AstronomyAstronomyStars, Galaxies, and the Stars, Galaxies, and the

UniverseUniverse

What is Astronomy?What is Astronomy?

Astronomy is the study Astronomy is the study of the moon, stars, and of the moon, stars, and other object in spaceother object in space

Astronomers study the Astronomers study the Universe using Universe using telescope, satellites, telescope, satellites, probes, as well as probes, as well as manned and manned and unmanned space unmanned space flightsflights

The UniverseThe Universe Astronomers define the Universe as all of space and Astronomers define the Universe as all of space and

everything in iteverything in it What’s found in the UniverseWhat’s found in the Universe

GalaxiesGalaxies NebulasNebulas StarsStars Solar Systems (planets, dwarf planets, moons)Solar Systems (planets, dwarf planets, moons) Asteroids, comets, meteors, meteoroidsAsteroids, comets, meteors, meteoroids Dark matter Dark matter

Does not give off electromagnetic energy and can not be Does not give off electromagnetic energy and can not be seen directlyseen directly

Estimated to make up 23% of the Universe’s mass Estimated to make up 23% of the Universe’s mass

The Origin of the UniverseThe Origin of the Universe

Astronomers believe that Astronomers believe that billions of years ago all billions of years ago all the matter and energy in the matter and energy in the Universe was the Universe was concentrated into single concentrated into single hot dense point called a hot dense point called a singularity singularity

Tremendous amounts of Tremendous amounts of heat and pressure made heat and pressure made this point so unstable that this point so unstable that it explodedit exploded

The Big Bang TheoryThe Big Bang TheoryAccording to the According to the Big Bang TheoryBig Bang Theory , the , the

Universe began to expand after an Universe began to expand after an enormous explosion of concentrated enormous explosion of concentrated matter and energymatter and energyAs it expanded, the Universe cooled As it expanded, the Universe cooled Atoms formed after a few hundred million Atoms formed after a few hundred million

yearsyearsThe first stars and galaxies formed after about The first stars and galaxies formed after about

200 million years200 million years

In Support of the Big BangIn Support of the Big Bang Moving Galaxies-Moving Galaxies-

Edwin Hubble discovered that almost all galaxies are moving away from us and from each other

Hubble’s Law- the farther away a galaxy is, the faster it is moving away from us

Cosmic Background Radiation-Cosmic Background Radiation- The electromagnetic radiation (thermal energy)

leftover from the big bang Detected with a radio telescope in 1965 by Arno

Penzias and Robert Wilson

Age of the UniverseAge of the Universe

Can be determined based on Can be determined based on measurements of how fast distant galaxies measurements of how fast distant galaxies are moving away from us as and from the are moving away from us as and from the cosmic background radiationcosmic background radiation

Astronomers estimateAstronomers estimate

that the Universe is that the Universe is

13.7 billion years old13.7 billion years old

Future of the UniverseFuture of the Universe

Background radiation, left over from the Background radiation, left over from the Big Bang, has led astronomers to two Big Bang, has led astronomers to two possible fates for the Universe possible fates for the Universe

Closed Universe-Closed Universe- A universe that would A universe that would expand then collapse back in on itselfexpand then collapse back in on itself

Open Universe-Open Universe- A universe that would A universe that would continue to expandcontinue to expand

A Closed UniverseA Closed Universe

A possible future for the Universe in which the A possible future for the Universe in which the force of gravity would pull the galaxies back force of gravity would pull the galaxies back together together

Would result in a “reverse big bang” or a “big Would result in a “reverse big bang” or a “big crunch”crunch”

After many billions of years, all the matter and After many billions of years, all the matter and energy in the Universe would be concentrated energy in the Universe would be concentrated in an enormous black holein an enormous black hole

The final result could be another “Big Bang” The final result could be another “Big Bang” billions of years from nowbillions of years from now

An Open UniverseAn Open Universe A possible future where the galaxies continue A possible future where the galaxies continue

racing outward, expanding the Universe racing outward, expanding the Universe Stars would eventually run out of fuel and Stars would eventually run out of fuel and

burn out, leaving the Universe cold and darkburn out, leaving the Universe cold and dark New evidence leads astronomers to believe New evidence leads astronomers to believe

that dark energy is causing the expansion of that dark energy is causing the expansion of the Universe to accelerate and that it will the Universe to accelerate and that it will likely expand foreverlikely expand forever

Galaxies Galaxies

A galaxy is a large A galaxy is a large system of stars and system of stars and other cosmic bodiesother cosmic bodies

Galaxies are the major Galaxies are the major features of the Universefeatures of the Universe

There may be more There may be more than 100 billion major than 100 billion major galaxies galaxies

There are three main There are three main types of galaxiestypes of galaxies

Spiral GalaxiesSpiral Galaxies

Have a bulge in the middle and arms that Have a bulge in the middle and arms that spiral outward, like pinwheelsspiral outward, like pinwheels

Bright, central nucleus is made up of Bright, central nucleus is made up of millions of starsmillions of stars

Spiral arms contain millions of bright, Spiral arms contain millions of bright, young stars as well as dust and gasyoung stars as well as dust and gas

