Physical Geography - Version 1 Unit 2 Earth’s Place within the Cosmos

Figure The Milky Galaxy . Image by NASA is in the public domain . UNIT EARTH PLACE WITHIN THE COSMOS Goals Objectives of this unit Understand the scientific ideas of how the universe formed and is expanding . Compare and contrast the difference and similarities between dark matter and dark energy . Describe star systems and the various types of galaxies . Explain the phenomenal power within stars . Classifying and measuring distant stars . GEOGRAPHY

INTRODUCTION TO THE UNIVERSE The Whirlpool Galaxy , also known as , is a spiral galaxy about 23 million from Earth . Its interactions with the yellowish dwarf galaxy 5195 are of interest to astronomers because the galaxies are near enough to Earth to be . Decades ago , astronomers could not tell if these two galaxies were just passing each other but radio astronomy has supplied astronomers with important data outlining their interactions . Using this data , astronomers have simulated the interaction . 5195 came from behind and then passed through the main disk of about 500 to 600 million years ago . The dwarf galaxy crossed the disk again between 50 and 100 million years ago and is now slightly behind . These interactions appear to have intensified the spiral arms that are the dominant characteristic of the Whirlpool Galaxy . Astronomers can learn about objects unimaginably far away from Earth using telescopes that sense all wavelengths on the electromagnetic spectrum . Imagine what Galileo would do if he could see the images and data astronomers have available to them now . The study of the universe is called cosmology . Cosmologists study the structure and changes in the present universe . The universe contains all of the star systems , galaxies , gas , and dust , plus all the matter and energy that exists now , that existed in the past , and that will exist in the future . The universe includes all of space and time . EXPANDING UNIVERSE What did the ancient Greeks recognize as the universe ?

In their model , the universe contained Earth at the center , the Sun , the Moon , five planets , and a sphere to which all the stars were attached . This idea held for many centuries until Galileo telescope helped allow people to realize that Earth is not the center of the universe . They also found out that there are many more stars than were visible to the naked eye . All of those stars were in the Milky Way Galaxy . In the early 20 century , an astronomer named Edwin Hubble discovered that what scientists called the Andromeda Nebula was over two million away , many times farther than the farthest distances that had ever been measured . Hubble realized that many of the objects that astronomers called nebulae were not clouds of gas but were collections of millions or billions of stars that we now call galaxies . Hubble showed that the universe was much larger than our galaxy . Today , we know that the universe contains about a hundred billion galaxies , about the same number of galaxies as there are stars in the Milky Way Galaxy . After discovering that there are galaxies beyond the Milky GEOGRAPHY

Way , Edwin Hubble went on to measure the distance to hundreds of other galaxies . His data would eventually show how the universe is changing and would even yield clues as to how the universe formed . Today we know that the universe is nearly 14 billion years old . If you look at a star through a prism , you will see a spectrum or a range of colors through the rainbow . The spectrum will have specific dark bands where elements in the star absorb light of certain energies . By examining the arrangement of these dark absorption lines , astronomers can determine the composition of elements that make up a distant star . The element helium was first discovered in our Sun , not on Earth , by analyzing the absorption lines in the spectrum of the Sun . While studying the spectrum of light from distant galaxies , astronomers noticed something strange . The dark lines in the spectrum were in the patterns they expected , but they were shifted toward the red end of the spectrum , as shown in Figure below . This shift of absorption bands toward the red end of the spectrum is known as . occurs when the light source is moving away from the observer or when the space between the observer and the source is stretched . What does it mean that stars and galaxies are ?

When astronomers see in the light from a galaxy , they know that the galaxy is moving away from Earth . What astronomers are noticing is that all the galaxies have a , strongly indicating that all galaxies are moving away from each other causing the Universe to expand . can occur with other types of waves too , called the Doppler Effect . An analogy to is the noise a siren makes as it passes you . You may have noticed that an ambulance seems to lower the pitch of its siren after it passes you . The sound waves shift towards a lower pitch when the ambulance speeds away from you . Though involves light instead of sound , a similar principle operates in both situations . Figure Diagram . As a Particle Moves , the Wave Frequencies Increase . Image NASA is in the public domain . GEOGRAPHY

