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31 Cards in this Set
- Front
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How much energy can the Sun emit in one second? |
In one second the Sun emits enough energy to supply civilization’s power requirements for a million years. |
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How long has the Sun been keeping the Earth warm to sustain life? |
The Sun has been keeping the Earth warm enough to sustain life for at least 3.5 billion years. |
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What source of energy makes the Sun shine for only 31 million years? |
If the Sun shines, at its present rate, by converting gravitational potential energy into heat, it can last for only 31 million years. |
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What's the mean mass density of the Sun compared to that of the Earth? What does that indicate about the Sun's composition? |
The mean mass density of the Sun is just a quarter of the mean mass density of the Earth, indicating that the Sun is mainly composed of lighter material. |
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How old is the Sun? How old is the expanding Universe? |
The Sun is about 4.6 billion years old, but the expanding Universe is about 14 billion years old. |
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What's the temp, speed, location of solar material to support the Sun's overlying weight? What's the Sun's temperature at the visible solar disk? at the Sun's center? |
The solar material must become hotter, and move faster, at deeper depths in the Sun to support the overlying weight. At the visible solar disk the temperature is 5780 kelvin and at the Sun center it is 15.6 million kelvin. |
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What is the Sun mainly composed of? What does each hydrogen atom consist mostly of? |
The Sun is mainly composed of hydrogen. Each hydrogen atom consists mostly of empty space with a single proton in the nucleus and a single orbiting electron. |
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What is plasma? What happen to hydrogen atoms inside the Sun? |
Plasma: an ionized gas Hydrogen atoms are torn into pieces by collisions inside the Sun, so their nuclear protons and orbiting electrons are free to move about in plasma. |
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What is plasma? List four states of matter. Example of objects that are plasma. |
Plasma is the fourth state of matter, in addition to solid, liquid and gas. All stars and most of the Universe are plasma. |
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What's the density of material at greater depths in the Sun, compared to the Earth? What's the temperature down there? What's unexpected about protons and electrons at that depth? |
The material at greater depths in the Sun is compressed to larger densities, up to 13 times the density of solid lead at the center of the Sun. It is so hot down there that the protons and electrons behave like a gas in spite of the large density. |
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Where does the Sun's energy come from? |
The Sun’s energy comes from fusing protons together within the hot, dense core of the Sun, thereby converting mass into energy. |
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Where do two protons tunnel through? Why does the tunneling happen? How often does it happen? |
Two protons tunnel through the electrical barrier produced by the repulsion of their like charges. This tunneling is a quantum mechanical thing, made possible because protons do not have exact positions and energies, and the tunneling does not happen very often. |
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What is proton-proton chain? What does it do? |
The sequence of nuclear reactions in the Sun, called the proton-proton chain, converts four hydrogen nuclei, or four protons, into one helium nucleus. |
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What was Hans Bethe awarded the Nobel Prize in Physics in 1967 for? |
Hans Bethe was awarded the Nobel Prize in Physics in 1967 for his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production of stars like the Sun. |
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From the proton-proton chain, how is the mass of the helium nucleus compared to the four protons? Where does the mass loss go? What equation? |
A helium nucleus is just 0.7 percent less massive than the four protons that went into making it, but this mass loss, denoted by ?m, liberates an awesome amount of energy, E, given by Einstein’s celebrated equation E = ? m c2, where c is the velocity of light. |
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What happen when two protons fuse together? |
When two protons fuse together, they produce a positron, and an electron neutrino. Positron: the anti-particle of the electron |
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After being produced by the fusion of two protons, what happens to the positrons? the neutrinos? |
The anti-matter positrons immediately collide with the material electrons, disappearing in a puff of energetic gamma-ray radiation. The neutrinos pass effortlessly through both the Sun and the Earth. |
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What does the helium nucleus consist of? What happens to two of the four protons? |
The helium nucleus contains two neutrons and two protons, so two of the four protons that went into making a helium nucleus have to be neutralized. |
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When are two positrons and two neutrinos made? |
Two positrons and two neutrinos are made each time a single helium nucleus is synthesized. |
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What can the core of the Sun generate that no other part of the Sun can? |
Only the core of the Sun is hot enough and dense enough to generate energy by sustained nuclear fusion reactions; they cannot occur within other parts of the Sun. |
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How does the energy in the core of the Sun move to the solar disk? |
Energy generated in the core of the Sun slowly works its way out to the visible solar disk by radiation and convection. |
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More specifically, how is energy just outside the core transported? Where does it go? How long does it take? |
Just outside the core, energy is transported by radiation, taking 170,000 years to travel through the radiative zone and arrive at the bottom of the convective zone. |
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What is radiation blocked by? How long does energy take to travel through this blockage? |
Radiation is blocked by the convective zone, where energy is transported by currents of heated material, taking about 10 days to go from the bottom of the convective zone to its top. |
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What is the convective zone? |
The convective zone is capped by a thin layer of gas, the photosphere, where radiation is emitted as the sunlight we see. |
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What does the HD white-light images of the photosphere reveal? What is granulation? |
HD white-light images of the photosphere reveal the tops of gases rising out of the Sun by convection. Known as the granulation, they resemble Benard convection formed when a gas or liquid is heated from below, as with a pot of boiling water. |
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At any moment, how many granules can be seen in the photosphere? What is the photosphere? |
At any moment, about a million granules can be seen in the white light of the visible solar disk, the photosphere. They mark the tops of gases rising out of the Sun by convection, each granule lasting for about 15 minutes before another one replaces it. |
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What do velocity images of the photosphere revel? What is supergranulation? |
Velocity images of the photosphere reveal a large convective pattern, named the supergranulation, which moves mainly in the horizontal direction across the visible solar disk. The granules are superposed on this larger cellular supergranulation. |
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What is the Sun's luminosity in its early life compared to today? What can you assume about the Earth given the previous information? |
Our star began it life shining with only 70 percent of its present luminosity, slowing growing in luminous intensity as it aged. Assuming an unchanging terrestrial atmosphere, with the same composition and reflecting properties as today, the decreased solar luminosity would have caused the Earth’s global surface temperature to drop below the freezing point of water during its first 2.5 billion years. |
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But, what does geological evidence tell us about the Earth? What's the theory that explains it? |
Yet, there is clear geological evidence that the Earth was never this cold, and must have had a warm climate in its early history. The discrepancy between the Earth’s warm climatic record and an initially dimmer Sun has come to be known as the faint-young-Sun paradox. |
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How does the Sun's brightness change overtime? How do you know? What will happen in 3 billion years? |
The Sun is getting brighter as time goes on because there is a steady increase in the amount of helium in its core, resulting in hotter temperatures there. Sunlight will be hot enough in three billion years to boil the Earth’s oceans away. |
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What will happen to the Sun's and the solar system in seven billion years? |
In about seven billion years, the Sun will use up the hydrogen fuel in its core, and it will then balloon into a red-giant star, melting the Earth's surface and turning the frozen satellites of the outer planets into seas of liquid water. |
