The Universe 1.1 Welcome Welcome to The Universe, an online Earth and Space science tutorial for students in the 8th grade.
1.2 Objectives By the end of this tutorial, you should be able to recognize that the universe contains many billions of galaxies and that each galaxy contains many billions of stars. You will learn about how scientists study the universe and what the current understanding is on the size of the universe.
1.3 What Do We Know About Stars? There are a few things that you need to remember before you begin this tutorial. The first is that stars are made mostly of the elements hydrogen and helium. As the star generates energy through fusion it creates other elements that can form planets, moons and more. Stars are held together by gravity. Stars depending on their size and temperature can become large supergiant stars to older dim red giants to young hot white stars. They form from nebulae that could have been caused by a massive star explosion. Some stars actually turn into black holes. Stars can support planets and other objects through its radiation of energy. This variation is measured by their luminosity or brightness. Stars are so much larger than planets that they form solar systems kept together by gravity. Our Earth, other planets, asteroids, comets, etc. orbit our Sun in a solar system. Our Sun is a typical star that provides life on Earth. Stars form the basis of our understanding of the universe outside of our planet.
1.4 Practice 1 Let s review what you know about stars. Match the descriptions on the right with the correct terms on the left, and then click Submit to check your answers. Feedback when correct: Excellent! You know that our Sun is a typical star, that stars are classified by their luminosity, size and temperature, that stars generate energy and light through fusion of hydrogen into helium and that stars contain solar systems that include planets, moons, asteroids, comets and other debris. Feedback when incorrect: Our Sun is a typical star. Stars are classified by their luminosity, size and temperature. Stars generate energy and light through fusion of hydrogen into helium. Remember also that stars contain solar systems that include planets, moons, asteroids, comets and other debris. Drag Item Is a typical star Classified by luminosity, size and temperature How stars generate energy and light Mainly hydrogen and helium Drop Target Our Sun Stars Fusion What stars are made of
Drag Item Planets, moons, asteroids, comets, etc. orbiting a star Drop Target Solar System
1.5 Galaxies Stars are not just randomly scattered through the universe; they are gathered into groups called galaxies. Galaxies are made of gas, dust, stars, and the stars solar systems which include planets, moons, comets, asteroids and other debris. Each galaxy contains billions and billions of stars! They are huge. Galaxies are classified or organized into three main types and shapes, which are elliptical, spiral, and irregular. These main shapes are determined by the bulge at the center and the outer disk formations.
1.6 Practice 2 Let s practice. Select ALL the correct choices below that exist in any galaxy. Click submit to check your answers. Feedback when correct: Great! You know that gas, dust, as well as million and millions of stars with their solar system objects such as planets, their moons and asteroids and comets exist as parts of a galaxy. Feedback when incorrect: Actually all of these are correct. Gas, dust, as well as million and millions of stars with their solar system objects such as planets, their moons and asteroids and comets exist as parts of a galaxy. Correct Yes Yes Yes Yes Yes Choice Planets and their moons Gas Many millions of stars Dust Asteroids and comets
1.7 How Many Stars Are In The Milky Way? Let us look at our own galaxy, the Milky Way. On a dark, cloudless night if you go out and look up you may be able to see the faint haze that spreads across the sky. This is the Milky Way. The haze that you see is part of the spiral arm of the galaxy where the concentration of stars, gas, and dust makes it visible. Depending on where you are you might even see the bulge indicating the center of the galaxy. When you see the stars in the sky you are only seeing a small selection of stars that actually exist in our galaxy. Current estimates of star population within the Milky Way is around 300 billion stars. Scientists make a comparison between trying to count the number of stars in our galaxy to trying to count the number of grains of sand on one of Earth s beaches. We could never begin to count every grain of sand on a beach just like we could never imagine counting all the stars in our galaxy. So scientists make calculations about the number of stars in the Milky Way galaxy and others by estimating the number of stars in certain patches of the sky and multiplying these estimations.
1.8 Our Place In The Milky Way Where is our place in the Milky Way galaxy? Just like looking at a map if you are going on a trip, we can do the same thing to find our location in the galaxy. The Milky Way spiral galaxy has pinwheel type arms that our solar system happens to be part of. If you look on this map you can see the marked location of our Sun and where we are relative to the center of the galaxy. It is one quintillion kilometers from one side of our galaxy to the other. If you could travel as fast as the speed of light it would take you about 100,000 years to travel across the Milky Way. That s huge and it s only one galaxy! One of many millions out there! Didn t we already mention that the universe is HUGE?
