Lesson 5: Closer Look at the Sun, Nuclear Fusion in the Sun, Sun-Earth Connection

Question 1

Why does the sunshine? How do we know it’s not ‘on fire’ or due to ‘gravitational contraction’ ?

what is it powered by?

Answer 1

The Sun is powered by Nuclear Energy
E = mc^2

Question 2

state the two types of equilibrium within the Sun (or any star for that matter)?

also Gravitational contraction

Answer 2

Gravitational equilibrium: Gravity pulling in which balances pressure pushing out
* The sun is the prefect equilibrium for gravity pushing down and pressure pushing out

Energy balance: Thermal energy released by fusion in core balances radiative energy lost from surface

Gravitational contraction: provided energy that heated the core as the Suns as forming. Contraction stopped when fusion started

Question 3

How much larger is the Sun than Earth? How much more massive?

radius and mass that of Earth

Answer 3

Radius: 6.9×108 m (109 times Earth)
Mass: 2×1030 kg (300,000 Earths)

Question 4

What is the Sun’s structure? Be able to describe the different layers of the Sun, where they are located in relation to each other, and their temperatures.

Answer 4

Solar wind: a flow of charged particles from the surface of the Sun

Corona: outermost layer of solar atmosphere; temperature of 1 million K; very not dense and spread out

Chromosphere: middle layer of solar atmosphere; temperature of ~10^4-10^5 K

Photosphere: visible surface of the Sun; temperature of ~6000 K
○ Includes sunspots

Convection zone: Energy transported upward by rising hot gas

Radiation zone: energy transported upward by photons

Core: energy generated by nuclear fusion; temperature ~15 million K

Question 5

What are the two factors of Fusion?

Answer 5

Temperature and density

Question 6

Describe the basic structure of an atom, what a hydrogen atom is

Answer 6

An atom is a fundamental a particle that contains electrons (negative), protons (positive), neutrons (neutral)

Hydrogen has a proton and an electron (no neutron)

Question 7

What is a plasma? How is it different than a Gas?

Answer 7

Plasma: hot ionized gas
* stripped of one or more of their electrons — large quantity of free electrons and positively charged ions in the Sun, making it an electrically charged environment

Different from gas because:
Plasma is made up of groups of positively and negatively charged particles but particles of a gas are mostly uncharged.

Question 8

Do protons attract each other or repel each other? Why?

Answer 8

Since charges of the same sign repel, protons mutually repel each other

Question 9

What force keeps atomic nuclei together, instead of flying apart due to the repelling of all the protons?

Answer 9

The Strong Force holds Neutrons and Protons together
* But its limitation is far distance
At CLOSE distances (ie, within the nucleus), protons and neutrons attract

Question 10

What is a Helium atom made of?

Answer 10

The helium atom:
2 neutron
2 proton
2 electron

Question 11

What’s the difference between fission and fusion?

Answer 11

Fusion is the literal fusion of two particles together
○ Two or more protons coming together

Fission is the falling apart of atoms

Question 12

Why is fusion between protons only possible at the centres of the Sun (or stars in general)?

Answer 12

High temperatures enable nuclear fusion to happen in the core
At high speeds, protons/nuclei can fuse together.. Not low speeds

Question 13

What is the proton-proton chain? How does it create energy?

Answer 13

The proton-proton chain is how hydrogen fuses into helium in the Sun
* When two protons fuse together and make one proton, one neutron, one positron and neutrino

Overall reaction:
* IN: 4 protons
* OUT: 4He nucleus, 2 gamma rays, 2 positrons, 2 neutrinos
* **Total mass is 0.7% lower **
The resulting amount of material has turned into gamma rays

Question 14

While we have never been to the centre of the Sun, Nuclear Fusion would explain a variety of things we observe about the Sun. What are those things we observe?

Answer 14

• Contains helium
• Emit a full spectrum of light (the gamma-rays that are produced at the core by fusion are reduced in strength as they random walk their way out to the surface)
• Will live for billions of years! (the time it would take to fuse all of the hydrogen would take billions of years)

Question 15

discuss the Solar Thermostat theory.

Answer 15

Decline in core temperature causes fusion rate to drop, so core contracts and heats up
Rise in core temperature causes fusion rate to rise, so core expands and cools down

Question 16

Energy is created in the centre of the Sun, describe the pathway the photons take as they leave the core and move through the radiation zone of the Sun. Describe the
path the photons take once they make it into the convection zone of the Sun.

