Chapter 15

Summarize the evidence indicating that over several hundreds of years or more there have been variations in the level of the solar activity.

Counts of sunspots infer the overall magnetic field changes, which correlate with the level of the magnitude of the solar dynamo and hence solar activity. Astronomers have reliable data going back to 1750.

Describe how energy makes its way from the nuclear core of the Sun to the atmosphere. Include the name of each layer and how energy moves through the layer.

Energy is released as a result of nuclear reactions in the core of the Sun and travels upward (outward) in the form of light. It keeps doing that in the radiative layer, but as the temperature of the layer drops, the energy (wavelength) of the light drops as well. When the energy gets up to the convective layer, energy gets to the surface by moving the hot material of the Sun itself upward. The energy is released at the surface as light, cools the material, and the cooled material sinks back down again.

Compare and contrast the four different types of solar activity above the photosphere.

Plages are regions of higher density and temperature than the surrounding material in the chromosphere. Prominences are huge loops of the Sun's ionized but cool material that are gently pushed by magnetic force from the chromosphere into the corona. Flares are brief, violent explosions that are hot and release a lot of energy. Coronal mass ejections happen when a flare is so violent that the flare material exceeds the escape velocity of the Sun and is ejected out into the solar system. All of these are physically related to sunspots.

How does activity on the Sun affect human technology on Earth and in the rest of the solar system?

Solar activity can affect satellite orbits, communication satellites, and the local power grids. It can also impact our spacecraft throughout the solar system, especially orbiters or landers on surfaces without an atmosphere.

How does activity on the Sun affect natural phenomena on Earth?

Solar activity can affect the aurora, weather, and climate.

Why do sunspots look dark?

Sunspots appear dark because they are cooler than the surrounding area of the Sun.

What are the two sources of particles coming from the Sun that cause space weather? How are they different?

The Sun constantly throws off particles from the surface called the solar wind; this is constant and predictable over hundreds of years. The solar activity cycle can generate solar storms from coronal mass ejections, which are violent and hard to predict.

Describe the main differences between the composition of Earth and that of the Sun.

The Sun is composed primarily of hydrogen and helium, and its elements exist in the form of gases because of this hot temperature. Earth, in contrast, is made mostly of heavier elements and includes many in liquid and solid form.

What it the Zeeman effect and what does it tell us about the Sun?

The Zeeman effect is the splitting of spectral lines into several closely spaced lines due to the presence of a sunspot's magnetic field. The magnitude of the splitting tells us the strength of the local magnetic field on the Sun.

Which aspects of the Sun's activity cycle have a period of about 11 years? Which vary during intervals of about 22 years?

The number of sunspots goes from very few (maybe none) to about one hundred at one time (maximum) and back to very few (minimum) in cycles ranging from 9 to 14 years. During each cycle, the north or south magnetic pole of the sunspots leads. In the next cycle, the polarity reverses. So the overall magnetic activity of the Sun has an average cycle of 22 years.

Make a sketch of the Sun's atmosphere showing the locations of the photosphere, chromosphere, and corona. What is the approximate temperature of each of these regions

The order of the layers from the bottom up is: the photosphere (5800 K), the chromosphere (10,000 K), and the corona (1,000,000 K).

Explain how the theory of the Sun's dynamo results in an average 22-year solar activity cycle. Include the location and mechanism for the dynamo.

The solar dynamo is thought to be generated by ions in the lower part of the Sun's convective zone. Moving charged particles (in this case, the ions) generate a magnetic field. The fact that the Sun's fluid layers spin at different speeds at different latitudes then causes these magnetic fields to twist and distort, reversing about every 11 years.