Astronomy Ch. 10

What do astronomers mean by a "model of the Sun"?

A model of the Sun is the set of mathematical equations that govern the behavior of matter and energy and their solution using the parameters relevant to the Sun.

What is a neutrino, and why are astronomers so interested in detecting neutrinos from the Sun?

A neutrino is an almost massless particle that is produces by hydrogen fusion. Neutrinos have the ability to penetrate vast amounts of matter. When astronomers detect neutrinos from the Sun they are coming directly from the core and are the only direct core observations possible.

Give an everyday example of hydrostatic equilibrium not presented in the book.

An inflated balloon will expand until the stretched rubber exerts an inward pressure that balances the gas pressure on the inside.

prominence

Flamelike protrusion seen near the limb of the Sun and extending into the solar corona. The side view of a filament.

What is hydrogen fusion? This process is sometimes called "hydrogen fusing." How is hydrogen burning fundamentally unlike the burning of a log a in fireplace?

Hydrogen fusion means the process of combining four hydrogen nuclei to form one helium nucleus. This is incorrectly referred to as hydrogen burning because hydrogen is the fuel. The burning of a log is a chemical reaction, whereas hydrogen fusion is a nuclear reaction.

Name and describe seven features of the active Sun. Which two are the same, seen from different angles?

Seven features of the active Sun are sunspots, plages, flares, filaments, prominences, coronal holes, and coronal mass ejections. Filaments and prominences are the same feature seen from different angles. Coronal mass ejections and flares have a direct impact on the Earth. They cause aurora and radio interference.

Describe the dangers in attempting to observe the Sun. How have astronomers learned to circumvent these hazards?

The danger in observing the Sun is from ultraviolet light that can cause permanent eye damage. Astronomers have learned how to filter out the ultraviolet.

Describe the features of the Sun's atmosphere that are always present.

The features of the Sun that are always present are the granulation of the photosphere, the spicules in the chromosphere, and the faint corona. These features are a result of the normal energy transfer in the Sun.

Describe the Sun's interior, including the main physical processes that occur at various levels within the Sun.

The hottest and densest part of the Sun is the core when hydrogen fusion is occurring. Surrounding the core is the radiative zone where energy from the core is moving upward by radiative transport. Surrounding the radiative zone is the convective zone where huge updrafts of matter carry heat to the surface.

How do astronomers detect the presence of a magnetic field in hot gases, such as the field in the solar photosphere?

The magnetic field causes some spectral lines to split by the Zeeman effect. The splitting is observable and indicates the presence of the magnetic field.

Describe the three main layers of the solar atmosphere and how you would best observe them.

The main layers are the photosphere, chromosphere, and corona. The photosphere is the normally visible surface of the Sun and can be observed with visible light. The chromosphere and corona are best observed during total eclipses or artificial eclipses produced by coronagraphs. The chromosphere can also be observed at particular wavelengths at which the chromosphere is bright by filtering out the other wavelengths. In addition to these, the corona can be observed at X-ray wavelengths.

Why is the solar cycle said to have a period of 22 years, even though the sunspot cycle is only 11 years long?

The solar cycle refers to the magnetic cycle, which lasts 22 years. During one solar cycle, there are two cycles of sunspot numbers.

Describe the three main layers of the Sun's interior.

The three main layers are the core where the energy is generated, the radiative zone where energy is transported upward carried by photons, and the convective zone where convection carries the energy to the surface.

Why do thermonuclear reactions in the Sun take place only in its core?

Thermonuclear reactions require a temperature of 10 million K. Only the Sun's core has this temperature.

Give some everyday examples of heat transfer by convection and radiative transport.

Warm air in a room rise by convection. The radiant heat from a fireplace warms the occupants of the room.

solar cycle

a 22-year cycle during which the Sun's magnetic field reverses its polarity twice.

hydrostatic equilibrium

a balance between the wight of a layer in a star and the pressure that supports it

plages

a bright spot on the Sun believed to be associated with an emerging magnetic field

filament

a dark curve seen above the Sun's photosphere that is the top view of a solar prominence

coronal hole

a dark region of the Sun's inner corona as seen at X-ray wavelengths

plasma

a hot, ionized gas

super-granule

a large convective cell in the Sun's chromosphere containing many granules

convective zone

a layer in a star where energy is transported outward by means of convection; also known as the convective envelope or convective zone

spicule

a narrow jet of rising gas in the solar chromosphere

thermonuclear fusion

a reaction in which the nuclei of atoms are fused together at a high temperature

radiative zone

a region inside a star where energy is transported outward by the movement of photons through a gas from a hot location to a cooler one

solar model

a set of equations that describe the internal structure and energy generation of the Sun

Zeeman effect

a splitting of spectral lines in the presence of a magnetic field

neutrino

a subatomic particle, with no electric charge and little mass, that is important in many nuclear reactions and in supernovae

sunspot

a temporary cool region in the solar photosphere created by protruding magnetic fields

magnetic dynamo

a theory that explains phenomena of the solar cycle as a result of periodic winding and unwinding of the Sun's magnetic field in the solar atmosphere

solar flare

a violent eruption on the Sun's surface

positron

an electron with a positive rather than negative electric charge; an anti electron

solar wind

an outward flow of particles (mostly electrons and protons) from the Sun

coronal mass ejection

large volumes of high-energy gas released from the Sun's corona

granule

lightly colored convection features about 1000 km in diameter seen constantly in the solar photosphere

Cerenkov radiation

radiation produced by particles traveling through a substance faster than light can

transition zone

region between the Sun's chromosphere and corona where the temperature skyrockets to about 1 million K

limb (of the Sun)

the apparent edge of the Sun as seen in the sky

core (of the Sun)

the central quarter of the Sun's radius, in which hydrogen is fused into helium, releasing the energy that enables the Sun to shine

chromosphere

the layer in the solar atmosphere between the photosphere and the corona

corona

the outermost layer of the Sun's atmosphere

limb darkening

the phenomenon whereby the Sun is darker near its limb than near the center of its disk

photosphere

the region in the solar atmosphere from which most of the visible light escapes into space

differential rotation

the rotation of a nonrigid object in which parts at different latitudes or different radial distances move at different speeds

helio-seismology

the study of vibrations of the solar surface

hydrogen fusion

the thermonuclear fusion of hydrogen to produce helium

sunspot maximum

the time during the solar cycle when the number of sunspots is greatest

sunspot minimum

the time during the solar cycle when the number of sunspots is minimum

solar luminosity

the total energy emitted by the Sun each second