The Sun and the Solar System

Chapter 26

24.3 Sun’s Size, Heat and Structure

• Diameter= 1,400,000 km or 868,000 miles– More than 3x the distance of Earth to moon– More than 1 million Earth’s could fit in sun

• Energy– All stars get their energy from fusion– Fusion- combining of nuclei of lighter

elements to form a heavier element– Star is place of intense heat and pressure

• Plasma- 4th state of matter consisting of charged particles (positively charged ions/ negatively charged electrons)

Fusion

-Mass before is greater than mass after

-Missing mass is converted to energy

Sun’s Layers

• Core: hydrogen and helium in a plasma state (15,600,000°C)

• Radiation zone: plasma- temp. range 8,000,000- 2,000,000° C)

• Convection zone: rising and falling currents of plasma that carry energy to the sun’s surface

Sun’s Layers cont…

• Photosphere: visible surface of sun– Granules- tops of convection

currents– ~6,000° C

• Chromosphere: inner layer of sun’s atmosphere– 20,000° C (reddish)– Solar prominences

• Corona: outer atmosphere– 1,000,000 to 3,000,000° C

• Examine the sun at different wavelengths.

Features on the Sun

• AU- astronomical unit- distance from sun to Earth (~150 million km)

• Sunspots- dark spots on photosphere– Dark because surrounding photosphere is hotter and

brighter– Magnetic field is 1000x stronger than surrounding

photosphere– Move from left to right

• Evidence that the sun rotates

– Cycle of about 11 years

Sunspots

Magnetic Field

Solar Wind and Magnetic Storms

• Solar wind- stream of electrically charged particles from corona– coronal holes- large openings– Solar flares- most explosive feature on the sun!

• Increase in sunspots= increase in solar flares

• Earth’s magnetic field deflects solar winds• Auroras- displays of color and light appearing in

upper atmosphere• Magnetic storms occur when more particles are

added to constant solar wind from corona– may disrupt radio communications

22.1 History of S.S.

• Geocentric- Earth-centered model– Celestial sphere that surrounded Earth– Used constellations for calendar– Planets closer to Earth than stars– Retrograde motion- moved eastward, then

westward for a few weeks

Important People

Ptolemy

• Greek astronomer in 2nd century AD

• Puzzled by retrograde motion

• Developed a system to predict planetary position

• Planets on epicycles- small circular orbits

• Deferent is the larger circular orbit

• Retrograde Motion

Important People

Nicolaus Copernicus

• Polish astronomer (1473- 1543)

• Developed heliocentric model- sun- centered

• Retrograde motion appears as Earth overtakes Mars

• Retrograde Motion

Important People

Tycho Brahe

• 16th century Danish noblemen

• Studied movements of planets in their orbits

• Very precise measurements without aide of telescope

• Passed away before he could apply data

Important People

Johannes Kepler• German; (1571-1630); Tycho’s assistant• Laws of planetary motion

– 1st- planets travel in elliptical orbits with sun at one foci

– 2nd- equal area law- a line connecting Earth to the sun will pass over equal area of space in equal times

– 3rd- harmonic law- the period (P) of a planet squared is equal to the cube of its mean distance (D) from the sun, or P2 = D3

– Kepler's Laws with animation

Important People

Isaac Newton

• English scientist and mathematician (1642- 1727)

• Developed explanation for what kept the planets in motion

• 3 laws of motion and law of gravitation– 1st law- an object will move forever in a straight line at

the same speed unless some external force changes its direction or speed

– Law of gravitation- every mass exerts a force of attraction on every other mass, and the strength of that force is proportional to each of the masses and inversely proportional to the distance between them

Important People

Galileo Galilei

• Italian scientist (1564-1642)• With the aide of the first known telescope

he discovered the following:– Four “Galilean” moons of Jupiter– Planets are circular disks, not just points of

light– Venus has phases just like the moon– The moon’s surface was not smooth– The sun has sunspots, or dark regions