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The Photosphere

Delve into the Sun's layers from the Photosphere to Core in this educational guide, exploring phenomena like Sunspots, Flares, and more.

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The Photosphere

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  1. The Photosphere • The point at which gas is thick enough that we can’t see through it • This is a little shallower towards the edge • Limb darkening Here we see shallow and cool Here we see deep and hot

  2. Granulation • The Sun’s surface is not uniformly bright • Hot regions of upwelling gas • Cooler regions of falling gas • Convection near the surface https://www.youtube.com/watch?v=W_Scoj4HqCQ

  3. Granulation • Granulation changes over time

  4. Granulation • Circulation of gases in outer layer • Hot plasma rising, cool plasma falling – convection • Underneath, evidence of circulation on a larger scale • Supergranules larger than the Earth Earth

  5. Chromosphere • A cooler layer just outside the photosphere • Light from photosphere lines absorbed from this layer • Bright line spectrum • Visible during eclipses • Red color from spectral line of hydrogen

  6. Spicules • Bright small jets that reach from the photosphere up through the chromosphere • Last about 5 minutes • Cause not understood • Thousands on the Sun at any given time

  7. Corona: Temperature • Thin, extremely hot region • Visible during eclipses • High temperature not well understood • Heated by magnetic fields • Like a whip • Low density – has little total heat Q. 63: Coronal Spectrum

  8. Sunspots • Relatively cool regions on a brighter, hotter background • Large magnetic fields What causes them: • Magnetic field sticks out • Plasma can’t flow horizontally • Prevents convection from working • Hot gas can’t rise • Temperature cooler

  9. Sunspots - Structure Penumbra Umbra

  10. Sunspots Often Come in Groups • Pairs are common • North with south • Larger groups are not uncommon

  11. The Solar Cycle • The number of sunspots changes over time • Approximately an eleven year cycle: Butterfly diagram • Sunspots first appear far from the equator • Over time, they become more numerous, and move towards the equator • Then they all disappear • Each cycle of eleven years, the Sun’s north and south magnetic poles switch Q. 64: Sunspot Cycles

  12. The Solar Cycle • Sun’s North/South magnetic pole reverses each cycle • Not all cycles are created equal! • 1650-1700, very low level, “Maunder Minimum” • Corresponded to “Little Ice Age” in Europe • Level of sunspots/magnetic activityaffects all othersolar activity

  13. The Solar Cycle

  14. Flares Explosive release of magnetic energy on surface of the Sun • Typically reach through photosphere, chromosphere, to corona • Burst of energy, especially X-rays • Can cause coronal mass ejections

  15. Prominences Loops of magnetic fields sticking high above the Sun’s surface

  16. Prominences

  17. Prominences

  18. Prominences • Chargedparticlesfollowingmagnetic linesfrom insidethe Sun • https://www.youtube.com/watch?v=EATDvxnLXyc

  19. Coronal Mass Ejections • Flares can expel gas at high velocities from the Sun • Similarly, prominences can become “disconnected” • High temperature gas expelled at high velocity • Up to half the speed of light • These events are called coronal mass ejections • They can cause satellite malfunction and communication disruptions on Earth • They pose a major danger to astronauts beyond the Earth’s magnetosphere

  20. Coronal Holes • Most gas in the corona is trapped by the Sun’s magnetic fields • “Coronal holes” allow some to escape to space • This creates the solar wind

  21. The Solar Wind • Particles flowing outward from Sun travel to Earth and beyond • Contains hydrogen, helium, etc. • Magnetic fields Earth funnel them to Earth’s magnetic poles • Causes the Aurora Borealis and Aurora Australis

  22. Helioseismology • Vibrations of the Sun tell us some things about its interior • Much like earthquakes for the Earth • Need to be matched with detailed computer models of interior of Sun • Together with our knowledge of its composition and total power output

  23. Interior Structure of the Sun There are three layers to the interior of the Sun • The Core: • Where the energy is generated • The Radiative zone • Heat is transported by radiation • The Convective zone • Heat is transported by circulation

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