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    Sun Background

    Definition

    The Sun is the star at the center of the Solar System which the planets move around it in orbits.

    Basics

    The Sun is a star and the largest object in our solar system. The planets in our solar system move around the sun in orbits. Our sun can be seen in the sky in the day time. It is a large yellow ball. The sun is basically a very large ball of non-stop explosions. These explosions give off a lot of energy. Even though the sun is very far from the earth, we still feel this energy. The Sun is so bright that it can hurt to look at it and can damage your eyesight, so never stare at the sun and never use binoculars or a telescope to look at it. The Sun makes light, heat and the solar wind. Solar wind moves past the earth outside our atmosphere. It is made of small particles that fly away from the sun. The sun is the main source of energy for life on Earth.

    The Sun is at the middle of our solar system. Each planet travels in a more-or-less round orbit with the sun in the center. Each planet orbits at a different distance from the sun. The orbits of the planets are not perfect circles. They are closed-curves called ellipses. The planets closest to the Sun get more heat. Planets farther away are colder.

    Almost all life on our planet ultimately depends on the light energy that comes from our Sun. Plants use solar energy as food so they can grow. This process is called photosynthesis, the green in the leaves is the pigment.

    In the center of the Sun, in its core, great heat and pressure combine hydrogen gas into helium gas which produces large amounts of energy. This is called nuclear fusion.

    People can look at the Sun if they use special lenses that make it safe. When they do this, darker spots are sometimes seen on the surface of the Sun; these spots are called sunspots. The number of sunspots on the Sun gets bigger and then smaller in a cycle of about 11 years. The number affects the weather on Earth and can also affect electronics.

    Scientists think that the Sun started from a very large cloud of dust and small bits of ice 4.6 billion years ago. At the center of that huge cloud, some of the material started to build up into a ball. Once this ball got big enough, reactions inside it caused that ball to shine.

    At that point, the Sun blew away all the rest of the cloud from itself, and the planets formed from the rest of this cloud.

    At its core, or very center, hydrogen atoms are collided together to form helium. This process is called nuclear fusion. These helium atoms then travel from the core to the surface of the sun, called the photosphere, where they release their energy. Helium atoms can take thousands of years to reach the Sun's surface because other atoms get in their way.

    If the Sun is viewed through a very special telescope, dark areas known as sunspots can be seen. These areas are caused by the sun's magnetic field. The sunspots only look dark because the rest of the Sun is very bright.

    This is a cycle of 11 years, and every 11 years, there are more sunspots on the Sun than in the past or future years. Between these 11 years, sunspots may decrease in number. This cycle has been around since about the 1700s; before that was the Maunder Minimum, a few hundred years where there were very few sunspots. Astronomers don't know what caused this.

    Some space telescopes, like the ones that orbit the sun have seen huge arches that extend from the sun. These are called solar prominences. Solar prominences come in many different shapes and sizes; some of them are so large that the Earth could fit inside of them, and there are a few shaped like hands!

    Sometimes, the Sun "disappears" from the sky, and all that people see is a black but shining ball. This is because the Moon has moved right in front of the Sun and blocks almost all of its light. These happen almost every year, and very similar solar eclipses happen every 18 years, 11.3 days; a period called the Saros.

    Scientists called astrophysicists say our Sun is a main-sequence star in the middle of its life. In about another 4-5 billion years, they think it will get bigger and become a red giant star. The sun would be up to 250 times its current size, as big as 1.4 AU.

    Earth's fate is still a bit of a mystery. Previous calculations show that Earth could escape to a higher orbit. This due to the solar wind, which drops 30% of the sun's mass. But a newer study shows that Earth would possibly vanish itself. This would happen while the sun continues to get bigger due to the tidal forces. However, the sun will lose mass.

    Anyway, Earth's ocean and air would have long since worn out. This is even though the sun is still in its main sequence stage. After the Sun reaches a point where it can no longer get bigger, it will literally explode. But not like a supernova. Rather it will expand rapidly and lose its layers, forming a planetary nebula. Eventually the sun will shrink into a white dwarf. Then, over several hundred billion or even a trillion years, the sun would fade into a black dwarf.

