The Sun

1. The Sun

2. The Sun -Our sun is a medium sized star, of middle age, at 4.6 byo and 150 million km from earth. -It’s diameter is 1.35 million km-we could fit 1,000,000 Earths inside.

3. The Sun The Sun • The Sun is the largest object in the solar system, in both size and mass. • The Sun contains more than 99 percent of all the mass in the solar system, which allows it to control the motions of the planets and other objects.

4. The Sun Properties of the Sun • The solar interior is gaseous throughout because of its high temperature. • Many of the gases are in a plasma state, meaning that they are completely ionized and composed only of atomic nuclei and electrons. • The sun has 4 layers. Corona, chromosphere, photosphere and a core.

5. Layers of the Sun

6. Layersagain

7. The Sun The Sun’s Atmosphere The corona, which is the top layer of the Sun’s atmosphere, extends several million kilometers southward from the top of the chromosphere and has a temperature range of 1 million to 2 million degrees K.

8. The chromosphere, which is above the photosphere and approximately 2500 km in thickness, has a temperature of nearly 30 000 K at the top.

9. The Sun The Sun’s Atmosphere • The photosphere, approximately 400 km in thickness, is the lowest layer of the Sun’s atmosphere. • This is the visible surface of the Sun because most of the light emitted by the Sun comes from this layer. • The average temperature of the photosphere is about 5800 K.

10. The Core • The core is the center of the sun where nuclear fusion takes place. This converts Hydrogen into Helium. This releases enormous amounts of heat and light.

11. Solar prominence A prominence, sometimes associated with flares, is an arc of gas that is ejected from the chromosphere, or gas that condenses in the inner corona and rains back to the surface.

12. The Sun Solar Features • Coronal holes, often located over sunspot groups, are areas of low density in the gas of the corona. • Solar flares are violent eruptions of particles and radiation from the surface of the Sun that are associated with sunspots. • When these particles reach Earth, they can interfere with communications and damage satellites.

13. The Sun The Sun’s Atmosphere Solar Wind • Gas flows outward from the corona at high speeds and forms the solar wind. • Solar wind consists of charged particles, or ions, that flow outward through the entire solar system, bathing each planet in a flood of particles. • The charged particles are trapped in two huge rings in Earth’s magnetic field, called the Van Allen belts, where they collide with gases in Earth’s atmosphere, causing an aurora.

14. The Sun Solar Activity • The Sun’s magnetic field disturbs the solar atmosphere periodically and causes new features to appear in a process called solar activity. • Sunspots are cooler areas that form on the surface of the photosphere due to magnetic disturbances, which appear as dark spots.

15. The sun has an axis that it rotates on every days. (like Earth rotates on its axis) • The cycle of sunspots is on a 11.2 year interval

16. The Sun The Solar Interior • Fusion occurs within the core of the Sun where the pressure and temperature are extremely high. • Fusion is the combining of lightweight nuclei, such as hydrogen, into heavier nuclei. • In the core of the Sun, helium is a product of the process in which hydrogen nuclei fuse. • At the Sun’s rate of hydrogen fusing, it is about halfway through its lifetime, with about another 5 billion years left.

17. The Sun Solar Composition • The Sun consists of 70% hydrogen and 28% helium, as well as a small amount of other elements. • This composition is very similar to that of the gas giant planets. • The Sun’s composition represents that of the galaxy as a whole.

18. The Sun Section Assessment 1. Match the following terms with their definitions. ___ photosphere ___ corona ___ chromosphere ___ sunspot D B A C A. the middle layer of the Sun’s atmosphere B.the outermost layer of the Sun’s atmosphere C.cooler region on the Sun’s surface that forms due to magnetic irregularities D. the lowest layer of the Sun’s atmosphere

19. End of Section 1

20. Measuring the Stars Objectives • Describe star distribution and distance. • Classify the types of stars. • Summarize the interrelated properties of stars. Vocabulary • constellation • binary star • parallax • apparent magnitude • absolute magnitude • luminosity • Hertzsprung-Russell diagram • main sequence

21. Measuring the Stars Groups of Stars • Constellation-A group of stars that form a pattern. • There are 88 constellations. • They are named after animals, mythological characters, or everyday objects. • Circumpolar constellations can be seen all year long as they appear to move around the north or south pole. Ex-Big Dipper • Summer, fall, winter, and spring constellations can be seen only at certain times of the year because of Earth’s changing position in its orbit around the Sun.

