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