Stars and Galaxies

Stars and Galaxies Chapter 25

Section 1 The Study of Stars • Objectives: • Describe the electromagnetic spectrum • Explain how reflecting and refracting telescopes work • Compare and Contrast optical telescopes and spectroscopes • Infer the relationship between the frequency of electromagnetic waves and their wavelength

Skills Warm-up • Star Words • Write as many words as you can to describe stars from just observing them. • Write something you know about stars but can’t tell by just looking at them. • Compare your words with your classmates.

Stars • Stars are swirling, glowing balls of gas • There are > 200,000,000,000 billion • The sun is very important to earth, but it is just an average star • Many other stars are much bigger and brighter • How are stars studied?

Electromagnetic Spectrum • All stars produce energy in the form of electromagnetic waves: • Visible light • Radio waves • Heat • X-rays • Each type of energy has a characteristic wavelength and frequency • Electromagnetic spectrum - all types of electromagnetic wave energy, from very low frequency to very high frequency

Optical Telescope • Microscopes use lenses collect visible light from small objects and produce images that are much larger • Optical telescopes work the same way, using lenses or mirrors to collect visible light • The only difference is that the light comes from a very large and distant object • It then makes the distant object look larger and closer

Optical Telescopes • Refracting telescope – uses lenses to collect and focus visible light • Reflecting telescope – uses mirrors to collect and focus visible light

Optical Telescopes • The larger a mirror or lens, the larger the image it can make • But, if they get too big, they bend from their own weight • The telescope with the largest single mirror (5 m in diameter) is in the Hale Observatory in California

Spectroscopes • A star’s visible light has a characteristic spectrum of light of different wavelengths because each chemical element in the star blocks particular wavelengths of light • By looking at a star’s spectrum, scientists can figure out what its chemical makeup is • A spectroscope contains a prism to separate the light and a small optical telescope to see the spectrum • Stars contain ~ 75% hydrogen and 22% helium

Radio Telescopes • Collect radio waves from space • Reflecting dish collects waves that are reflected to the antenna and then amplified • Good for studying quasars and pulsars and have helped us learn about our own galaxy

Activity • Work in pairs • Complete Skills Worksheet 25.1 • Please hand in completed worksheet by tomorrow – if necessary, finish for homework

Section 2 Characteristics of Stars • Objectives: • Relate the temperature of a star to its color • Explain how measurements of parallax are used to measure a star’s distance from earth • Contrast absolute magnitude and apparent magnitude • Interpret data from an H-R diagram

Skills Warm-up • Stars in the Sky • Make a list of the sun’s characteristics. • Which of these do you think are shared by all stars? • Which characteristics of the sun do you think are different from other stars?

Star Classification • Scientists classify stars according to : • Brightness • Color • Size • Mass

Color and Temperature • The color of a star is related to its temperature

Distance of Stars • Hold your finger in front of your face. • Look at it with your left eye closed. • Then look at it with your right eye closed. • Does your finger seem to move or change position relative to the background?

Distance of Stars • Now find an object across the classroom from you. • Look at it with your left eye closed. • Then look at it with your right eye closed. • Does this object move position as much as your finger did?

Distance of Stars • Parallax – apparent change in the position of an object due to change in position of the observer • Scientists use parallax to determine the distance of a star from earth • As earth moves around the sun, nearer stars appear to change position relative to more distant stars • The closer a star is to earth, the greater its apparent change of position • Measurements of change in position can be converted into measurements of distance

Distance of Stars • Distances of stars are so great - you can’t use any normal units of measurement • Scientists use light-years • The distance that light, travelling at a speed of 310,000 km per second, will cover in 1 year • Equal to 9.5 trillion km • Proxima Centauri – closest star to earth at 4.2 light-years • Most stars are hundreds of light-years away

Magnitude of Stars • Magnitude – brightness of stars • The brighter the star, the smaller its number of magnitude • A star with a magnitude of -2 is brighter than one with a magnitude of 2 • Apparent magnitude – a star’s brightness from earth • Doesn’t really tell you how much light is given off • Absolute magnitude – actual brightness of a star from a standard distance

Hertzsprung-Russell Diagram • Two scientists graphed a large number of stars based on their absolute magnitude (luminosity) and temperature • 4 Types of Stars: • Main Sequence – stars grouped in a diagonal band from hot/bright to cool/dim • Supergiants – very bright stars that range from cool to medium/hot • Red giants – medium bright but cool • White dwarfs – low magnitude but relatively hot

Section 3 Life Cycles of Stars • Objectives: • Explain how stars come into being • Describe the stages of a star’s lifecycle • Contrast the different ways in which high-mass and low-mass stars end their life cycles • Predict what will happen for the rest of the sun’s lifecycle

Skills Warm-up • The Life of Stars • List and describe each stage of the human life cycle. • How do you think the human life cycle is different from that of a star?

