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CHAPTER 28 STARS AND GALAXIES. 28.1 A CLOSER LOOK AT LIGHT  Light is a form of electromagnetic radiation, which is energy that travels in waves.  Waves.

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Presentation on theme: "CHAPTER 28 STARS AND GALAXIES. 28.1 A CLOSER LOOK AT LIGHT  Light is a form of electromagnetic radiation, which is energy that travels in waves.  Waves."— Presentation transcript:


2 28.1 A CLOSER LOOK AT LIGHT  Light is a form of electromagnetic radiation, which is energy that travels in waves.  Waves of energy travel at 300,000 km/sec (speed of light  Ex: radio waves and x-rays

3  Electromagnetic radiation waves are arranged into a continuum call the electromagnetic spectrum.  Wide range of wavelengths  Long wavelengths with low frequencies at one end, short wavelengths with high frequencies at the other end  Wavelength measured crest to crest/trough to trough  Frequency the number of that crests of the same wavelength that pass a point in one second.

4  Scientists study the visible light portion of the electromagnetic spectrum.  Spectra of a stars allow for astronomers to learn about the star’s elements and motion.  Spectra studied using a spectroscope

5  Three types of visible spectra  Continuous spectrum: unbroken band of colors, emitting all colors of visible light  Emission spectrum: unevenly space of lines of different colors, emitting light of only some Wavelengths  Absorption spectrum: dark lines that cross a continuous spectrum.

6  Doppler Effect - change in the wavelength of sound due to motion between the object and the receiver.

7  Doppler effect applies to lights as well as sound.  Shift of the emission spectra can indicate if the object is moving towards or away from Earth  Shift towards red end of spectrum, object moving away Earth – Redshift  Shift towards blue end of spectrum, object moving towards Earth - Blueshift  Doppler effect determined that the universe is expanding

8 TELESCOPES  Optical Telescopes – gather far more light than an unaided eye and magnify imagers  Reflecting  Uses one lens at back to gather and focus light  Image reflected on to a small mirror and then the eye piece  Refracting  Uses two lenses  Lens at the front gathers light  Eyepiece magnifies image

9  Radio Telescopes = big satellite dishes  Use to detect energy waves at frequencies lower than visible light  Other  Usually satellites in space  Gamma ray  Background radiation  X-ray  Hubble (infrared)

10 28.2 Stars and Their Characteristics  Observation of stars has been going on for over 5000 years  The grouping of stars are called constellations  Constellations  only appear together as viewed from Earth; from a different angle they do not look like the constellation

11  Constellations (continued)  Constellations will change shape over thousands of years due to the universe expanding  Move across the sky from east to west (though Earth rotates west to east)

12  North Star – Current is Polaris  Sits directly over the North pole  Does not move to the naked eye  Very powerful tool for navigation  Due to Precession, Polaris will not always be the “North Star”

13  The Constellations that dominate the night sky change from month to month. This is the result of the Earth’s change in position as it orbits the Sun.

14  Distances to stars and other objects in space  Astronomical Unit (AU) - the distance from Earth to the Sun (150 million kilometers)  Light year - the distance light travels in one year (9.5 trillion kilometers)  It is a distance measurement  Example - 4.2 light-years means that the light we see has been traveling for 4.2 years before we can see it (4.2 X 9.5 trillion km)  Parallax - change in an object’s direction due to a change in the observer’s position  Parsec short for “parallax second” equal to 3.258 light- years.

15 Parallax The further the object from the viewer, the less the parallax shift.

16  Stars  No two stars have the same proportions of elements  Elements  Hydrogen ~69%  Helium ~29%  Heavier elements ~2%  light that radiates is dependent on composition and temperature, this differs in every star  Star spectrum is its fingerprint

17  Mass, Size and Temperature  Stars vary greatly in masses, size and temperature  Cannot observe directly so we are estimating what the mass might be  Gravitational effect on bodies around the star help with estimating its mass  Star mass is expressed as multiples of the mass of our Sun (which has a stellar mass of 1)  Size varies more than mass  Smallest stars are smaller than Earth  Largest have diameters more than 2000 times that of our Sun  Stars differ even more in density  Betelguese is about one ten-millionth of our Sun  One star is so dense that one teaspoon would weight more than a ton on Earth

18 Star size comparison

19  Temperature of stars vary  Range of color emitted is dependent on the surface temperature  Cool stars are red  Ex. Betelguese with a surface temperature of 3000 o C  Mid-temperatures are yellow  Ex. The Sun with a surface temperature of 5500 o C  Hot stars are blue  Ex. Sirus  Harvard Spectral Classification Scheme - group stars by temperature and color


21  Luminosity = brightness of a star  Dependent on size and temperature of the star  If two stars are the same size the hotter star would be more luminous  Apparent magnitude - how bright a star appears  Does not factor in distance  Absolute magnitude - how bright the star would be if all stars were the same distance from Earth (10 parsec)

22  Variable stars - show a variation in brightness  Cepheid variables are yellow supergiant stars with a cycle of brightness ranging from 1- 50 days.  Most have a cycle of 5 days.  Nonpulsating star change in brightness due to fact that it is more than one star.

23 28.3 LIFE CYCLE OF STARS  Hertzsprung-Russell (H-R) diagram – shows luminosity, temperature, and stages in the life cycle of the stars  Main Sequence – 90% of stars run in a band from upper left to bottom right of diagram  Giants & Supergiants – more luminous, found above main sequence  White dwarfs – near the end of their lives, below main sequence, glowing stellar core

24 Hertzsprung-Russell Diagram 

25 Life cycle of a star like our Sun  A star begins its life in a cloud of gas ( mostly Hydrogen) and dust called a nebula  nebula condenses, becomes denser, temp. increases  becomes a protostar  fusion begins and star is “born”  Hydrogen in core continues to fuse into helium  When hydrogen “runs out”, fusion occurs outside the core and the star expands (giant)  Gas layers are blown away and the carbon- oxygen core is left (a white dwarf)

26 Life cycle of a Massive Star  Begins like our sun  Instead of a carbon-oxygen core forming, an iron nuclei forms, and the star expands to 100x the size of our sun (supergiant)  Iron nuclei absorbs energy and collapses (supernova)  Massive star remnants become a Neutron Star or Black Hole

27 (about 9 minutes)

28 Galaxies and the Universe  Universe – everything that exists, 10 billion-20 billion years old  Galaxy – group of stars held together by gravity  3 types:  We live in the Milky Way Galaxy ( a spiral galaxy)  Elliptical Galaxy- concentrated, spherical shape  Irregular Galaxy – smaller, fainter, spread unevenly


30 Origin of the Universe Big Bang Model – explains the history of the universe from a fraction of a second AFTER it came into being up to present time – Evidence supporting it = distance between galaxies is increasing (universe is expanding) – Edwin Hubble found redshifts in the spectra of the galaxies – Cosmic background radiation found with radio telescopes –

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