The Expanding Universe Edwin Hubble combined his measurements of the distances to galaxies with other astronomers measurements of . From this data , he noticed a relationship , which is now called Law . The law states that the farther away a galaxy is , the faster it is moving away from us . What this leads to is the hypothesis that the universe is expanding . The figure below by NASA shows a simplified diagram of the expansion of the universe . lfyou look closely at the diagram , it is observed that on the left was the formation of the universe , and the energy is quite high . Over the course of the billion years , the energy begins to cool enough to create trillions of stars and over time develop into galaxies . Over time , the galaxies continue to cool and expand farther apart from each other . Figure Shows Slices of Expansion of Universe Without an Initial Singularity . Image by NASA is in the public domain . FORMATION OF THE UNIVERSE Before Hubble , most astronomers thought that the universe did change . But ifthe universe is expanding , what does that say about where it was in the past ?

universe is expanding , the next logical thought is that in the past it had to have been smaller . The Big Bang Theory Big Bang Theory is the most widely accepted cosmological explanation of how the universe formed . If we start at the present and go back into the past , the universe is contracting , getting smaller and smaller . What is the result of a contracting universe ?

According to the Big Bang theory , the universe began about billion years ago . Everything that is now in the universe was squeezed into a very small volume . Imagine all of the known universes in a single , hot , chaotic mass . An enormous explosion , a big bang , caused the universe to start expanding rapidly . All the matter and energy in the universe , and even space itself , came out of this GEOGRAPHY

explosion . What came before the Big Bang ?

There is no way for scientists to know since there is no remaining evidence . Dark Energy Accelerated Expansion Afterglow Light Pattern Dark Ages Development of yrs . Galaxies , Planets , etc . Inflation about 400 million yrs . Big Bang Expansion billion years Figure The Big Bang Theory , Measuring the Expansion Over a Period Years . Image by NASA is in the public domain . After the Big Bang In the first few moments after the Big Bang , the universe was unimaginably hot and dense . As the universe expanded , it became less dense and began to cool . After only a few seconds , protons , neutrons , and electrons could form . After a few minutes , those subatomic particles came together to create hydrogen . The energy in the universe was great enough to initiate nuclear fusion and hydrogen nuclei were fused into helium nuclei . The first neutral atoms that included electrons did not form until about years later . The matter in the early universe was not smoothly distributed across space . Dense clumps of matter held close together by gravity were spread around . Eventually , these clumps formed countless trillions of stars , billions of galaxies , and other structures that now form most of the visible mass of the universe . If you look at an image of galaxies at the far edge of what we can see , you are looking at great distances . But you are also looking across a different type of distance . What do those far away galaxies represent ?

Because it takes so long for light from so far away to reach us , you are also looking back in time . GEOGRAPHY Dark Matter The Big Bang Theory is still the best scientific model we have for explaining the formation of the universe and many lines of evidence support it . However , recent discoveries continue to shake up our understanding ofthe universe . Astronomers and other scientists are now wrestling with some unanswered questions about what the universe is made of and why it is expanding . A lot of what cosmologists do is create mathematical models and computer simulations to account for these unknown phenomena , such as dark energy and dark matter . Scientists are much more certain what dark matter is not than we are what it is . First , it is dark , meaning that it is not in the form of stars and planets that we see . Observations show that there is far too little visible matter in the universe to make up the 27 required by the observations . Second , it is not in the form of dark clouds of normal matter , matter made up of particles called . We know this because we would be able to detect clouds by their absorption of radiation passing through them . Third , dark matter is not antimatter , because we do not see the unique gamma rays that are produced when antimatter annihilates with matter . Finally , we can rule out large black holes based on how many gravitational lenses we see . High concentrations of matter bend light passing near them from objects further away , but we do not see enough lensing events to suggest that such objects make up the required 25 dark matter contribution . Dark Energy Astronomers who study the expansion of the universe are interested in knowing the rate of that expansion . Is the rate fast enough to overcome the attractive pull of gravity ?

