 3 main types of galaxies.

Spiral galaxies are shaped like twin spirals, with arms that Spiral galaxies are shaped like twin spirals, with arms that spiral out like pinwheels. Elliptical galaxies look like flattened spiral out like pinwheels. Elliptical galaxies look like flattened balls. Irregular galaxies do not have regular shapes.balls. Irregular galaxies do not have regular shapes.

Where is the sun in our galaxy?Where is the sun in our galaxy?

The sun is about 25,000 light-years away from the center of The sun is about 25,000 light-years away from the center of the galaxy, about 2/3 of the way out in one of the spiral arms.the galaxy, about 2/3 of the way out in one of the spiral arms.

Section 5Section 5History of the UniverseHistory of the Universe

The galaxies in the universe are like the raisins The galaxies in the universe are like the raisins in rising bread. The raisins move away from in rising bread. The raisins move away from each other as the bread rises.each other as the bread rises.

The universe is getting bigger all the time.The universe is getting bigger all the time.

Big Bang TheoryBig Bang Theory The initial explosion The initial explosion

that resulted in the that resulted in the formation and formation and expansion of the expansion of the universe.universe.

The universe was The universe was small, hot, and small, hot, and dense. It exploded dense. It exploded about 10 to 15 billion about 10 to 15 billion years ago to make years ago to make our universe.our universe.

Formation of the Solar SystemFormation of the Solar System

After the big bang, matter in the universe separated into After the big bang, matter in the universe separated into galaxies. Gas and dust spread throughout space in our galaxies. Gas and dust spread throughout space in our galaxy. About 5 billion years ago, a giant cloud of gas galaxy. About 5 billion years ago, a giant cloud of gas and dust, or nebula, collapsed to form the solar system.and dust, or nebula, collapsed to form the solar system.

Nebula shrank to form a disk = the sun was born.Nebula shrank to form a disk = the sun was born. The spheres closest to the sun lost most of their gases The spheres closest to the sun lost most of their gases

and became the inner planets.and became the inner planets. The spheres farthest from the sun became the gas The spheres farthest from the sun became the gas

giants or the outer planets.giants or the outer planets.