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