If yes , then the universe will expand forever , although the expansion will slow down over time . If no , then the universe would someday start to contract , and eventually get squeezed together in a big crunch , the opposite ofthe Big Bang . Recently astronomers have made a discovery that answers that question the rate at which the universe is expanding is increasing . In other words , the universe is expanding faster now than ever before , and in the future , it will expand even faster . So now astronomers think that the universe will keep expanding forever . But it also proposes a perplexing new question What is causing the expansion of the universe to accelerate ?

One possible hypothesis involves a new , hypothetical form of energy called dark energy . Some scientists think that dark energy makes up as much as 72 of the total energy content of the universe . GEOGRAPHY STAR SYSTEMS GALAXIES Although constellations have stars that usually only appear to be close together , stars may be found in the same portion of space . Stars that are grouped closely together are called star systems . Larger groups of hundreds or thousands of stars are called star clusters . The image shown here is a famous star cluster classed , also known as , which can be seen with the naked autumn sky . Although the star humans know best is a single star , many stars , more than half of the bright stars in our galaxy are star systems . A system of two stars orbiting each other is a binary star . A system with more than two stars orbiting each other is a multiple star system . The stars in a binary or multiple star system are often so close together that they appear as only through a telescope can the pair be distinguished . Figure 213 Star Cluster . Image by NASA is in the public domain . Star Systems Star clusters are divided into two main types , open clusters , and globular clusters . Open clusters are groups of up to a few thousand stars that are loosely held together by gravity . The is an open cluster that is also called the Seven Sisters . Open clusters tend to be blue and often contain glowing gas and dust . Open clusters are made of young stars that are formed from the same nebula . The stars may eventually be pulled apart by gravitational attraction to other objects . GEOGRAPHY

Globular Clusters Globular clusters are groups of tens to hundreds of thousands of stars held tightly together by gravity . Globular clusters have a definite , spherical shape and contain mostly reddish stars . The stars are closer together , closer to the center of the cluster . Globular clusters do have much dust in them , the dust has already formed into stars . Spiral Galaxies Galaxies are the biggest groups of stars and can contain anywhere from a few million stars to many billions of stars . Every star that is visible in the night sky is part of the Milky Way Galaxy . To the naked eye the closest major galaxy , the Andromeda Galaxy , looks like only a dim , fuzzy spot but that fuzzy spot contains one trillion stars . Spiral galaxies spin , so they appear as a rotating disk of stars and dust , with a bulge in the middle , like the Sombrero Galaxy . Several arms spiral outward in the Pinwheel Galaxy and are appropriately called spiral arms . Spiral galaxies have lots of gas and dust and lots of young stars . Other galaxies are and called an elliptical galaxy . The smallest elliptical galaxies are as small as some globular clusters . Giant elliptical galaxies , on the other hand , can contain over a trillion stars . Elliptical galaxies are reddish to yellowish because they contain mostly old stars . Most elliptical galaxies contain very little gas and dust because they had already formed . However , some elliptical galaxies contain lots of dust . Figure The Andromeda Galaxy . Image by NASA is in the public domain . GEOGRAPHY

Irregular Dwarf Galaxies Galaxies that are not elliptical galaxies or spiral galaxies are irregular galaxies . Most irregular galaxies were once spiral or elliptical galaxies that were then deformed either by gravitational attraction to a larger galaxy or by a collision with another galaxy . Dwarf galaxies are small galaxies containing only a few million to a few billion stars . Dwarf galaxies are the most common type in the universe . However , because they are relatively small and dim , we do see as many dwarf galaxies from Earth . Most dwarf galaxies are irregular in shape . However , there are also dwarf elliptical galaxies and dwarf spiral galaxies . Look back at the picture of the spiral galaxy , Andromeda . Next to our closest galaxy neighbor are two dwarf elliptical galaxies that are companions to the Andromeda Galaxy . One is a bright sphere to the left of the center , and the other is a long ellipse below and to the right of the center . Dwarf galaxies are often found near larger galaxies . They sometimes collide with and merge into their larger neighbors Figure An irregularly Shaped Galaxy . Image by NASA is in the public domain . GEOGRAPHY