Example: our Milky Way GalaxyExample: our Milky Way Galaxy

The Milky Way Galaxy is approximately 100,000 light years across. We are located about 25,000 light years from the center, out on one of the spiral arms

Elliptical GalaxiesElliptical Galaxies

Vary in shape from nearly spherical to Vary in shape from nearly spherical to flattened disksflattened disks

Most of the stars are close to the centerMost of the stars are close to the center Have no armsHave no arms Contains billions of stars but little gas or Contains billions of stars but little gas or

dustdust Stars are no longer forming and are Stars are no longer forming and are

generally older than those in the other generally older than those in the other galaxiesgalaxies

Irregular GalaxiesIrregular Galaxies

Have no definite shapeHave no definite shape Stars are spread unevenlyStars are spread unevenly Typically smaller than other Typically smaller than other

types of galaxiestypes of galaxies Generally have many bright Generally have many bright

young stars and lots of gas and young stars and lots of gas and dust to form new starsdust to form new stars

Quasars (quasi-stellar objects)Quasars (quasi-stellar objects)

Very bright, distant Very bright, distant objectsobjects Many 10 billion light Many 10 billion light

years awayyears away Look almost like starsLook almost like stars

Believed to be active Believed to be active young galaxies with young galaxies with enormous amounts of enormous amounts of gas revolving around a gas revolving around a giant black in their giant black in their centerscenters

StarsStars There may be as many as 200 quintillion stars in There may be as many as 200 quintillion stars in

the universe (200,000,000,000,000,000,000)the universe (200,000,000,000,000,000,000) Stars are huge spheres of glowing gasStars are huge spheres of glowing gas

Made up mostly of hydrogenMade up mostly of hydrogen Produce energy by nuclear fusionProduce energy by nuclear fusion

Stars differ in size,Stars differ in size,

mass, color, compositionmass, color, composition

temperature, and temperature, and

brightnessbrightness

Color & Temperature of StarsColor & Temperature of StarsThe color of stars can be used to determineThe color of stars can be used to determine

their surface temperaturetheir surface temperature

BlueBlue = 35,000 = 35,000°C°CWhite = 10,000°CWhite = 10,000°CYellowYellow = 6,000°C = 6,000°CRed-orangeRed-orange = 5,000°C = 5,000°CRedRed = 3,000°C = 3,000°C

The temperature at the center of a star is much greater thanat its surface

Stars are divided into 5 main Stars are divided into 5 main groups according to sizegroups according to size

Neutron stars-Neutron stars- the smallest stars the smallest stars (avg. diameter = 16 km)(avg. diameter = 16 km)

White dwarfs-White dwarfs- smaller than the Earth smaller than the Earth (ex. Van Maanen’s star)(ex. Van Maanen’s star)

Medium-sized stars-Medium-sized stars- vary in size from vary in size from 1/10 to 10 times the size of the Sun 1/10 to 10 times the size of the Sun (ex. the Sun & Sirius)(ex. the Sun & Sirius)

Giant stars-Giant stars- 10 to 100 times as large as 10 to 100 times as large as the Sun (ex. Aldebara)the Sun (ex. Aldebara)

Supergiant stars-Supergiant stars- up to 1000 times larger up to 1000 times larger than the Sun (ex. Rigel & Betelgeuse)than the Sun (ex. Rigel & Betelgeuse)

Smallest

Largest

Composition of StarsComposition of Stars

Spectroscopes are used to determine the Spectroscopes are used to determine the composition of starscomposition of stars

Almost all stars have the same Almost all stars have the same compositioncomposition

60 - 80% hydrogen60 - 80% hydrogen20 – 30% helium20 – 30% helium2% other elements2% other elements

Brightness of StarsBrightness of Stars

The brightness of a star depends on its The brightness of a star depends on its size, its surface temperature, and its size, its surface temperature, and its distance from Earthdistance from Earth

Apparent magnitude-Apparent magnitude- the brightness of a the brightness of a star as it appears from Earthstar as it appears from Earth

Absolute magnitude-Absolute magnitude- the amount of light the amount of light a star actually gives offa star actually gives off

Hertzsprung-Russell DiagramHertzsprung-Russell Diagram

A chart that shows the relationship A chart that shows the relationship between the absolute magnitude and the between the absolute magnitude and the surface temperature of starssurface temperature of stars

Astronomers use H-R diagrams to classify Astronomers use H-R diagrams to classify stars and to understand how stars change stars and to understand how stars change over timeover time

As the absolute magnitude of main As the absolute magnitude of main sequence stars increases, the temperature sequence stars increases, the temperature increase as wellincrease as well

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Measuring Distances to StarsMeasuring Distances to Stars

Astronomers use light years to measure distances Astronomers use light years to measure distances between starsbetween stars A light year is the distance light travels in a year, 9.5 A light year is the distance light travels in a year, 9.5

trillion kilometerstrillion kilometers Parallax is used to measure distances to nearby Parallax is used to measure distances to nearby

stars stars Parallax is the apparent change inParallax is the apparent change in

position of an object when you look at position of an object when you look at

it from different placesit from different places The star is viewed when Earth is on The star is viewed when Earth is on

one side of the Sun and then six monthsone side of the Sun and then six months

later when Earth is on the other side of the Sun later when Earth is on the other side of the Sun