Answer 16

• Gamma rays bounce off the plasma (protons and electrons) in the radiation zone for a million years
• Energy gradually leaks out of the radiation zone in the form of randomly bouncing photons

Then:
Convection layer

• Convection: rising hot gas takes energy to the surface

Question 17

What is convection? How does it create the pattern we see on the photosphere of the Sun?

Answer 17

Convection (rising hot gas) takes energy to the surface)

• Bright blobs on photosphere where hot gas reaches the surface

Question 18

Describe how we are able to know what is happening inside the Sun, specifically related to neutrinos.

Answer 18

Neutrinos created during fusion fly directly through the Sun (don’t react with anything)
* Observations of these solar neutrinos can tell us what’s happening in the core

so
provides direct evidence that nuclear fusion occurs in the sun and the Sun’s current status

Question 19

What are Sunspots, Solar Flares, and Solar Prominences?

sunspots - also differential rotation

Answer 19

Sunspots: Are regions with strong magnetic fields
* Are cooler than other parts of the Sun’s surface (4000 K)
* Tracking sunspots has allowed us to measure the speed of rotation of the sun, which is not the same at all latitudes! This is called a Differential Rotation

Solar Flares: Magnetic activity causes solar flares that send bursts of x-rays and charged particles into space
* will travel through space

Solar Prominences: Magnetic activity also causes solar prominences that erupt high above the Sun’s surface
* the arch does not separate and go into space

Question 20

Compare the Sun’s magnetic field to Earths.

Answer 20

Larger, stronger, more active, the Sun’s magnetic field changes over time, excites/heats particles

• The Sun is a plasma, which is a fluid. Plasma is a cloud of charged particles
• The Sun rotates with different rates depending on the latitude

Question 21

Why doesn’t the Sun’s magnetic field act like a bar magnet? What does it end up acting like?

Answer 21

The sun’s magnetic field has two poles, like a bar magnet. The poles flip at the peak of the solar activity cycle, every 11 years.

• So, while the sun does have a magnetic field, with both a north and south pole like a bar magnet, it’s also very unlike a magnet and the Earth, because that magnetic field is complex, and changes dramatically over time

Question 22

What are coronal mass ejections?

Answer 22

Coronal mass ejections: send bursts of energetic charged particles out through the solar system

Question 23

How does the solar wind create aurora on Earth?

Answer 23

Auroras are the glow of the charged particles from solar winds which are interacting with Earth’s magnetic field and atmosphere (primarily near the poles, where Earth’s magnetic field is the strongest)

Question 24

Why are sunspots dark?

Answer 24

They appear dark because they are cooler than other parts of the Sun’s surface

Question 25

What is the solar cycle? What causes it? How do we know it’s occurring?

As well, define solar maxima and solar minima

Answer 25

Solar cycle: The Sun’s magnetic field goes through a cycle. Every 11 years or so, the Sun’s magnetic field completely flips.
* Sun’s north and south poles switch places

Caused by the the sun’s magnetic field

How do we know?
* In March of 1989, a geomagnetic storm caused a nine-hour outage of Hydro-Quebec’s electricity transmission system

• Heinrich Schwabe: Between 1826 and 1850 Schwabe kept daily records of the number of sunspots.
• Solar maxima (period when there is most sunspots; means the sun is more active) and solar minima (period when there is the least sunspots, means sun is less active)
• A drawing of the Sun made by Galileo Galilei on June 23, 1613 showing the positions and sizes of a number of sunspots. Galileo was one of the first to observe and document sunspots

Question 26

Does the solar cycle have any measurable affect on Earth’s climate? How much does the Sun’s luminosity vary over the solar cycle?

Answer 26

It is unclear whether the sunspot cycle affects Earth’s climate in any way, but it almost certainly is not responsible for global warming

the luminosity of our Sun varies a measly **0.1% over the course of the 11- year-solar cycle. **

Question 27

Does the Sun have a solid surface? What about its core?

Answer 27

The Sun does not have a solid surface or continents like Earth, nor does it have a solid core

Question 28

What is the effective temperature of the Sun?

Answer 28

5800 K

Question 29

What is the Sun’s atmosphere made of?

Answer 29

73% of the Sun’s mass is hydrogen, and 25% is helium.
* Other chemical elements are carbon, oxygen, and nitrogen, make up only 2%

(from the sun’s outer layers)

Question 30

What is the definition of a plasma?