1.9 Practice 3 Choose the best answer choice to describe the Milky Way. Correct Choice Feedback Yes The name of the galaxy in which our solar system is a part. Way to go. The Milky Way is the name of the spiral galaxy in which our solar system is a part. No The name of the next closest star. The next closest star to our Sun is within the star group Alpha Centauri. Try again to determine the best description of the Milky Way. No The name of our solar system. Our solar system is made up of the Sun and the objects like moons and planets that orbit it. Try again to determine the best description of the Milky Way. No The name of the observable universe. The observable universe is made up of other galaxies including the Milky Way. Try again to determine what the best description of the Milky Way is.
1.10 How Do We Learn About The Universe? - 1 How do we know all that we do about our universe? In the simplest of answers, we observe it! Humans have always looked to the sky with wonder and awe, but only so much of our universe can be seen with the unaided eye. Through the use and development of telescopes, scientists have made the most amazing observations about the universe. Telescopes come in all shapes and sizes from the typical ones you are used to seeing in backyards, local planetariums, or large array telescopes that take up acres of land, to telescopes that we place into space. Telescopes use light, but so much more than that. Telescopes measure different wavelengths of light and then use the wavelengths of the light to measure movement and distances. Modern telescopes interface with computers to aid in the calculations and modeling of systems. One of the most famous telescopes that has been orbiting the Earth since the 1990 s was launched by NASA and is named the Hubble Space Telescope after the astronomer, Edwin Hubble. The Hubble Space Telescope is as big as an oversized school bus and as it orbits the Earth it faces out toward space capturing pictures of galaxies, dying stars, star births, planets, moons and many more objects and events in space. These are just a small sampling of the images that the Hubble has provided and images like these and others allow us to gain immense knowledge about the universe we are part of. It is amazing to think about what we learn when we make observations about our universe.
1.11 How Do We Learn About The Universe? - 2 There are so many other missions that scientists have launched to study the known universe. There are probes that study black holes, gravity, radiation, interstellar medium, nebulae, supernovae, planets beyond the solar system, dark matter and more. All of these take observations and create models that can help us make sense of as we attempt to understand our complex universe. Astronomy is an amazing field but one of the few where we can t get close to the objects we are studying. We make observations with our instruments, make calculations, formulate hypotheses, test them, and run further tests as we explore. Our understanding of the cosmos has changed a lot in the last 25 years due to our increase in technology and our continuous search for answers to our questions.
1.12 Practice 4 How do we learn about the universe? Type your answer in the box. Feedback: Thank you for submitting your answer! Your response is unique, but take a few moments to compare your answer to this sample response. We use telescopes and probes to study the universe. We make observations on what we see, we run experiments, we collect and analyze data and update our theories as we seek to answer new questions. Did you include any of the same information in your answer? If so, great job!
1.13 How Many Galaxies Are In The Universe? If you went outside and held up a dime to the sky in an area where no stars were visible, how many stars do you think would be blocked by the coin? Most people didn t think they would see much. An astronomer Bob Williams, working with the Hubble telescope wanted to know. His team set the telescope to aim at a dark spot in the sky and take a long exposure picture. This is the result. This image is known as the Hubble Ultra Deep Field. Astronomers were extremely surprised by what they found. At first glance, you might think the image on the screen is just a cool picture of stars in the sky. However, each one of the objects in the picture is actually a galaxy and not just a single star! This small area contains an estimated 10,000 galaxies. With this one image it helped us understand a bit more about the size and age of the universe! If this one picture taken from the sky the size of a dime has 10,000 galaxies, how many galaxies are there in the entire universe? Based on current estimates there are at least 100 billion galaxies in the observable universe! Some estimates place the number closer to 225 billion galaxies. The information that is gathered about the vast nature of the universe increases every day. Let s take a short trip into the Hubble Ultra Deep Field.
1.14 How Many Stars Are In The Universe? So if the Milky Way galaxy is estimated at having 100 billion stars then how many stars are there in the entire universe? With an estimation of over 100 billion galaxies in the universe, and with galaxies containing upwards of hundreds of millions of stars each, it is amazing to think about how many stars exist in the universe. Current estimates of the star count put the number at approximately 1 x 10 24 stars which we can read as one septillion, or 1 with 24 zeros! To give you an idea of the size of that number let s consider how long it would take you to count that many stars. If you counted every star in the universe and each star took you 1 second to count, you would be counting the stars for almost 3.17 x 10 16 or 32 quadrillion years. That is a long, long time!