22. Measuring the Stars Groups of Stars Binaries • A binary star is two stars that are gravitationally bound together and that orbit a common center of mass. • More than half of the stars in the sky are either binary stars or members of multiple-star systems. • Astronomers are able to identify binary stars through several methods. • Accurate measurements can show that its position shifts back and forth as it orbits the center of mass. • In an eclipsing binary, the orbital plane of a binary system can sometimes be seen edge-on from Earth.

23. Measuring the Stars Stellar Position and Distances • Astronomers use units of measure for long distances. • A light-year (ly) is the distance that light travels in one year, equal to 9.461 × 1012 kmor 9,461,000,000,000 km

24. Measuring the Stars Stellar Position and Distances • To estimate the distance of stars from Earth, astronomers make use of the fact that nearby stars shift in position as observed from Earth. • Parallax is the apparent shift in position of an object caused by the motion of the observer. • As Earth moves from one side of its orbit to the opposite side, a nearby star appears to be shifting back and forth.

25. Measuring the Stars Basic Properties of Stars • The basic properties of stars include diameter, mass, brightness, energy output (power), surface temperature, and composition. • The diameters of stars range from as little as 0.1 times the Sun’s diameter to hundreds of times larger. • The masses of stars vary from a little less than 0.01 to 20 or more times the Sun’s mass.

26. Measuring the Stars Basic Properties of Stars Magnitude • One of the most basic observable properties of a star is how bright it appears. • The ancient Greeks established a classification system based on the brightnesses of stars. • The brightest stars were given a ranking of +1, the next brightest +2, and so on.

27. Measuring the Stars Basic Properties of Stars Apparent Magnitude • Apparent magnitude is based on the ancient Greek system of classification which rates how bright a star appears to be. • In this system, a difference of 5 magnitudes corresponds to a factor of 100 in brightness. • Negative numbers are assigned for objects brighter than magnitude +1.

28. Measuring the Stars Basic Properties of Stars Absolute Magnitude • Apparent magnitude does not actually indicate how bright a star is, because it does not take distance into account. • Absolute magnitude is the brightness an object would have if it were placed at a distance of 10 pc.

29. Measuring the Stars Basic Properties of Stars Luminosity • Luminosity is the energy output from the surface of a star per second. • The brightness we observe for a star depends on both its luminosity and its distance. • Luminosity is measured in units of energy emitted per second, or watts. • The Sun’s luminosity is about 3.85 × 1026 W.

30. Measuring the Stars Spectra of Stars • Stars also have dark absorption lines in their spectra and are classified according to their patterns of absorption lines.

31. Measuring the Stars Spectra of Stars H-R Diagrams • A Hertzsprung-Russell diagram, or H-R diagram, demonstrates the relationship between mass, luminosity, temperature, and the diameter of stars. • An H-R diagram plots the absolute magnitude on the vertical axis and temperature or spectral type on the horizontal axis.

32. Measuring the Stars Spectra of Stars H-R Diagrams • The main sequence, which runs diagonally from the upper-left corner to the lower-right corner of an H-R diagram, represents about 90 percent of stars. • Red giants are large, cool, luminous stars plotted at the upper-right corner. • White dwarfs are small, dim, hot stars plotted in the lower-left corner.

33. Measuring the Stars Spectra of Stars H-R Diagrams

34. Measuring the Stars Groups of Stars Star Clusters • Although stars may appear to be close to each other, very few are gravitationally bound to one other. • By measuring distances to stars and observing how they interact with each other, scientists can determine which stars are gravitationally bound to each other. • A group of stars that are gravitationally bound to each other is called a cluster. • In an open cluster, the stars are not densely packed. • In a globular cluster, stars are densely packed into a spherical shape.

35. Measuring the Stars Section Assessment 1. Match the following terms with their definitions. ___ binary star ___ absolute magnitude ___ luminosity ___ parallax B C A D A. the energy output from the surface of a star per second B.when two stars are gravitationally bound and orbit a common center of mass C.the brightness an object would have if placed at a set distance D. an apparent shift in the position of an object caused by the motion of the observer

36. Measuring the Stars Section Assessment 2. How can astronomers measure the speed at which a star is moving? Spectral lines are shifted in wavelength by motion between the source of light and the observer. If a star is moving toward the observer, spectral lines are blueshifted. If a star is moving away, spectral lines are redshifted. The higher the speed, the larger the shift.