THE MILKY WAY GALAXY On a dark , clear night , you can see a milky band of light stretching across the sky . This band is the disk of a galaxy , the Milky Way Galaxy is our galaxy and is made of millions of stars along with a lot of gas and dust . Although it is difficult to know what the shape of the Milky Way Galaxy is because we are inside of it , astronomers have identified it as a typical spiral galaxy containing about 100 billion to 400 billion stars . Figure Artist Conception of the Spiral Structure ofthe Milky Way . Image by NASA is in the public domain . Artist conception of the spiral structure of the Milky Way with two major stellar arms and a central bar . Using infrared images from NASA Space Telescope , scientists have discovered that the Milky Way elegant spiral structure is dominated two arms wrapping off the ends of a central bar of stars . Previously , our galaxy was thought to possess four major arms . GEOGRAPHY

Like other spiral galaxies , our galaxy has a disk , a central bulge , and spiral arms . The disk is about across and thick . Most of the Galaxy gas , dust , young stars , and open clusters are in the disk . What data and evidence do astronomers find that lets them know that the Milky Way is a spiral galaxy ?

The shape ofthe galaxy as we see it . The velocities of stars and gas in the galaxy show a rotational motion . The gases , color , and dust are typical of spiral galaxies . The central bulge is about to wide and to thick . The central bulge contains mostly older stars and globular clusters . Some recent evidence suggests the bulge might not be spherical but is instead shaped like a bar . The bar might be as long as long . The disk and bulge are surrounded by a faint , spherical halo , which also includes old stars and globular clusters . Astronomers have discovered that there is a gigantic black hole at the center of the galaxy . Figure Grid Added to Annotated Milky Way . Image by NASA is in the public domain . GEOGRAPHY

The Milky Way Galaxy is a significant place . Our solar system , including the Sun , Earth , and all the other planets , is within one of the spiral arms in the disk of the Milky Way Galaxy . Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm . Earth is about from the center of the galaxy , a little more than halfway out from the center of the galaxy to the edge . Just as Earth orbits the Sun , the Sun and solar system orbit the center of the Galaxy . One orbit of the solar system takes about 225 to 250 million years . The solar system has orbited 20 to 25 times since it formed billion years ago . Astronomers have recently found that at the center of the Milky Way , and most other galaxies , is a supermassive black hole , though a black hole can not be seen . STAR ENERGY NUCLEAR FUSION A solar flare , also known as a corona , is a long filament of solar material , erupting out from the sun into space . The Sun is Earth major source of energy , yet the planet only receives a small portion of its energy and the Sun is just an ordinary star . Many stars produce much more energy than the Sun . The energy source for all stars is nuclear fusion . Stars are made mostly of hydrogen and helium , which are packed so densely in a star that is the star center the pressure is great enough to initiate nuclear fusion reactions . In a nuclear fusion reaction , the nuclei of two atoms combine to create a new atom . Most commonly , in the core of a star , two hydrogen atoms fuse to become a helium atom . Figure 18 Solar Flare or Corona . Image by NASA is in the public domain . GEOGRAPHY

Although nuclear fusion reactions require a lot of energy to get started , once they are going , they produce enormous amounts of energy . In a star , the energy from fusion reactions in the core pushes outward to balance the inward pull of gravity . This energy moves outward through the layers of the star until it finally reaches the star outer surface . The outer layer of the star glows brightly , sending the energy out into space as electromagnetic radiation , including visible light , heat , ultraviolet light , and radio waves . In particle accelerators , subatomic particles are propelled until they have attained almost the same amount of energy as found in the core of a star . When these particles collide , new particles are created . This process stimulates the nuclear fusion that takes place in the cores of stars . The process also stimulates the conditions that allowed for the first helium atom to be produced from the collision of two hydrogen atoms in the first few minutes of the universe . STAR CLASSIFICATION Think about how the color of a piece of metal changes with temperature . A coil of an electric stove will start out black but with added heat will start to glow a dull red . With more heat , the coil turns a brighter red , then orange . At extremely high temperatures the coil will turn white , or even ( it hard to imagine the flame on your stove getting that hot ) A star color is also determined by the temperature of the star surface . Relatively cool stars are red , warmer stars are orange or yellow , and extremely hot stars are blue or . Color is the most common way to classify stars . The table below shows the classification system . The class of a star is given by a letter . Each letter corresponds to a color , and also to a range of temperatures . Note that these letters do match the color names they are leftover from an older system that is no longer used . For most stars , the surface temperature is also related to size . Bigger stars produce more energy , so their surfaces are hotter . These stars tend toward . Smaller stars produce less energy . Their surfaces are less hot and so they tend to be yellowish . GEOGRAPHY

