Download Chapter 26 – The Sun and the Solar System

Chapter 26 – The Sun and the Solar System
I.
The Sun’s Size, Heat and Structure
A. Size
1. More than 1,000,000 earth’s would fit inside the sun
2. The sun’s diameter is 110 times the earth’s
3. Compared to other stars it is just average in size
4. If the sun was a bottle cap the largest star, Epsilon
Aurigae, would be the size of a football field
B. Sun’s Energy
1. Fusion – the combining of the nuclei of lighter elements to
form heavier elements is the source of energy of all stars
2. E = mc2 – this equation shows the relationship between
mass and energy
a. Matter can be converted into energy
3. Due to intense heat and pressure, atoms get torn apart into
the nuclei and electrons. This results in H & He existing
as a plasma
4. These nuclei normally repel each other, however, due
to their speed, over crowding and heat, they are forced
to fuse.
5. When 4 Hydrogen nuclei come together, they produce
a Helium nucleus. A by-product of this is energy.
C. Sun’s Layers
1. During the fusion reaction, energy is produced inside
the sun that pushes outward is balanced by the force of
gravity drawing the layers inward
2. Core – mostly plasma H & He
a. Temperature ≈ 15,600,000°C
3. Radioactive Zone – surrounds the core
a. Near the core ≈ 8,000,000°C
b. Near the convection zone (next layer) ≈ 2,000,000°C
4. Convection Zone – rising and falling currents carry energy
to sun’s surface
5. Photosphere – visible surface of the sun
a. Consist of granules – 1,000km wide, 20 minute life
b. Temperature ≈ 6,000°C
6. Inner atmosphere – chromosphere
a. Area where solar prominences take place
7. Outer atmosphere – corona – visible during total solar
eclipses
D. Features of the Sun
1. Sun is 150,000,000km away from earth, this distance is
known as an Astronomical Unit (A.U.)
2. Sunspots – Dark spots on the photosphere
a. Some are barely visible while others are 4 times larger
than Earth
b. Small one may last a few hour – large ones months
c. Are very hot and bright – look dark because the
photosphere is so much hotter and brighter than the
sunspots
d. Move from left to right across surface
i
This gave evidence that the sun rotates
e. An increase in sun spots may result in increased
solar flares, solar winds and auroras
f. Sunspot activity peaks every 11 years
3. Sun’s rotation
a. At the equator – 25 days
b. At the poles – 34 days
4. Solar winds – corona gives off a constant stream of
electrically charged particles
a. Mostly protons and electrons
b. The earth’s magnetic field will reflect most of them
p.514
c. Auroras – bright lights at the earth’s poles caused
by solar wind particles interacting with earth’s
magnetic field
d. Holes in the corona (coronal holes) and solar flares
are sources of solar winds
II.
Observing the Solar System: A History
A. The movement of Planets and Stars
1. As we watch the sun go across the sky it appears to move
as we stand still.
2. For 2,000 years it was the belief that the earth was the
center of the universe, it is called geocentric (earth
centered)
3. Stars were thought to have been holes in a celestial sphere
that surrounded earth. Behind the sphere was a source of
intense light.
4. The changing positions of constellations gave basics for
the 1st calendars
5. Some points were not fixed in constellation, they
wandered. Astronomists believe those point of lights were
closer (Planets)
6. Most of the time the planets move eastward however
they stop and then move west for a few weeks, then
back eastward, this is known as retrograde motion.
B. History of Astronomers
1. Ptolemy – lived in Egypt in the 2nd century AD
a. Geocentric Model – explained retrograde motion by the
use of epicycles – perfect spheres the planet revolved
on while on the planetary sphere
2. Copernicus
a. Polish astronomer (1473-1543) proposed a heliocentric
(sun centered) solar system
b. Could explain retrograde by the different speeds the
planets (including earth) went around the sun (p. 578)
3. Tycho Brahe
a. 16th century observational astronomer
b. made in-depth study of the moon and planets
throughout their orbits
c. identified a number of unexpected occurrence if the
orbits were round
d. Died before he could apply his data
4. Kepler
a. Used Tycho’s work and found out that the orbits were
elliptical rather than round
b. Created 3 laws of planetary motion
i 1st law – planets travel in elliptical orbits with the
sun at one focus
ii 2nd law – Planets travel faster when closer to the
sun
 this law is also known as the equal area law
 planets sweep out equal area in equal time
3rd Law or Harmonic Law – is used to find a
planets mean distance from the sun
Period2 = Distance3
 period – time taken to revolve around the sun
 distance – mean distance between the planet and
the sun
 The average speed of earth in its orbit is 30km/sec
5. Newton (1642 – 1727) English scientist mathematician
 Newton identifies gravity as the force that keeps
the earth in orbit around the sun
 The strength of gravity is proportional to the
masses and indirectly to their distance
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