16 (3) Flashcards
The outward flow of energy through (heat flow toward cold, core to the surface) a star robs it of its internal heat, and the star would cool down if that energy were not replaced. Similarly, a hot iron begins to cool as soon as it is unplugged from its source of electric energy. Therefore, a source of fresh energy must exist within each star. In the Sun’s case, we have seen that this energy source is the ongoing fusion of hydrogen to form helium.
R 2
There are three ways in which energy can be transferred from one place to another.
- conduction
- convection
- radiation
In ……………, atoms or molecules pass on their energy by colliding with others nearby.
conduction
This happens, for example, when the handle of a metal spoon heats up as you stir a cup of hot coffee.
In ……………., currents of warm material rise, carrying their energy with them to cooler layers.
convection
A good example is hot air rising from a fireplace.
In ……………, energetic photons move away from hot material and are absorbed by some material to which they convey some or all of their energy. Y
radiation
You can feel this when you put your hand close to the coils of an electric heater, allowing infrared photons to heat up your hand.
- ………… and ………….. are both important in the interiors of planets.
- In stars, which are much more transparent, …………. and ………… are important, whereas conduction can usually be ignored.
- Conduction / convection
- radiation / convection
In the Sun, convection turns out to be important in the central regions and near the …………….
surface
Radiation is not an efficient means of energy transport in stars because gases in stellar interiors are very …………….., that is, a photon does not go far (in the Sun, typically about 0.01 meter) before it is absorbed.
opaque
The absorbed energy is always reemitted, but it can be reemitted in any direction. A photon absorbed when traveling outward in a star has almost as good a chance of being radiated back toward the center of the star as toward its surface.
Energy is generated through fusion in the core of the Sun, which extends only about ………… of the way to the surface but contains about ………….. of the total ………… of the Sun.
one-quarter
one-third / mass
At the center, the temperature reaches a maximum of approximately 15 million K, and the density is nearly ………. times that of water.
150
The energy generated in the core is transported toward the surface by radiation until it reaches a point about ……….. of the distance from the center to the surface. At this point, convection begins, and energy is transported the rest of the way, primarily by rising columns of hot gas.
70%
astronomers have indeed devised two types of measurements that can be used to obtain information about the inner parts of the Sun.
- One technique involves the analysis of tiny changes in the ………… of small regions at the Sun’s surface.
- The other relies on the measurement of the ……….. ………. by the Sun.
- motion
- neutrinos emitted
Astronomers discovered that the Sun ………….—that is, it alternately expands and contracts—just as your chest expands and contracts as you breathe.
pulsates
This pulsation is very slight, but it can be detected by measuring the ………. ……….. of the solar surface—the speed with which it moves toward or away from us.
radial velocity
The typical velocity of one of the oscillating regions (Pulsating) on the Sun is only a few ………. ……… per ………., and it takes about ………. ………. to complete a full cycle from maximum to minimum velocity and back again.
The change in the size of the Sun measured at any given point is no more than a few ………….
hundred meters / second
5 minutes
kilometers
Pulsation measurements also show that the differential rotation that we see at the Sun’s surface, with the fastest rotation occurring at the equator, persists down through the ………… ………..
convection zone