i ' Mars ' mus Figure Relative Sizes Planets in the Solar System and Several Stars . Image by NASA is used under a Alike license . The Main Sequence For most of a star life , nuclear fusion in the core produces helium from hydrogen . A star in this stage is a star . This term comes from the diagram shown here . For stars in the main sequence , the temperature is directly related to brightness . A star is on the main sequence as long as it can balance the inward force of gravity with the outward force of nuclear fusion in its core . The more massive a star , the more it must burn hydrogen fuel to prevent gravitational collapse . Because they burn more fuel , more massive stars have higher temperatures . Massive stars also run out of hydrogen sooner than smaller stars do . Our Sun has been a star for about billion years and will continue on the main sequence for about billion more years . Very large stars may be in the main sequence for only 10 million years . Very small stars may last tens to hundreds of billions of years . GEOGRAPHY

Antares 9352 725 A Gliese 725 Star I Ross 1254 Wolf 359 ' Canon ' mew in a Figure Main Sequence ofa Stars Life . Image by NASA is in the public domain . Red Giants White Dwarfs As a star begins to use up its hydrogen , it fuses helium atoms together into heavier atoms such as carbon . A blue giant star has exhausted its hydrogen fuel and is a transitional phase . When the light elements are mostly used up the star can no longer resist gravity and it starts to collapse inward . The outer layers of the star grow outward and cool . The larger , cooler star turns red and so is called a red giant . Eventually , a red giant burns up all of the helium in its core . What happens next depends on how massive the star is . A typical star , such as the Sun , stops fusion completely . Gravitational collapse shrinks the star core to a white , glowing object about the size of Earth , called a white dwarf . A white dwarf will ultimately fade out . GEOGRAPHY

Supernovas A star that runs out of helium will end its life much more dramatically . When very massive stars leave the main sequence , they become red . Unlike a red giant , when all the helium in a red supergiant is gone , fusion continues . Lighter atoms fuse into heavier atoms up to iron atoms . Creating elements heavier than iron through fusion uses more energy than it produces so stars do not ordinarily form any heavier elements . When there are no more elements for the star to fuse , the core succumbs to gravity and collapses , creating a violent explosion called a supernova . A supernova explosion contains so much energy that atoms can fuse together to produce heavier elements such as gold , silver , and uranium . A supernova can shine as brightly as an entire galaxy for a short time . All elements with an atomic number greater than that of lithium were created by nuclear fusion in stars . Figure Image of the Crab Nebula . Image by NASA is in the public domain . Neutron Stars Black Holes After a supernova explosion , the leftover material in the core is extremely dense . If the core is less than about four times the mass of the Sun , the star becomes a neutron star . A neutron star is made almost entirely of neutrons , relatively large particles that have no electrical charge . If the core remaining after a supernova is more than about five times the mass of the Sun , the core collapses into a black hole . Black holes are so dense that not even light can escape their gravity . With no light , a black hole can not be observed directly . But a black hole can be identified by the effect that it has on objects around it , and by radiation that leaks out around its edges . GEOGRAPHY

Figure . 22 Simulated View Black Hole in Front of the Large Cloud . Image by NASA is in the public domain . SUMMARY Astronomy is one of the oldest sciences , and early civilizations performed methodical observations ofthe night sky , and astronomical artifacts have been found from much earlier periods . However , the invention ofthe telescope was required before astronomy was able to develop into a modern science . The Big Bang Theory is the most widely accepted cosmological explanation of how the universe formed . At its simplest , it says the universe as we know it started with a small singularity , then inflated over the next billion years to the cosmos that we know today Image result for milky way summary The Milky Way contains over 200 billion stars , and enough dust and gas to make billions more . The solar system lies about from the galactic center and about 20 above the plane of the galaxy . More than half the stars found in the Milky Way are older than the sun . GEOGRAPHY