Overview
This lecture explores the Sun's atmosphere and outer layers using various wavelengths of electromagnetic energy to reveal key solar features and phenomena invisible to the naked eye.
The Sun's Outer Layers
- The Sun’s corona is its outermost atmospheric layer, visible during total solar eclipses or through specialized instruments.
- The Solar Dynamics Observatory (SDO) uses extreme ultraviolet light to capture detailed images of the corona.
- Coronal holes are cooler, less dense regions where solar wind escapes more easily into space.
- Solar wind from coronal holes causes auroras on Earth when it interacts with Earth's magnetosphere.
Solar Phenomena
- Solar flares are huge explosions resulting from tangled magnetic fields, releasing intense electromagnetic radiation.
- Coronal mass ejections (CMEs) occur when magnetic fields snap, sending vast amounts of plasma into space.
- Solar filaments or prominences are loops of plasma extending from the Sun’s surface, sometimes lasting months.
- Coronal rain consists of cooled plasma falling back to the Sun’s surface from the corona.
Exploring with Different Wavelengths
- Different wavelengths of ultraviolet light reveal both "quiet" and active regions in the corona based on their temperature.
- Imaging in various wavelengths shows complex, interconnected solar events that might appear simple at first glance.
Sub-Atmospheric Layers
- The transition region is a thin layer between the corona and chromosphere, with temperatures rising from 8,000 to 500,000 Kelvin.
- The chromosphere is about 1,700 km thick, characterized by jets of plasma called spicules that are propelled up to 100 km/s.
- Spicules are formed with the help of neutral particles giving buoyancy to magnetically charged particles.
The Photosphere and Surface Features
- The photosphere, the Sun’s visible surface, is around 400 km thick and composed of plasma.
- Sunspots are cooler, dark regions caused by strong magnetic fields trapping heat below the photosphere.
- Solar flares often occur near or at sunspots.
- Solar granules are convection cells about 1,000 km wide, lasting about 20 minutes each, with hot plasma rising at the center and sinking at the edges.
Key Terms & Definitions
- Corona — The Sun’s outermost atmospheric layer, extremely hot and thin.
- Solar Flare — A large explosion on the Sun’s surface due to magnetic activity.
- Coronal Hole — An area where the Sun’s magnetic field opens to space, allowing solar wind to escape.
- Solar Filament/Prominence — Large loops of plasma on the Sun, visible in ultraviolet light.
- Coronal Mass Ejection (CME) — Massive burst of solar plasma and magnetic field into space.
- Transition Region — A thin, sharply-changing temperature layer between the corona and chromosphere.
- Chromosphere — The layer of the Sun’s atmosphere just above the photosphere.
- Spicule — Narrow jets of plasma rising from the chromosphere.
- Photosphere — The Sun’s visible surface layer.
- Sunspot — A temporary, cooler, dark spot on the photosphere with intense magnetic activity.
- Solar Granule — A convection cell on the Sun’s surface.
Action Items / Next Steps
- Observe the next total solar eclipse (April 8th, 2024) safely with certified eclipse glasses.
- Review the solar cycle and its impact on solar phenomena.
- Further reading: research the electromagnetic spectrum’s role in solar observation.