Essential Question

1. Objectives Describe how astronomers determine the composition and surface temperature of a star.Explain why stars appear to move to an observer on the earth. Essential Question How do astronomers determine the composition and surface temperature of a star? How do stars appear to move to an observer on the earth?

2. Star circumpolar Red shift Light years Parallax Apparent magnitude Absolute magnitude H-R diagram Main sequence stars Giants Supergiants White dwarfs Chapter 27.1 Vocabulary

3. Characteristics of stars The sun is our closest star A star is a body of gas that gives off a tremendous amount of light and heat From earth stars look like tiny white lights, but if you look closely they shine different colors (blue, yellow, orange, red and white) Stars also vary in mass and composition Chapter 27.1 NotesDescribe how astronomers determine the composition and surface temperature of a star.

4. Composition and temperature The light of stars is analyzed through a spectrometer, which breaks the light into different wavelengths or colors The display of colors and lines is called the spectrum There are three types of spectra; emission (bright light), Absorption (dark line) and continuous Chapter 27.1 NotesDescribe how astronomers determine the composition and surface temperature of a star.

6. Composition and temperature The dark lines are what tell us what makes up a star, the types of materials that can found in the star Stars are mainly Hydrogen and Helium, but also have carbon, oxygen, nitrogen, and calcium The temperature range of stars is 2,800c to 24,000c, with some blue stars reaching 50,000c Chapter 27.1 NotesDescribe how astronomers determine the composition and surface temperature of a star.

8. Motion There are two types of motion with stars apparent and actual Actual motion can be seen with only high powered telescopes, because of the great distances Apparent motion can be seen every night as you see stars move across the sky Stars also appear to shift as our seasons change or as we move around the sun they become visible to us Chapter 27.1 NotesExplain why stars appear to move to an observer on the earth.

9. Motion Star have three actual motions First they turn on there axis Second, most rotate around another star Third, they move toward or away from earth There are some stars that seem to always be out or never drop below the horizon, these are the circumpolar or the little dipper Light has a Doppler effect just like sound Blue means, it is moving closer to you Red means, it is moving farther away from you Chapter 27.1 NotesExplain why stars appear to move to an observer on the earth.

10. Star distance is measured in light-years Light travels at 300,000 km/s or in one year 9.5 trillion miles The closest star neighbor is Proxima Centauri at 4.2 light years, Sirius the brightest star at night is 9 light years, and Polaris or Northern Star is 700 light years away Distance is measured using a process known as parallax The shift of a star from January to June can be used to determine distance to within 1,000 light years The closer a star is the big the shift Chapter 27.1 NotesName and describe the way astronomers measure the distance from the Earth to the stars.

11. Distance to the stars Another method is to use the brightness of stars – for more distance stars They estimate the true brightness by using the spectrum They then compare it to its apparent brightness Cepheid are stars that pulse in brightness on a cycle of time From 1 day to 100 days The longer the cycle the brighter the star Chapter 27.1 NotesName and describe the way astronomers measure the distance from the Earth to the stars..

12. Stellar Magnitudes We can see about 6,000 stars with our eyes A good telescope will allow you to see about 3,000,000,000 (billion) stars The Hubble telescope can see about 1,000,000,000,000 (Trillion) stars Stars are broken into two different skills, how bright they appear from earth and the other measure is how bright they would be if all stars were the same distance Chapter 27.1 NotesName and describe the way astronomers measure the distance from the Earth to the stars.

13. Apparent Magnitude This is how bright a star appears from earth Chapter 27.1 NotesExplain the difference between absolute magnitude and apparent magnitude.

14. Absolute Magnitude This is how bright the star would be if it was 32.6 light years away from the earth If we take the sun with an apparent magnitude of -26.8 and moved it 32.6 light years away, it would have an absolute magnitude of +5 So if the apparent is less (-26.8) then the absolute (+5) the star is closer then 32.6 light years If the apparent is (+6) more then the absolute (+2) the star is farther then 32.6 light years 3.26 is one parsec – a star that has a parallax of one second Chapter 27.1 NotesExplain the difference between absolute magnitude and apparent magnitude.

15. Classification of stars When you classify stars by there temperatures and absolute magnitude a pattern develops The line through the graph is called the main sequence of stars, most stars visible at night are in this group It starts in the lower right hand corner with cool, dim and red stars It then moves up to the upper left corner with hot, bright, and blue stars The upper right is cool bright stars The lower left are hot and dim stars, called white dwarfs (about the size of earth) Chapter 27.1 Notes

16. Classification of stars Chapter 27.1 Notes

17. Chapter 27 activity • Procedure • Stand directly in front of and directly facing the red cup at a distance of several meters. • Close one eye and sketch the position of the red cup relative to the background and white cups. • Take several steps back and to the right of your original position, repeat step 2 • Take several steps directly back and make another sketch. • Repeat step 4 once again.

