From the Core to the Corona – a Journey through the Sun

A Model for most stars in the Universe

The Sun’s Core The energy production site Temperature = about 15 million degrees Kelvin Energy is generated in the core by nuclear fusion Nuclear fusion is due to great pressures causing protons from hydrogen to slam into one another creating helium The core accounts for 40% of the sun’s mass, while only occupying 10% of the total volume. In other words, the core is really really really dense…

The Radiation Zone Upward and Outward! Energy is transported out of the core of the Sun Much less dense than core Energy has a harder time passing through it. Energy is free moving It can take hundreds of thousands to millions of years of years for energy (light) to get out of the radiation zone

The Radiation Zone Towards the edge of the radiation zone, the temperature cools enough that the energy from the core cannot move freely. Instead it gets absorbed by the plasma (hot gas of the Sun) and starts a process known as convection.

Convection Zone The outermost layer of the Sun’s interior layers Brings light and energy to the surface of the Sun through convection currents Temperature range from 2 million to 6,000 degrees Kelvin.

The Photosphere The lower atmosphere of the Sun This is where the energy finally is released, mostly as thermal energy, but also as the visible light we see. The coolest region of the Sun (6000 Kelvin)

Granulation The Sun’s photosphere looks like rice grains. Large convection cells cause this granulation, since each cell has a column of hot gas rising and cool gas descending. Granules the size of Earth and larger constantly evolve and change in a churning kind of motion.

Chromosphere The region immediately above the photosphere 2000-3000 km thick Glows faintly relative to the photosphere Can only be seen easily in a total solar eclipse Temperature is about 20,000 degrees Kelvin Primary source of UV radiation

The Solar Corona The corona is extended outer atmosphere of the Sun 1 million times less bright than the photosphere Can only be seen during a total solar eclipse or by using a tool called a coronagraph, which artificially blocks out the disk of the Sun.

6,000 K 1,000,000 K The Sun’s surface temperature is about 6,000 degrees K The temperature in the corona reaches about 1 million degrees K

The Solar Wind A constant stream of particles flows from the Sun’s corona, with a temperature of about a million degrees and with a velocity of about 450 kilometers per second. The solar wind reaches out beyond Pluto's orbit (about 5900 million kilometers). This wind helps shape the magneto- spheres of planets and blows off the material that forms the tails of comets.

The Path of Sunspots Because of differential rotation, the magnetic field of the Sun is very much different from that of the Earth. Sunspots often occur in pairs along these lines.

The Path of Sunspots Strong magnetic forces prevent the mixing of cooler and warmer areas, which creates the appearance of sunspots. This is also the path for solar prominences

The Path of Sunspots Notice how the prominence seems to loop similar to the magnetic field

The Path of Sunspots Sunspot Cycle – sunspot maximum occurs every 11 years. Last sunspot maximum was in 2001.

Solar Prominences A fairly common occurrence They are eruptions caused by magnetic forces. Cooler gases above the photosphere can often be seen flowing along magnetic field lines.

Large Solar Prominences This is the largest prominence observed. This huge prominence is 100,000 kilometers above the Sun. 28 Earths high

Some Neat Little Ditties. How do we know the temperature of the Sun? Wiens’s Law = Hotter bodies radiate more energy at shorter wavelengths. Each wavelength has its own color So, temperature is related to surface color of the star and hotter stars are brighter if seen from the same distance How do scientists know that the Sun has a core? The only thing that provides enough energy to heat a star for billions of years is nuclear fusion. How long until the Sun explodes? About 5,000,000,000 years. How do we know the composition of the Sun? The solar wind and spectra analysis. Sunspot Cycle sunspot maximum occurs every 11 years. Last sunspot maximum was in 2001. One second of its Energy = total energy produced in the US for 90 years Is one of about 2 billion medium sized stars in out galaxy If you drove a car at 100 miles per hour to the Sun, how many years would it take to get there? 5, 50 or 100. About 100 years