Chapter 3 Lesson 2 NotesSun and other Stars
For Cambridge- NB 93 has vocabulary and bellringer, Notes go on 94 and 96, and lesson 2 outline will go on NB 95
For Comprehensive- These are a copy of notes for you.
Lesson 2-1How Stars Shine
• A star is a large ball of gas held together by gravity with a core so hot that nuclear fusion occurs.
• Nuclear fusion occurs when the nuclei of several atoms combine into one larger nucleus.
Lesson 2-1How Stars Shine (cont.)
• Nuclear fusion releases a large amount of energy.
• A star shines because when energy leaves a star’s core, it travels throughout the star and radiates into space.
Lesson 2-2Spectra of the Sun and other stars provide information about stellar composition.
Composition and Structure of Stars
Lesson 2-2• There are three interior
layers of a typical star.
• When first formed, all stars fuse hydrogen into helium in their cores.
Composition and Structure of Stars(cont.)
Lesson 2-2• The radiative zone is a
shell of cooler hydrogen around a star’s core.
• In the convection zone, hot gases move toward the surface as cooler gases move down into the interior.
Composition and Structure of Stars(cont.)
Lesson 2-2Beyond the convection zone are the three layers of a star’s atmosphere—the photosphere, the chromosphere, and the corona.
Composition and Structure of Stars(cont.)
Lesson 2-2The photosphere is the apparent surface of a star, where light energy radiates into space.
Composition and Structure of Stars(cont.)
Lesson 2-2• The chromosphere
is the orange-red layer above the photosphere.
• The corona is the wide, outermost layer of a star’s atmosphere.
Composition and Structure of Stars(cont.)
Lesson 2-2Changing Features of the Sun:
Sunspots
• Cooler regions of magnetic activity
• Seem to move as the Sun rotates
• Number varies on an 11-year cycle
Digital Vision/PunchStock
Lesson 2-2Changing Features of the Sun:
Coronal Mass Ejections (CMEs)
• Huge gas bubbles ejected from the corona
• Larger than flares
• May reach Earth
• Can cause radio blackouts
NASA
Lesson 2-2Changing Features of the Sun:
Prominences and Flares
• Prominences—clouds and jets of gases forming loops into the corona
• Flares—sudden increases in brightness, often near sunspots or prominences
SOHO Consortium, ESA, NASA
Lesson 2-2Changing Features of the Sun:
The Solar Wind
• Caused by charged particles streaming away from the Sun
• Extends to the edge of the solar system
• Causes auroras
CORBIS
Lesson 2-3• Most stars exist in star systems bound by gravity.
• Many stars exist in large groupings called clusters.
• Stars in a cluster all formed at about the same time and are the same distance from Earth.
Groups of Stars
Lesson 2-4• Scientists classify stars according to their spectra.
• Though there are exceptions, color in most stars is related to mass.
Classifying Stars
Lesson 2-4Blue-white stars tend to have the most mass, followed by white stars, yellow stars, orange stars, and red stars.
Lesson 2-4The Hertzsprung-Russell diagramis a graph that plots luminosity against temperature of stars.
Lesson 2-4The y-axis of the H-R diagram displays increasing luminosity and the x-axis displays decreasing temperature.
Lesson 2-4Most stars exist along the main sequence.
Lesson 2-4The mass of a main-sequence star determines both its temperature and its luminosity