Answer 30

hot ionized gas

Question 31

What are the layers of the Sun? Beginning from the core?

Answer 31

Core
Radiation
Convection
Photopshere
Chromosphere
Transition Region - temperature immediately rises
Corona

Question 32

Why is the radiative zone named that? Why is the convection zone named that?

Answer 32

Radiative zone: region above the core, primary mode for transporting energy
- high density of matter region, means a photon cannot travel too far without encountering a particle, causing it to change direction and lose some energy
- extends up to about 70% of the way to the surface

Convective zone: outermost layer of the solar interior, transports energy from the edge of the radiative zone to the surface through giant convection cells
- the plasma at the bottom of the convective zone is extremely hot, and it bubbles to the surface where it loses its heat to space

Question 33

What is the photosphere?

Answer 33

Photosphere: is the layer where the Sun becomes opaque and marks the boundary past which we cannot see
- Outside the Sun, we can observe only those photons (originally formed inside the Sun) that are emitted into the solar photosphere, where the density of atoms is sufficiently low and the photons can finally escape from the Sun without colliding with another atom

Question 34

Over what distance does the Sun’s atmosphere change from completely transparent to completely opaque?

Answer 34

The Sun’s atmosphere changes from transparent to opaque over just a few hundred kilometers
- photosphere is about 500 kilometers thick

Question 35

What is granulation? How does convection play a role in creating granulation?

Answer 35

Granulation: Observations with telescopes show that the photosphere (visible part) has a mottled appearance, resembling a pot of boiling oatmeal.

• The granular formation is due to the convective motion of the gas in the sub-photospheric layers, with the bright centre as upward flows and the dark lanes as downward flows

Question 36

What is the chromosphere? What is the transition region?
What is the corona?

Answer 36

Chromosphere: region of the Sun’s atmosphere that lies immediately above the photosphere

Transition region: the part of the Sun where the rapid temperature rise occurs

Corona: The hottest part of the solar atmosphere, which has a temperature of a million degrees or more

Question 37

What is the solar wind? What are aurora, and how are they generated?

Answer 37

Solar wind: Sun’s atmosphere is that it produces a stream of charged particles (mainly protons and electrons)

○ At the surface of Earth, we are protected to some degree from the solar wind by our atmosphere and Earth’s magnetic field. The magnetic field lines on Earth are at the north and south magnetic poles.
○ Here, charged particles accelerated by the solar wind can follow the field down into our atmosphere. As the particles strike molecules of air, they cause them to glow, producing beautiful curtains of light

Auroras: As the particles strike molecules of air, they cause them to glow, producing beautiful curtains of light

Question 38

What is a sunspot? What are its two parts?

Answer 38

Sunspots: are large, dark features seen on the surface of the Sun caused by increased magnetic activity
They look darker because the spots are cooler

• Consists of two parts: an inner darker core, the umbra, and a surrounding less dark region, the penumbra
  (like the moon in an eclipse)

Question 39

What was Galileo able to do by tracking sunspots?

Answer 39

A drawing of the Sun made by Galileo Galilei on June 23, 1613 showing the positions and sizes of a number of sunspots. Galileo was one of the first to observe and document sunspots

Question 40

What is differential rotation?

Answer 40

Differential rotation: the Sun rotates every 25 days at the equator and takes progressively longer to rotate at higher latitudes, up to 35 days at the poles

Question 41

What is the sunspot cycle? How did we figure out it existed?

Answer 41

Sunspot cycle: the number of sunspots varied systematically, in cycles about a decade long

Heinrich Schwabe, a German pharmacist and amateur astronomer, kept daily records of the number of sunspots.

Question 42

What is a sunspot minimum and sunspot maximum? How often do each occur?

Answer 42

• The beginning of a solar cycle is a solar minimum, or when the Sun has the least sunspots.
• Over time, solar activity—and the number of sunspots—increases. The middle of the solar cycle is the solar maximum, or when the Sun has the most sunspots.

Question 43

Is the time between successive maxima/minima always the same?

what is the average?

Answer 43

sunspot maxima occur at an average interval of 11 years

• but the intervals between successive maxima have ranged from as short as 9 years to as long as 14 years.

Question 44

Describe the Sun’s dynamo.

Answer 44

Dynamo: is a machine that converts kinetic energy (i.e., the energy of motion) into electricity.
○ is located in the convection zone