Star Lifecycle • Human life cycle lasts about 75 years • Born • Infant • Toddler • Child • Teenager • Adult • Senior citizen

Star Lifecycle • Stars are also born, then change and eventually die • Star life cycle lasts billions of years • Stars in the sky are at different stages • Our sun is about ½ way through its 10 billion year life cycle

Birth of a Star • Nebula – a cloud of gas and dust where stars are born • Made of mostly hydrogen with helium and dust • Gravity causes the spread out particles of matter to condense • Matter starts to heat up and becomes a protostar • Protostars don’t shine, but give off infrared energy • Eventually they become hot enough for fusion to occur and a star is born

Low Mass-Stars – mass is less than 5X that of the sun • Low-Mass Star Lifecycle: • Begins as a main-sequence star but gradually the supply of hydrogen is changed by fusion into helium • Red Giant stage – • core of star starts to collapse • becomes hotter and denser • helium is converted to carbon • short part of life cycle • Dwarf stage – • Star cools and collapses inward to be a white dwarf • Eventually no light is given off and is a black dwarf

High Mass-Stars – mass is more than 6X that of the sun • High-Mass Star Lifecycle: • Uses up hydrogen at a much faster rate • Supergiant stage – • Hydrogen runs out • Core collapses • Outer layers expand greatly • Supernova stage – • Pressure builds up and cause a massive explosion • When only tiny core of neutrons remains it becomes - • Neutron star – dense core of neutrons • Black hole – so dense and gravity so strong nothing can escape it

Section 4 Galaxies and Star Groups • Objectives: • Describe the 4 types of galaxies • Explain what a constellation is and how it differs from a galaxy or star cluster • Explain how scientists know the universe is expanding • Predict how the constellations will look in the distant future

Skills Warm-up • Lions and Tigers and ….. • When you look at the sky on a clear night, what shapes do the stars make? • Draw what they look like to you.

Galaxies • Galaxy – collection of stars, nebulae, gases, dust, and planets that move through space as a unit – held together by gravity • There are at least 10 billion galaxies in the universe – ours is the Milky Way

Types of Galaxies • Spiral – flat disk with a bulge in the middle • Have long spiral arms that swing out and rotate like a pinwheel • Contain large amounts of gas and dust • Example – Milky Way

Types of Galaxies • Barred Spiral – similar to spiral but arms are attached to a straight bar shape • Bar is much brighter and denser than the arms • Less common than spiral • Example – Sculptor Galaxy

Types of Galaxies • Elliptical – football shaped • Rotate differently than spirals – more slowly • Contain less gas and dust • Example – Maffei 1

Types of Galaxies • Irregular – don’t have regular shapes • Vary greatly in size • Least common type • Example – Small Magellanic Cloud

Constellations • Star patterns shaped like people, animals, or objects • There are 88 official constellations • The stars in constellations may look like they are close together from earth, but they are not • Constellations are important because • They help form a map of the sky • Locations are described in relation to constellations • Stars are named by which constellation they are in

Expansion of the Universe • Big Bang Theory : • 15 – 20 million years ago all matter in the universe was packed into one giant fireball • The fireball exploded, spreading matter and energy out in all directions • As matter cooled, the force of gravity pulled together the particles of matter to form stars and galaxies • The universe was born!!!

Expansion of the Universe • What’s the proof??? • TheDoppler Effect • The light waves from an object moving away from earth are spaced more widely apart than if it were standing still • The waves appear to have a longer wavelength than they really have and shift to the red end of the visible light spectrum • All other galaxies have a red shift in their spectrums which means they are moving away from earth

Stars and Galaxies