Topic 1.3 - The Sun

• By using a telescope that lets only H-alpha wavelength through
• Allows active regions, prominences and filaments to be observed
• Allows just 0.01% of the light through

The safest way to observe the Sun is by projecting its image onto a white screen using binoculars or a small telescope. To improve contrast, direct rays should be blocked from hitting the screen by card. The objective lens should be partly covered by black card to prevent partial melting or permanent damage.

• Diameter: 1.4 million km
• Distance from Earth:  150,000 km
  
• The Earth orbits the Sun in an ellipse

• The visible light is 5800 K 
• Objects at this temp emit yellow light most strongly

• Chromosphere is lower atmosphere
• H atoms absorb energy from photosphere and reemit as reddish light
• Characterised by solar flares and prominences
• Using H-Alpha filter, we can see:
  • bright, hot regions called plages
  • dark, cool streaks - filaments (called prominence when viewed side-on)

• Corona is outer atmosphere
• Source of solar wind
• Extends several million km into interplanetary medium
• Only visible during total solar eclipse/using coronograph
• Temp reaches 2 million°C  (Hot enough to emit X-Ray)

• On photosphere
• Cooler, darker region where convection currents transferring heat to surface are stopped by strong, localised magnetic fields
• Central, dark - umbra - 4000K
• Less dark - penumbra - 5600K
• Varies 1000 - 50,000km (typically 10,000km)
• Can remain visible few days to several weeks
• Often occur in pairs 
• Often found in groups

• 25 days at equator

• 36 days at poles

• Sunspots observed over many days
  • position recorded
• Movement of one/a group
• Found by extrapolation

• 11yr cycle
• Begin at 35/40°N/S
• No. increases and positions drift towards equator as cycle progresses
• Majority occur at 5-10°
• No. of sunspots greatest halfway through cycle

• Energy from nuclear fusion reactions in core
• Hydrogen nuclei fuse to form helium nuclei
• Process called proton-proton chain
• Happens due to very high temps/pressures

• Visible: Only photosphere is seen
• 100km thick
• Granulated appearance caused by upwelling hot material
• Surrounded by sinking cool material (darker)
• Sunspots

• H-Alpha: Active regions, filaments & prominences
• X-Ray: Carried out from rockets/satellites
• Mainly see corona

• Stream of charged particles travelling at several 100km/s
• Fast enough to escape sun's gravity
• Charged particles trapped by magnetic field into Van Allen Belts
• When overloaded, particles cascade down to Earth
• Guided + accelerated to upper atmosphere causing aurorae