9.1 Activities of the Sun that Affect Earth
The Sun is a massive sphere of hot gas consisting mainly of hydrogen and helium. Its dynamic atmosphere is divided into three main layers: the photosphere, chromosphere, and corona.
Structure of the Sun's Atmosphere
- Photosphere: The dense, visible surface layer of the Sun (temperature approx. $6,000\,^\circ\text{C}$).
- Chromosphere: The bright red layer above the photosphere, visible during a total solar eclipse ($10,000\,^\circ\text{C} - 20,000\,^\circ\text{C}$).
- Corona: The outermost, extremely high-temperature layer ($1\text{ to }2\text{ million }^\circ\text{C}$) forming a glowing halo around the Sun.
Solar Phenomena
- Granules: Grainy structures on the photosphere caused by convection currents of hot plasma rising and cooling.
- Sunspots: Darker, cooler regions on the photosphere ($3,700\,^\circ\text{C}$) formed due to strong localized magnetic field disruptions. They follow an **11-year solar cycle**.
- Prominences: Huge loops of glowing plasma trapped along intense magnetic lines above the photosphere.
- Solar Flares: Sudden, violent explosions of high-energy radiation (X-rays, gamma rays) and charged particles near sunspots.
- Coronal Mass Ejections (CME): Massive bursts of magnetized plasma ejected into interplanetary space at high speeds.
- Solar Wind: Continuous stream of energetic charged particles (protons and electrons) flowing outward into space from the Sun's corona.
9.2 Space Weather
Space weather refers to the dynamic environmental conditions in space between the Sun and the Earth, largely driven by solar activities.
Earth's Magnetosphere
The magnetosphere is a protective region surrounding Earth formed by the interaction between Earth's magnetic field and solar wind.
- Function: Acts as a biological shield that deflects energetic cosmic rays and solar radiation away from Earth.
- Shape: Compressed on the sunward side by solar wind pressure and elongated into a tail ("magnetotail") on the nightward side.
Formation of Auroras
When energetic solar wind particles collide with atmospheric gas molecules (nitrogen and oxygen) trapped near Earth's polar magnetic fields, they produce glowing light curtains called auroras.
- Aurora Borealis: Visible in Northern Hemisphere high-latitude polar regions.
- Aurora Australis: Visible in Southern Hemisphere high-latitude polar regions.
Impacts of Space Weather on Human Daily Life
- Satellite Disruptions: Solar flares and CMEs damage onboard microcircuits and cause satellite orbital decay due to increased atmospheric drag.
- Communication Interruptions: High-frequency (HF) radio signals and GPS/GNSS navigation positioning errors due to ionospheric disturbances.
- Power Grid Failures: Geomagnetic storms induce strong currents (GICs) that can trip grid transformers, causing widespread blackouts.
- Radiation Hazard for Astronauts & Aviation: Increased ionising radiation doses for astronauts in low-Earth orbit and high-altitude polar flight crews.