1.15 Practice 5 Let s practice again. Order the items based on the number of stars they possess starting from the largest number to fewest number of stars. Feedback when correct: What a star! The universe has an immense number of galaxies. Galaxies contain a large number of stars. The local star group may contain 10 to 1,000 stars within the galaxy and our solar system contains one star, the Sun. Feedback when incorrect: Let s review. The universe has an immense number of galaxies. Galaxies contain a large number of stars. The local star group may contain 10 to 1,000 stars within the galaxy and our solar system contains one star, the Sun. Drag Item Universe Galaxy Local Star Group Solar System Drop Target Largest 2 nd Largest 2 nd Smallest Smallest
1.16 Time or Distance? When we describe objects in the universe we use distances such as the light year or even parsecs. We know that light here on earth seems instantaneous. When you turn on a light switch the light comes on. When you see lightning, you hear the sound the lightning makes or thunder later. You have learned that sound is much slower than the light in lightning. But when we are talking about space, light actually helps us to calculate distances. Because the distances we are talking about are so great, it takes light time to get here in a way we can calculate and understand. The light from the sun takes 8 minutes to get here. So basically you are looking at the sun from 8 minutes ago. A light year is the distance light travels in one year. That is pretty far! Actually it equates to about 9.461 x 10 12 km! But when we are talking about objects in space, a light year covers a lot of ground. Our nearest star besides the sun, Proxima Centauri, is 4 light years away. It would take the light 4 years to get here after the photon left the star. Some of the stars you are looking at in the sky take more than a million light years to get here. That tells you they are pretty far, but actually we can only see so far with our eyes. Telescopes like the Hubble and others allow us to look even further. They are attempting to look to the edge of the universe. When we look far into space with these telescopes we are also looking back in time. Remember we said it takes light time to get here? Well, since it took so long for the light to get here, when we finally see it, it is light from the past. What that means is that the farther back you look the farther back in time you are looking. So when you look at the sky at night and peer at the stars, you are looking backwards in time! Wow!
1.17 The Observable Universe Scientists have estimated the size of the observable universe to be 93 billion light years across! Wow that is huge! It is even hard to comprehend! When we say observable that is because that is the farthest that we can see out with our current technology. If you looked out into the distance on land, your eyes can only see so far. This is the same with telescopes. The actual size of the universe might be larger or not, it all depends on the latest calculations and models put together with telescopes. Look to the center of this picture and you can see an area marked as the Virgo Supercluster. This is an area containing our galaxy. But it also contains other galaxies too. Remember again about how many stars are in each galaxy? So even in that tiny dot there are hundreds of billions of stars! Is this helping you to understand how huge the universe is yet?
1.18 Final Practice What does our universe contain? Read the choices and select all correct answers. Feedback when correct: Nice work! The universe is made up of hundreds of millions of galaxies that may be about 93 billion light years across. The universe contains all matter and energy that exists, and that looking out through the universe is like looking back in time! Feedback when incorrect: The universe is made up of hundreds of millions of galaxies that may be about 93 billion light years across. The universe contains all matter and energy that exists, and that looking out through the universe is like looking back in time! Correct Yes Yes Yes Yes Choice Made up of hundred of millions of galaxies Contains all of matter and energy that exists Currently it is estimated to be about 93 billion light years across Looking further into the universe is like looking back in time
1.19 Lesson Review The universe is an amazing place full of all matter and energy. There is still so much more to learn about! The universe contains galaxies made of stars and their solar systems, gas, dust and all matter. Our home galaxy is the Milky Way, which is an active spiral galaxy containing millions and millions of stars. We use telescopes both on our planet and in space to observe the universe around us. We send probes in space to study the universe. Within the universe scientists estimate large numbers of galaxies somewhere between 100 billion and 225 billion galaxies. If you added up all the stars in the universe we would find a number close to 1 septillion stars! The universe is so vast, that when we look into space we are actually looking back in time since it takes light so long to get here! The observable universe is more than 93 billion light years across. The universe is huge! Go outside tonight and look at the sky. What do you see?
