Question 1

The total time the Sun will spend converting hydrogen to helium in its core is:

Accepted Answer

The total time the Sun will spend converting hydrogen to helium in its core is about 10 billion years (10¹⁰ years). This is known as the main sequence lifetime of the Sun.

Question 2

What is a positron?

Accepted Answer

A positron is a particle with the same mass as an electron but with a positive charge instead of a negative charge. It is often referred to as the antiparticle of an electron.

Question 3

Who first postulated that hydrogen fusion reactions are responsible for generating the energy produced by the Sun?

Accepted Answer

Arthur Eddington was a British astrophysicist who, in 1920, was the first to suggest that the Sun's energy was produced by nuclear fusion of hydrogen nuclei into helium. This theory has since been confirmed by observations and experiments.

Question 4

In the thermonuclear process that is thought to heat the Sun,the nuclei of which chemical elements are converted to other nuclei to produce the requisite energy?

Accepted Answer

In the process known as nuclear fusion, hydrogen nuclei are combined to form helium nuclei, releasing a tremendous amount of energy in the process. This is the primary mechanism by which the Sun and other stars generate heat and light.

Question 5

At the present time,the energy of the Sun is generated:

Accepted Answer

The energy of the Sun is generated by fusion of hydrogen nuclei in its central core.

Question 6

How much matter is converted to energy in the Sun each second?

Accepted Answer

According to Einstein's famous equation E=mc^2, a small amount of matter can be converted into a large amount of energy. The Sun converts about 4 million tons of matter into energy every second, which is approximately 600 million tons per hour. Therefore, the best choice is D, 600 million tons, as it is the closest option to this estimate.

Question 7

The Sun's source of energy at the present time is thought to be:

Accepted Answer

The Sun's energy comes from nuclear fusion reactions that occur in the core, where hydrogen atoms combine to form helium. This process releases a tremendous amount of energy.

Question 8

The dominant energy source that powers the Sun at the present time is:

Accepted Answer

The dominant energy source that powers the Sun at the present time is thermonuclear fusion of hydrogen into helium in the core. This process releases vast amounts of energy in the form of light and heat. The fusion process occurs under intense pressure and temperature conditions, which are only found at the core of the Sun. As long as there is enough fuel, the fusion process will continue, providing a steady source of energy for billions of years.

Question 9

A positron is a:

Accepted Answer

A positron is a positively charged particle with the same mass as an electron but opposite charge.

Question 10

In terms of its total hydrogen-burning lifetime,the Sun is about:

Accepted Answer

The Sun is approximately 4.6 billion years old and is expected to have a total hydrogen-burning lifetime of about 10 billion years, making it roughly halfway through its life.

Question 11

What happens to the positrons produced by the nuclear reactions in the core of the Sun?

Accepted Answer

The positrons produced by nuclear reactions in the core of the Sun collide with electrons and form energy in a process called Annihilation. This process creates gamma rays, which can escape the Sun and potentially be detected by instruments on Earth. The other options are not accurate as neutrons are not present in the core of the Sun, and the production of helium requires a more complex process of fusion between multiple particles. The positrons are also not able to escape from the Sun due to the high density and pressure of the core.

Question 12

What process provides the power to maintain the Sun's radiative output?

Accepted Answer

The fusion of hydrogen into helium is the process that provides the power to maintain the Sun's radiative output. This process involves the conversion of mass into energy as four hydrogen nuclei combine to form a helium nucleus, releasing a large amount of energy in the process. This is known as nuclear fusion, and it is the source of the Sun's energy.

Question 13

The hydrogen fusion reaction is 4 ¹H → ⁴He + neutrinos + energy.What forms does this energy take?

Accepted Answer

The energy released in the hydrogen fusion reaction takes the form of kinetic energy associated with the motion of the helium, protons, and gamma-ray photons. It does not involve chemical energy or gravitational energy. While the protons do have kinetic energy before the reaction, this kinetic energy is not directly released as part of the reaction.

Question 14

How much longer can the Sun continue to generate energy by nuclear reactions in its core?

Accepted Answer

The Sun is currently in the middle of its main sequence phase which is expected to last about 10 billion years total. It is estimated that the Sun has already used up about half of its hydrogen fuel and will continue to generate energy through nuclear reactions in its core for another 5 billion years before it begins to evolve into a red giant.

Question 15

By how much does the mass of the Sun decrease each second because of the energy radiated from it (its luminosity)? (See the discussion in Discovery 9-1 in Comins,Discovering the Essential Universe,6th ed.)

Accepted Answer

The answer of By how much does the mass of...

Question 16

What is the MAIN source of the energy radiated by stars?

Accepted Answer

Stars primarily generate energy through nuclear fusion, where less stable nuclei, such as hydrogen, combine to form more stable nuclei, like helium, releasing energy in the process.

Question 17

Hydrogen "burning" by fusion reactions occurs only in the deep interior of the Sun (and other stars)because:

Accepted Answer

The core of the Sun (and other stars) is the only region where the temperature and density are both high enough to overcome the electrostatic repulsion between atomic nuclei, allowing nuclear fusion of hydrogen to occur.

Question 18

A hydrogen nucleus (a proton)has a charge of +1 and a helium nucleus has a charge of +2.Why,then,does it require four protons to form helium in the core of the Sun?

Accepted Answer

In the process of forming helium in the Sun's core, two of the protons undergo a transformation into neutrons through the process of beta decay. This is part of the proton-proton chain reaction, which ultimately results in the formation of a helium nucleus from four protons, with two of the protons turning into neutrons, thus creating a nucleus with two protons and two neutrons.

Question 19

From which fusion reaction does the Sun derive its power?

Accepted Answer

The fusion reaction that powers the Sun is the conversion of hydrogen-4 (⁴H) into helium-4 (He). This reaction is known as the proton-proton chain and involves a series of steps where multiple hydrogen nuclei combine to eventually create helium and release energy.

Question 20

When four protons collide to form helium,what fraction of the original mass of the protons is converted into energy?

Accepted Answer

In the fusion process where four protons form a helium nucleus, about 0.7% of the mass is converted into energy, which is approximately 3/4 of 1%.

Quiz 9: The Sun: Our Extraordinary Ordinary Star