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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: plasmatemp. range 8,000,0002,000,000° 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- suncentered
• 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 (16421727)
• 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