Our Sun & Nuclear Fusion

(Chapter 7)

Student Learning Objectives

• Compare properties of the Earth and Sun

• Describe the layers of the Sun and how energy is transported through each layer

• Analyze sunspots and solar activity.

What do we know about the Sun?

• 4 x 1026 Watts• 100 times hotter than Earth’s hottest summer day• 300,000 times more mass than Earth• 109 Earth diameters• 1,300,000 Earth volumes

Sun EarthSurface Temperature 9,944 °F 57.2 °F

Mass 1.988 x 1030 kg 5.976 x 1024 kgDiameter 1,392,000 km 12,756 kmDensity 1.5 g/cm3 5.5 g/cm3

Practice

The Sun is a low mass star. How does this star compare and contrast with our Earth?

Energy Transfer

Energy is transported from hot to cold, through the layers of a star, by two methods.

Radiation (light)

Convection (boiling)

What are the layers of the Sun?

The Sun has 6 distinctive layers.

The Layers

1. Core: energy production

2. Radiative Zone: photons

3. Convective Zone: boiling fluid

4. Photosphere: photons leave star

“Surface” of the Sun. Why?

Limb Darkening

Granulationobubbles size of Texas o last 10-20 minutes

5. Chromosphere: thin jets of gas called spicules

Transition ZoneTemperature spikes

6. Corona: solar wind

protons, electrons, & other small particles

Corona

Density and temperature change in the layers.

Practice

1) Why does the corona escape the Sun?

 

2) How do astronomers know the layers of the Sun? Hint: How do we know about the interior of the Earth?

What mechanism is responsible for sunspots?

A sunspot is a relatively cooler area on the surface of the Sun.

T = 4,240 Kelvin (8,155 ○F)  

Change in size

Last days or months

Appear in pairs and groups

Image Credit: APOD

Sunspots form where energy is disrupted by magnetic fields.

Differential rotations cause "kinks" in the magnetic field lines.

BabcockModel

Practice

1) A 60 Watt light bulb is 250 ○F. Would an 8,155 ○F sunspot be bright if it was isolated from the surrounding photosphere?

2) Challenge: How would the energies compare for the 60 Watt Light Bulb and a sunspot?

E = sT4

Different levels in the Sun rotate with different speeds and the surface rotates at different speeds.

Equator = 25 daysPoles = 27.8 days

The sunspot cycle peaks every 11 years.

Full Cycle = 22 years

http://spaceweather.com/

Maunder Minimum

There is an unexplained absence of solar activity recorded.

The Zeeman Effect shows strength of magnetic field.

Atom in magnetic fieldAtomic energy levels are split into sublevelsDegree of splitting shows strength

What are the features that indicate solar activity?

All activity observed on the surface of the Sun, and in the solar atmosphere, is caused by the Sun’s magnetic field.

Prominence

Filament Flare

Practice

Does solar activity affect us on Earth?

(2014)

How do stars produce photons?

The definition of a star is an object that has a core density great enough to sustain nuclear fusion.

Proton–Proton Chain

4 H He + energy

1 Second in Our Sun

About 1038 reactions take place

600 billion kg of hydrogen is converted into helium

4 billion kg of mass becomes energy

Practice

Our star will last another 5-6 billion years. How is this possible with so much mass loss each second?