Astronomy Ch. 16 – The Sun

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The light we see from the Sun comes from which layer?


Why couldn’t you stand on the Sun’s surface?

The Sun doesn’t have a solid surface.

The area in the Sun’s atmosphere located above the chromosphere (1500-10,000 km) where the temperature rises dramatically is called the

transition zone.

The luminosity of the Sun is a measure of

the total energy emitted by the Sun in all directions.

Hydrostatic equilibrium in our Sun is the balance between

gravitation and pressure.

When we glimpse the chromosphere at the start and end of totality, its color is

red, due to ionized hydrogen at lower pressure.

The percentage (by number of atoms) of the Sun that is Hydrogen is about


How long does the sunspot cycle last, on average?

about 11 years

The most striking example of solar variability as the

Maunder Minimum from 1645-1715.

The numbers of sunspots and their activity peak about every:

eleven years.

The critical temperature the core must reach for a star to shine by fusion is

10 million K.

The primary source of the Sun’s energy is

the strong force fusing hydrogen into helium.

What natural barrier tried to prevent two protons from combining?

electromagnetic repulsion

The critical temperature to initiate the proton-proton cycle in the cores of stars is:

10 million K.

Which is the net result of the proton-proton chain?

4 protons = 1 helium 4 + 2 neutrinos + gamma rays

The speed of light is 3.00 × 10⁸m/s. If 2.00 kg of mass is converted to energy, how much energy will be produced?

1.80 × 10¹⁷ J

The temperature of the layer of gas that produces the visible light of the Sun is:

5,800 K

How many planet Earths could fit inside the Sun?

a little over a million

The density of the Sun is most similar to which object?


About what percent of the incoming energy from the Sun’ reaches Earth’s surface?


The solar constant is a measure of

the energy received by the Sun at the location of Earth.

From inside out, which is in the correct order for the structure of the Sun?

radiative zone, convective zone, chromosphere

By what mechanism does solar energy reach the Sun’s photosphere from the layer just underneath it?


The vibrations of the Sun reveal information about

the interior structure of the Sun.

What two energy transport mechanisms, in order from outside the core to the surface, is found in the Sun?

radiative diffusion, convection

What is the size of a typical granule or convection cell seen in the photosphere?

1,000 km

The pattern of rising hot gas cells all over the photosphere is called:


The outward pressure of hot gas in the Sun

is balanced by the inward gravitational pressure.

When the chromosphere can be seen during a solar eclipse, it appears:


From where does most of the solar wind flow?

coronal holes

What is it about the Sun’s corona that astronomers don’t understand?

The corona is much hotter than layers of the Sun that are closer to the solar interior.

The percentage (by mass) of the Sun that is Hydrogen is about


The percentage (by mass) of the Sun that is Helium is about


A loop of gas following the magnetic field lines between sunspots’ poles is

a prominence.

Visible sunspots lie in the

granulation in the photosphere.

As the Sun rotates, an individual sunspot can be tracked across its face. From eastern to western limb, this takes about

two weeks.


come in pairs, representing the north and south magnetic fields.

Sunspots are dark splotches on the Sun. Which statement is true?

They are extremely hot, but cooler than the surrounding areas of the Sun.

How would sunspots appear if you could magically remove them from the Sun?

They would shine bright orange in color, like Arcturus.

While observing the Sun, you note a large number of sunspots. What can you conclude?

There are likely to be an above average number of flares and prominences.

Loops of glowing hydrogen seen hanging over the solar limb during totality are:


During a period of high solar activity, the corona

is more irregular.

The solar winds blow outward from

coronal holes.

Which of these are not associated with the active Sun?


Suppose a large flare is detected optically. How long until radio interference arrives?


Which of the following is NOT a property of neutrinos?

cannot interact at all with normal matter

In the proton-proton cycle, the helium atom and neutrino have less mass than the original hydrogen. What happens to the "lost" mass?

It is converted to energy.

In the proton-proton cycle, the positron is

an anti-electron.

(SA) Explain what the granulation of the solar surface is related to.

The surface of the Sun is highly mottled or granulated. Each granule is about 1,000 km across. The granulation is produced by the convection (boiling) of the Sun’s gases. Each granule is the top of a convection cell that is welling up.

(SA) Describe the transport of energy, from the deep interior of the Sun, to when it finally reaches the Earth. Include the various methods of transport.

Energy is produced in the core. It enters the radiative zone, where it moves as radiation. As it gets further out from the center, the gas gets less ionized and so more opaque to radiation. In this region the energy moves by convection, with hot gas physically rising through the Sun. When it reaches the surface, or photosphere, the low density makes the Sun transparent, and the energy escapes as light.

(SA) If the corona is so hot, why must we wait for a total solar eclipse to glimpse it?

It is so hot that almost all the energy it gives off, by Wien’s Law, is not going to be in the visible, but the X-ray portion of the spectrum. Also, it is very low density, so there are far more atoms at 5,800 K giving off a lot of visible light than the few out in the corona.

(SA) In the proton-proton cycle, two positrons are produced. What are they similar to, and how are the different? What happens to them?

Positrons are the antiparticle to the electron. They are like the electron in mass but positive in charge. When positrons inevitably meet electrons, both particle and antiparticle are annihilated and energy is given off.

(SA) Why is studying the neutrino so vital to understanding the solar interior?

Alone of all the products of the proton-proton cycle, only the neutrino can easily escape the Sun and reach the Earth at almost the speed of light. The flux of neutrinos should be in agreement with the observed solar constant, if our model of solar energy production is correct.

(SA) A solar flare creates a radio disturbance on Earth a few minutes after going off and again several days later. Explain.

A flare will give off intense X-rays and ultraviolet light, which travels to Earth in about 8 minutes. But also given off is an intense burst of high energy particles which travel to the Earth at speeds much less than the speed of light. They can take several days to reach the Earth. Both forms of radiation create radio disturbances when they reach the Earth.

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