18. Chapter 27 activity - analysis • Compare your drawings. Did the red cup change position as you viewed it from different locations? Explain • What kind of results would you expect if you continued to repeat step 5 at greater and greater distances? Explain • If you noted the positions of several stars with a powerful telescope, what would you expect to observe about their positions if you sighted the same stars several months later? Explain

19. Notes 27.2 • Describe how a protostar develops into a star • Explain how a main sequence star generates energy • Describe the possible evolution of a star during and after the giant stage

20. Nebula Protostar Planetary nebula Novas Supernova Neutron star Pulsars Black hole Chapter 27.2 Vocabulary

21. Stellar Evolution Nebula – a cloud of gas and dust Protostar – a shrinking spinning region of gas that flattens into a disk with a central concentration Stars exists for billions of years. Stars form in nebula that usually are composed of 70% hydrogen, 28% helium, and 2% heavier materials. Gravity pulls it all together. Matter gets warmer with increased pressure, Over millions years, until 10,000,000C fusion begins. More than one star can form, as well as planets Chapter 27.2 Notes Describe how a protostar develops into a star

22. Main Sequence stars Second and longest stage of a stars life Energy generated in the core through fusion of hydrogen into helium, 1g of hydrogen can generate enough power to keep a 100 watt bulb burning for 3,000 years. The energy bubbles upward like boiling water, gravity prevents the expansion of the star. These two forces keep the star at a stable size, as long as it has enough hydrogen to convert to helium. Chapter 27.2 NotesExplain how a main sequence star generates energy

23. Giants & Supergiant Third stage of a stars life All atoms of hydrogen have fused into helium; therefore the core will contract under the force of gravity. Temp increases and helium fusion begins, carbon formed Hydrogen fusion continues in the areas surrounding the core and the star expands into a giant: 10 or more times larger then our sun, a supergiant is 100 times Chapter 27.2 Notes Describe the possible evolution of a star during and after the giant stage

24. White Dwarf Stars Planetary nebula – a expanding shell of gas left from a dying star. The end of helium fusion is the end of the giant stage of a medium size star. The outer gas layers are lost and the core revealed, it will heat and illuminate the expanding gases. It takes billions of years for a white dwarf to cool into a black or brown dwarf, the universe is too young to have any in it yet. Chapter 27.2 Notes Describe the possible evolution of a star during and after the giant stage

25. Novas Nova – a white dwarf that explodes as it cools, becoming a thousand times brighter for a short time. Some white dwarfs do not just cool, they have one or more large explosions. Astronomers think this may be caused by a companion star that is having material taken from it by the white dwarf. Chapter 27.2 Notes Describe the possible evolution of a star during and after the giant stage

26. Supernovas Supernova – a star that explodes with such tremendous force that it blows itself apart. A star with 10 to 100 times of our sun and the explosions can be 100 times brighter than novas. They can release as much energy as our sun would over 500 million years. These massive stars continue to fuse heavier materials until the core turns into iron, this core then contracts from gravity and explodes Chapter 27.2 Notes Describe the possible evolution of a star during and after the giant stage

27. Neutron Stars Neutron star – an extremely small and dense ball of neutrons. Pulsars – two beams of radiation that sweep across space like a lighthouse Formed from a supernova, as the star collapses only neutrons are left. A spoonful would weigh 100 million tons on earth Some give off radiation at the poles called pulsars, we can detect these as radio waves. Chapter 27.2 Notes Describe the possible evolution of a star during and after the giant stage

28. Black Holes Black hole – a hole in space with such gravity that light can not escape The most massive stars form black holes They are invisible to the eye, astronomers look for companion stars that are influenced by the gravity or the energy of the materials being pulled into the Black Hole Massive Black holes may be at the center of galaxies. Chapter 27.2 Notes Describe the possible evolution of a star during and after the giant stage

29. Notes 27.3 • Describe the characteristics that identify a constellation • Describe the three main types of galaxies • Explain the big bang theory

30. Constellations Galaxies Spiral galaxy Barred spiral galaxy Elliptical galaxy Irregular galaxy Open cluster Globular clusters Binary stars Quasars Chapter 27.3 Vocabulary

31. Star Groups Constellations You see what appear to be single stars, yet only 1 in 4 is actually a single star. 1/3 are double and the rest are triple or more star groups or clusters. Constellation – a pattern of stars There are 88 recognized constellation. They are used as a star locator map, the star are labeled by apparent magnitude and the constellation they appear in. Some stars are bright enough to have been given their own names - Antares Chapter 27.3 Notes

32. Galaxies Galaxy – A large scale group of stars The major component of the universe, a typical galaxy is 100,000 light years in diameter and has about 100 billion stars. Galaxies also contain gas and dust or nebulae, some are bright because they reflect light or from the gas within them. The dark areas absorb light from distant stars. Estimates of 50 billion to 1 trillion galaxies in the known universe. Chapter 27.3 Notes

33. Galaxies Types of Galaxies The two closest to the Milky Way is the large Magellanic Cloud and the small Magellanic Cloud at 150,000 light years There are 17 other galaxies within 3 million light years and this makes up the Local Group. Spiral galaxy - Barred spiral galaxy - Elliptical galaxy - Irregular galaxy - Chapter 27.3 Notes

34. The Milky Way Our sun is one of billions stars that circle the galactic center. It is 2,000 light years thick at the center. We are 30,000 light years from the center in a spiral arm. We revolve around the center at 250km/s, it takes 200 million years to complete a revolution Chapter 27.3 Notes

35. Star Cluster Binary stars Open clusters - Globular clusters - Difference – globular clusters have more stars, are in the core of the galaxy and a spherical shape. Open cluster are a loose grouping and are in the spiral arms. Binary stars - Used to determine stellar mass Consist of two stars, a multiple star system has more then two in orbit around each other. Chapter 27.3 Notes

36. Formation of the Universe The big bang theory – that the universe formed from a single point of matter. Then 12 to 15 billion years ago the “Big Bang” occurred propelling matter and energy outward in all directions. As they moved away from the center gravity began to have an effect and formed galaxies Quasars – These may be the oldest objects in our universe Chapter 27.3 Notes

37. Sun Diagram Page 575