1.20 Thank You Thank you for using this original tutorial. Be sure to check out our other original tutorials too. --------------------------------- Credits All images licensed from Getty Images, istock.com and/or Thinkstock.com, unless otherwise noted. The mysteries of UGC 8201. Hubble Space Telescope - https://www.spacetelescope.org/images/potw1510a/ Gas image. Hubble Gallery - http://hubblesite.org/newscenter/archive/releases/1992/29/image/a/ Stars image - Hubble Gallery - http://hubblesite.org/gallery/album/pr2006017c/ Mystery Mountain. Hubble Gallery - http://hubblesite.org/image/2707/news_release/2010-13 Giant Sun. By NASA/SDO/AIA/Goddard Space Flight Center - http://www.nasa.gov/mission_pages/rbsp/news/third-belt.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=24922453 Elliptical. NASA Gallery - http://www.spacetelescope.org/images/potw1515a/ Irregular Galaxy. NASA Gallery - http://hubblesite.org/newscenter/archive/releases/2005/09/image/a/ Spiral Galaxy. NASA Gallery - http://www.nasa.gov/images/content/611262main_hubble_holidaywreath1200_946-710.jpg Barred spiral galaxy: https://photojournal.jpl.nasa.gov/jpeg/pia07901.jpg Galaxy. Hubble Gallery - http://hubblesite.org/newscenter/archive/releases/2013/06/image/a/
Milky way map. NASA Gallery - http://www.nasa.gov/images/content/236084main_milkywayfull-annotated.jpg Milky way- NASA Gallery - http://apod.nasa.gov/apod/image/0508/mwart_spitzer_c42.jpg VLA Telescope. By CGP Grey - Flickr 2009-08-24T14-26-03 -- DSC_0065 4893503088, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=37019609 Hubble telescope - http://www.nasa.gov/sites/default/files/thumbnails/image/edu_what_is_hubble1.jpg Pink Nebula - http://hubblesite.org/gallery/album/pr2006001a Spiral - http://hubblesite.org/newscenter/archive/releases/2005/12/image/a/ Star cluster - http://hubblesite.org/gallery/album/pr2008031a Saturn - http://hubblesite.org/gallery/album/pr2003023b Comet - http://hubblesite.org/gallery/album/pr2013031a Orion nebula - http://hubblesite.org/gallery/album/pr1996007b Camera shutter sound, by semccab, http://freesound.org/people/semccab/sounds/154379/ Camera zoom sound, by sheepfilms, http://freesound.org/people/sheepfilms/sounds/154795/ Chandra telescope: https://www.nasa.gov/mission_pages/chandra/images/astronomerspursue-renegade-supermassive-black-hole.html Gravity Probe B: https://www.nasa.gov/mission_pages/gpb/gpb_012.html Kepler Space telescope: https://www.nasa.gov/sites/default/files/thumbnails/image/shareable_-_kepler_- _numbers_12may2015-2_1041sq.jpeg
Dawn spacecraft: https://www.jpl.nasa.gov/news/news.php?feature=3499 Crab Nubela: By NASA, ESA, G. Dubner (IAFE, CONICET-University of Buenos Aires) et al.; A. Loll et al.; T. Temim et al.; F. Seward et al.; VLA/NRAO/AUI/NSF; Chandra/CXC; Spitzer/JPL-Caltech; XMM-Newton/ESA; and Hubble/STScI - https://photojournal.jpl.nasa.gov/figures/pia21474_fig1.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=58809571 Small galaxy - http://hubblesite.org/newscenter/archive/releases/2004/2004/35/image/a/ Butterfly galaxy - http://hubblesite.org/newscenter/archive/releases/2009/25/image/f/ Nebula - http://hubblesite.org/gallery/album/pr2010013a Dr. Robert Williams. By STScIpubl - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=55281068 Deep Field - http://hubblesite.org/gallery/album/the_universe/hubble_ultra_deep_field/pr2014027a/ Deep Field Video - http://hubblesite.org/newscenter/archive/releases/2012/37/video/d/ Tick Tock sound, by FoolBoyMedia, http://freesound.org/people/foolboymedia/sounds/264498/ Phantom from Space. By Kevin MacLeod (incompetech.com), Licensed under Creative Commons: By Attribution 3.0 License, https://incompetech.com/music/royalty-free/music.html Universe. By 8_Observable_Universe_(ELitU).png: Azcolvin429derivative work: Frédéric MICHEL - 8_Observable_Universe_(ELitU).png, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16724575 Thunder and Rain sound, by FlatHill, http://freesound.org/people/flathill/sounds/237729/ Three-dimensional observable universe. By Andrew Z. Colvin - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=13251597
Sun s neighbors. By NASA/Penn State University - http://photojournal.jpl.nasa.gov/catalog/pia18003 (image link), Public Domain, https://commons.wikimedia.org/w/index.php?curid=32393431 Credits (Slide Layer)