Overview
This lecture takes a close look at the Sun's photosphere, explaining its appearance, granules, sunspots, and the relationship between sunspots, magnetic fields, and solar flares.
The Photosphere's Appearance
- The photosphere is the visible "surface" of the Sun, displaying yellows, oranges, and reds due to temperature differences.
- Yellow regions are hotter, while red regions are cooler areas of gas.
Granules and Convection
- Hot, yellow regions in the photosphere are called granules, formed by hot gas rising from the convective zone.
- As gas cools, it turns orange or red and sinks, creating a dynamic, constantly changing surface.
Sunspots: Formation and Properties
- Sunspots are dark spots on the photosphere that are cooler than surrounding areas.
- They appear dark only by contrast; they are still extremely bright.
- Sunspots are associated with strong magnetic fields and have magnetic north and south poles.
Magnetic Field and Differential Rotation
- The Sun's equator rotates faster than its poles because it is gaseous, not solid.
- Differential rotation causes the magnetic field to spiral and tangle over time.
- Tangled magnetic fields reach the surface, causing regions of gas to cool and form sunspots.
The Sunspot Cycle
- The number of sunspots on the Sun follows an 11-year cycle: increasing and then decreasing.
- As magnetic tangles increase, so do sunspots; eventually, the magnetic field snaps, and sunspots disappear as the field resets.
Solar Flares and their Relation to Sunspots
- Solar flares are eruptions of hot gas following magnetic field lines out of the Sun.
- More sunspots indicate increased solar flare activity, as both are caused by tangled magnetic fields.
- Solar flares can interfere with satellites but Earth's magnetic field protects us from harm.
Key Terms & Definitions
- Photosphere — the visible surface layer of the Sun.
- Granule — a small, hot, bright cell on the photosphere caused by convection.
- Sunspot — a dark, cooler spot on the photosphere linked to strong magnetic fields.
- Magnetic Field — invisible force field produced by moving electric charges.
- Differential Rotation — rotation at varying speeds at different latitudes.
- Solar Flare — a burst of hot gas and energy ejected from the Sun.
Action Items / Next Steps
- Review textbook sections on the photosphere, sunspots, and solar activity cycles.
- Be familiar with the causes and effects of sunspots and solar flares for upcoming assessments.