    Topics of Interest

    The Sun is the star at the center of the Solar System. The Sun has a diameter of about 1,392,000 kilometres (865,000 mi) (about 109 Earths), and by itself accounts for about 99.86% of the Solar System's mass; the remainder consists of the planets (including Earth), asteroids, meteoroids, comets, and dust in orbit. About three-fourths of the Sun's mass consists of hydrogen, most of the rest is helium. Less than 2% consists of other elements, including iron, oxygen, carbon, neon, and others.

    The mean distance of the Sun from the Earth is approximately 149.6 million kilometers (1 AU), though this varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to the earth in about 8 minutes 19 seconds. The energy from this sunlight supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather. The enormous impact of the Sun on the Earth has been recognized since pre-historic times, and the Sun has been regarded by some cultures as a deity. An accurate scientific understanding of the Sun developed slowly, and as recently as the 19th century prominent scientists had little notion of the Sun's physical composition and source of energy. This understanding is still developing; there are a number of present-day anomalies in the Sun's behavior that remain unexplained.

    The core of the Sun is considered to extend from the center to about 0.2 solar radius. It is the hottest part of the Solar System. It has a density of up to 150,000 kg/m³ (150 times the density of liquid water) and a temperature of close to 15,000,000 kelvin (by contrast, the surface of the Sun is close to 6,000 kelvin). The core is made of hot, dense gas in the plasmic state.

    A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. The Latin root of the word corona means crown.

    Coronal loops form the basic structure of the lower corona and transition region of the Sun. These highly structured and elegant loops are a direct consequence of the twisted solar magnetic flux within the solar body. The population of coronal loops can be directly linked with the solar cycle, it is for this reason coronal loops are often found with sunspots at their footpoints. The upwelling magnetic flux pushes through the photosphere, exposing the cooler plasma below. The contrast between the photosphere and solar interior gives the impression of dark spots, or sunspots.

    Sunspots are temporary phenomena on the surface of the Sun (the photosphere) that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature. Although they are at temperatures of roughly 3,000–4,500 K, the contrast with the surrounding material at about 5,780 K leaves them clearly visible as dark spots, as the intensity of a heated black body (closely approximated by the photosphere) is a function of T (temperature) to the fourth power. If a sunspot were isolated from the surrounding photosphere it would be brighter than an electric arc. Sunspots expand and contract as they move across the surface of the sun and can be as large as 80,000 km (50,000 miles) in diameter, making the larger ones visible from Earth without the aid of a telescope.

    The formation and evolution of the Solar System is estimated to have begun 4.55 to 4.56 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the centre, forming the Sun, while the rest flattened into a protoplanetary disc out of which the planets, moons, asteroids, and other small Solar System bodies formed.

    Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.

    The solar neutrino problem was a major discrepancy between measurements of the numbers of neutrinos flowing through the Earth and theoretical models of the solar interior, lasting from the mid-1960s to about 2002. The discrepancy has since been resolved by new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics – specifically, neutrino oscillation. Essentially, as neutrinos have mass, they can change from the type that had been expected to be produced in the Sun's interior into two types that would not be caught by the detectors in use at the time.

    The faint young Sun paradox or problem describes the apparent contradiction between observations of liquid water early in the Earth's history and the astrophysical expectation that the Sun's output would be only 70% as intense during that epoch as it is during the modern epoch. The issue was raised by astronomers Carl Sagan and George Mullen in 1972.

    Humans have long recognized the Sun's role in supporting life on Earth (see Organism), and as a result many societies throughout history have paid homage to the Sun by giving it prominent roles in their religions and mythologies.

    Solar energy, radiant light and heat from the Sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available renewable energy on Earth. Only a minuscule fraction of the available solar energy is used.

    A Solar Deity (also Sun God(dess)) is a deity who represents the sun, or an aspect of it, usually by its perceived power and strength. Solar deities and sun worship can be found through-out most of recorded history in various forms. Hence, many beliefs have formed around this worship, such as the "missing sun" found in many cultures.

    Sun-Earth Day is a celebration established in 2000 by NASA and ESA. The purpose of the holiday is to popularize the knowledge about the Sun, and the way it influences life on the Earth.

    Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)

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