Our Sun Flashcards
Sun Facts
- Surface Temperature
- Central Temperature
- Mass
- Current Composition
- Surface temp = 5800K
- Central temp = 107 K
- Mass = 1030 kg
- Current composition:
- 92.1% H
- 7.8% He
Energy Production - Overview
Energy is produced by fusion in which, simply, hydrogen is converted into helium: •4H →He + energy
- (n.b. other fusion processes take place as well, some of which are more important for other types of stars)
- Because the total mass afterwards is less than the total mass before, then energy is released because: E = mc2
The Proton-Proton Chain: Step 1
Step 1:
- Two protons (hydrogen nuclei, 1H) interact producing:
- The hydrogen isotope deuteron (2H)
- A neutrino, ν
- A positron, e+
- Subsequently the e+ annihilates with an e- producing two gamma rays, γ
The Proton-Proton Chain: Step 2
Step 2
- The 2H nucleus from the first step collides with a third proton.
- A helium isotope 3He is formed and another gamma-ray photon is released.
The Proton-Proton Chain: Step 3
Step 3
- Two 3He nuclei collide
- A different helium isotope with two protons and two neutrons 4He is formed and two protons are released.
Why doesn’t the Sun collapse under its own weight?
Maintaining the balance:
- Because the Sun is not a solid object it retains it shape through a balance of forces.
- Gravity is trying to crush it
- Fusion is producing escaping energy which counteracts gravity
Note that this balance applies throughout the Sun, even though the actual temperatures and pressures will change enormously with radius.
Reason for the Suns surface moving up and down
- The Sun “rings” at a range of frequencies.
- Typical periods are around 5 minutes and result in the sun’s surface moving up and down about 10m.
How do we study the Solar Fusion process?
Solar neutrinos
- If we wish to check on the solar fusion process, then we need to use a neutrino telescope.
- This is because heat energy takes about 1 million years to reach the surface and so we need something more direct
- Neutrinos escape at the speed of light and reach the earth in 8 minutes.
Photosphere - General Information
- The outer layer from which all visible photons arise.
- Note the presence of Sun Spots (see later) and the effect called Limb Darkening (next slide).
Limb Darkening - General Information
Solar Granules - General Information
Chromospheres - General Information
- This may be considered to be the solar atmosphere. Very tenuous, and much hotter (25000K) than the photosphere (6000K).
- Normally invisible to the human eye except during Total Eclipses.
Solar Atmosphere - Information and Components
Solar Atmosphere - Temperature profile
The Corona - Is it smooth?
- The corona is far from smooth as this UV image shows.
- Coronal holes are even more visible in the X-ray band.
Sunspots - What are they?
- Regions of relative coolness in the photosphere.
- Remember the Stefan-Boltzman Law : radiated flux = σT^4
- They have intense magnetic fields (0.3Tesla) - some 5000 times stronger than the earth’s magnetic field – and this can be measured directly using the Zeeman effect
- Mapping the Sun’s magnetic field. Sunspots are normally made up of north and south magnetic polarities
Solar Rotation
- Period = 25d at the equator and 35d at the poles.
- This is known as differential rotation.
Butterfly Diagram - average latitude of Sunspots
Differential Rotation and Sunspots
Structures associated with the Sun’s magnetic field
Solar Prominence and Coronal Mass Ejection (CME)
- A huge solar prominence seen by the SOHO spacecraft in the UV.
- Material in the prominence reaches temperatures of millions (K).
- This material is often ejected out into interplanetary space.
The Earth’s Climate
- The relationship between solar activity and the earth’s climate is a subject of intense research.
- It is believed that even a 1% change in the amount of solar energy could have serious effects, perhaps producing ice ages.