Overview
This lecture finished the discussion of the Sun's layers, focusing on the chromosphere and corona, and explained why the hottest parts of the Sun can paradoxically feel freezing cold due to low density.
Visibility of Sun's Outer Layers
- The photosphere outshines the outer layers, making them hard to see from Earth.
- Eclipses or special telescope techniques can block the photosphere to reveal higher layers.
The Chromosphere
- The chromosphere is the Sun’s layer just above the photosphere, appearing fire-like and colorful.
- "Chromosphere" means "color sphere" due to its colorful appearance.
- It is thinner and much hotter than the photosphere, at about 25,000 Kelvin (vs. 5,800 K for the photosphere).
- The chromosphere is made of hot jets of gas called spicules bursting from below the photosphere.
The Corona
- The corona is the Sun’s outermost layer, visible during eclipses as a crown around the Sun.
- "Corona" means "crown," describing its appearance.
- The corona is irregular in size and shape, expanding up to 2-3 times the Sun’s diameter.
- It is the thinnest layer but the hottest, at around 2 million Kelvin.
- Unlike density, which decreases steadily outward, temperature dips at the photosphere and then rises in the outer layers.
- The high temperature of the corona is not fully understood by scientists.
Heat and Density in the Corona
- Despite its extreme temperature, the corona’s low density means it would not transfer heat efficiently.
- You would freeze in the corona, not burn, because sparse particles do not transfer enough energy.
- This is analogous to choosing to briefly put your hand in a hot oven (low density) rather than in boiling water (high density).
Key Terms & Definitions
- Photosphere — the Sun's visible "surface," emitting most of its light.
- Chromosphere — a thin, colorful layer above the photosphere, made of hot jets called spicules.
- Spicule — a jet of hot gas shooting from the Sun's lower layers into the chromosphere.
- Corona — the Sun's outermost, extremely hot but thin "crown" layer.
- Density — how much material exists in a given space; affects heat transfer.
Action Items / Next Steps
- Review the diagram of the Sun’s layers on the class Discord.
- Prepare for questions about the properties and visibility of each solar layer.