Evolution of StarsEvolution of Stars

Stars evolve, or change, over timeStars evolve, or change, over timeThe amount of mass a star begins with is The amount of mass a star begins with is

the main factor that determines its the main factor that determines its evolutionevolution

The different kinds of stars in the sky The different kinds of stars in the sky represent the various stages in the life represent the various stages in the life cycle of stars cycle of stars

Stages in the Life Cycle of Stars Stages in the Life Cycle of Stars All stars are created from the gases in a nebulaAll stars are created from the gases in a nebula When the contracting gas and dust from a nebula When the contracting gas and dust from a nebula

become so dense and hot that become so dense and hot that nuclear fusion begins, nuclear fusion begins, the the protostarprotostar begins to shine begins to shine

When a star begins to run out of fuel, its core shrinks When a star begins to run out of fuel, its core shrinks and its outer portion expands and its outer portion expands

The evolutionary path of a star depends on its massThe evolutionary path of a star depends on its mass Medium-sized starsMedium-sized stars Expand to Expand to red giantsred giants white dwarfswhite dwarfs

dims to a dims to a black dwarfblack dwarf or or dead stardead star Massive starsMassive stars Expand to Expand to red giantsred giants or or supergiantssupergiants

explode in a explode in a supernovasupernova become a become a neutron starneutron star or a or a black black hole hole (depending on initial mass) (depending on initial mass)

Possible Evolutionary Paths for StarsPossible Evolutionary Paths for Stars

ConstellationsConstellations

Groups of stars that form a patternGroups of stars that form a pattern The revolution of the Earth around the Sun The revolution of the Earth around the Sun

cause different constellations to be seen at cause different constellations to be seen at different times of the yeardifferent times of the year

Stars located above the north and south poles, Stars located above the north and south poles, called called circumpolar starscircumpolar stars, appear to move in , appear to move in circles above the horizon each night circles above the horizon each night

Astronomers use constellations as landmarks to Astronomers use constellations as landmarks to locate other objects in the skylocate other objects in the sky

Constellations in the AutumnConstellations in the Autumn SkySky

Optical TelescopesOptical Telescopes

Tools that use large lenses or mirrors to gather Tools that use large lenses or mirrors to gather rays of light from a star and focus it in one spotrays of light from a star and focus it in one spot

The light-gathering power depends on the area The light-gathering power depends on the area of its lens or mirror (the greater the area, the of its lens or mirror (the greater the area, the more light it can gather)more light it can gather)

Have three basic functionsHave three basic functions1.1. Collect more light than the naked eyeCollect more light than the naked eye

2.2. Separate distant objects from one anotherSeparate distant objects from one another

3.3. Magnify imagesMagnify images

Refracting TelescopesRefracting Telescopes

Use convex lenses to gather light Use convex lenses to gather light The lensesThe lenses

refractrefract (bend) (bend)

the rays of the rays of

light to formlight to form

an imagean image

Reflecting TelescopesReflecting Telescopes Use mirrors to gather and focus lightUse mirrors to gather and focus light

Types of Optical TelescopesTypes of Optical Telescopes

How Light BehavesHow Light Behaves

Light travels in straight-line paths called raysLight travels in straight-line paths called rays

Reflection- Reflection- When light strikesWhen light strikes

a surface, some of it bounces a surface, some of it bounces

backback

Refraction-Refraction- The bending of The bending of

light due to a change in speedlight due to a change in speed

Mirrors Reflect LightMirrors Reflect Light Mirrors are classified based on the shape of Mirrors are classified based on the shape of

their surfacetheir surface Plane mirrors-Plane mirrors-

Perfectly flat surfacesPerfectly flat surfaces Image appears to be on the other side of the mirrorImage appears to be on the other side of the mirror

Concave mirrors-Concave mirrors- Surface curves inwardSurface curves inward Reflect light rays to the same point in front of the mirror Reflect light rays to the same point in front of the mirror

(focal point)(focal point) Convex mirrors-Convex mirrors-

Surface curves outwardSurface curves outward Reflected rays spread out from the surface of the mirrorReflected rays spread out from the surface of the mirror

Types of MirrorsTypes of Mirrors

Lenses Refract LightLenses Refract Light Convex lenses-Convex lenses- Lenses that are thicker in the Lenses that are thicker in the

center than at the edgescenter than at the edges Bend rays of light toward the thicker centerBend rays of light toward the thicker center of the lensof the lens The amount of refraction depends on how The amount of refraction depends on how much the lens curves (the greater the curve,much the lens curves (the greater the curve, the more the light is refracted)the more the light is refracted) Converge light rays at the focal pointConverge light rays at the focal point

Concave Lenses-Concave Lenses- Lenses that are thinner in the Lenses that are thinner in the center than at the edgescenter than at the edges

Bend rays of light outward toward the Bend rays of light outward toward the thicker ends of the lensthicker ends of the lens Diverge rays of lightDiverge rays of light

Types of LensesTypes of Lenses