37. Measuring the Stars Section Assessment 3. Identify whether the following statements are true or false. ______ The full Moon has less brightness than Venus on the absolute magnitude scale. ______ Luminosity of stars is a relatively consistent stellar property. ______ Around two-thirds of the stars in the sky are either binary stars or members of multi-star systems. ______ The Sun is part of the main sequence. true false false true

38. End of Section 2

39. Stellar Evolution Objectives • Explain how astronomers learn about the internal structure of stars. • Describe how the Sun will change during its lifetime and how it will end up. • Compare the evolutions of stars of different masses. Vocabulary • nebula • protostar • neutron star • supernova • black hole

40. Stellar Evolution Basic Structure of Stars • The mass and the composition of a star determine nearly all its other properties. • Hydrostatic equilibrium is the balance between gravity squeezing inward and pressure from nuclear fusion and radiation pushing outward. • This balance, which is governed by the mass of a star, must hold for any stable star; otherwise, the star would expand or contract.

41. Stellar Evolution Basic Structure of Stars Fusion • Inside a star, the density and temperature increase toward the center, where energy is generated by nuclear fusion. • Stars on the main sequence all produce energy by fusing hydrogen into helium, as the Sun does. • Stars that are not on the main sequence either fuse different elements in their cores or do not undergo fusion at all.

42. Stellar Evolution Basic Structure of Stars Fusion • Fusion reactions involving elements other than hydrogen can produce heavier elements, but few heavier than iron. • The energy produced according to the equation E = mc2 stabilizes a star by producing the pressure needed to counteract gravity.

43. Stellar Evolution Stellar Evolution and Life Cycles • A star changes as it ages because its internal composition changes as nuclear fusion reactionsin the star’s core convert one element into another. • As a star’s core composition changes, its density increases, its temperature rises, and its luminosity increases. • When the nuclear fuel runs out, the star’s internal structure and mechanism for producing pressure must change to counteract gravity.

44. Stellar Evolution Stellar Evolution and Life Cycles Star Formation • A nebula (pl. nebulae) is a cloud of interstellar gas and dust. • Star formation begins when the nebula collapses on itself as a result of its own gravity. • As the cloud contracts, its rotation forces it into a disk shape. • A protostar is a hot condensed object that forms at the center of the disk that will become a new star.

45. Stellar Evolution Stellar Evolution and Life Cycles Star Formation

46. Stellar Evolution Stellar Evolution and Life Cycles Fusion Begins • Eventually, the temperature inside a protostar becomes hot enough for nuclear fusion reactions to begin converting hydrogen to helium. • Once this reaction begins, the star becomes stable because it then has sufficient internal heat to produce the pressure needed to balance gravity. • The object is then truly a star and takes its place on the main sequence according to its mass.

47. Stellar Evolution The Sun’s Life Cycle • What happens during a star’s life cycle depends on its mass. • It takes about 10 billion years for a star with the mass of the Sun to convert all of the hydrogen in its core into helium. • When the hydrogen in its core is gone, a star has a helium center and outer layers made of hydrogen-dominated gas. • Some hydrogen continues to react in a thin layer at the outer edge of the helium core.

48. Stellar Evolution The Sun’s Life Cycle • The energy produced in the thin hydrogen layer forces the outer layers of the star to expand and cool and the star becomes a red giant. • While the star is a red giant, it loses gas from its outer layers while its core becomes hot enough, at 100 million K, for helium to react and form carbon. • When the helium in the core is all used up, the star is left with a core made of carbon.

49. Stellar Evolution The Sun’s Life Cycle A Nebula Once Again • A star of the Sun’s mass never becomes hot enough for carbon to react, so the star’s energy production ends at this point. • The outer layers expand once again and are driven off entirely by pulsations that develop, becoming a shell of gas called a planetary nebula. • In the center of a planetary nebula, the core of the star remains as a white dwarf made of carbon.

50. Stellar Evolution The Sun’s Life Cycle Pressure in White Dwarfs • A white dwarf is stable because it is supported by the resistance of electrons being squeezed close together and does not require a source of heat to be maintained. • A star that has less mass than that of the Sun has a similar life cycle, except that helium may never form carbon in the core, and the star ends as a white dwarf made of helium.