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    A star is a large luminous sphere of plasma held together by gravity. The star that is most near the earth is the Sun. The Sun is the Earth’s main source of energy. Other stars are visible from the Earth in the night. Historically, the most prominent stars were grouped together into constellations and asterisms. Today extensive cataloged of stars have been assembled by astronomers. This provides standardized star designations.

    The formation of a star begins with gravitational instability within a molecular cloud. This is caused by regions of higher density that triggered by shack waves from a nearby supernovae, the collision of different molecular clouds or the collision of galaxies. Once the region reaches Jeans instability, it begins to collapse under its own gravitational force. When the cloud collapses, individual conglomerations of dense dust and gas form Bok globules. The density increases and the gravitational energy is converted into heat. When the cloud has reached a stable condition of hydrostatic equilibrium, a protostar forms at the core.

    Stars shine for a number of reasons. For a portion of their life stars shine due to thermonuclear fusion of hydrogen into helium in its core. It releases energy that traverses the star’s interior and radiated into outer space. Once the hydrogen is exhausted, all naturally occurring elements heavier than helium are created. This happens through stellar nucleosynthesis or by supernova nucleosynthesis. At the end of a star's life it contains a proportion of degenerate matter.

    Binary and multi-star systems are systems of two or more stars that are gravitationally bound. They generally move around each other in stable orbits. Their gravitational interactions can have a significant impact on their evolution. These systems of stars can be part of a larger gravitationally bound structure like a star cluster or galaxy.

    Historically, stars have played an important role to civilization throughout the world. Stars have been a part of religion, celestial navigation and orientation. Calendars and agricultural practices were also based on the motion of the sun against the background of the stars.

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    BrainMass Categories within Stars


    Solutions: 6

    The duration of a stars existence or usefulness.


    Solutions: 5

    A pulsar is a magnetized, rotating neutron star that emits a beam of electromagnetic radiation.


    Solutions: 5

    Nebulae is an interstellar cloud of dust, hydrogen, helium and other ionized gases.

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    The proof of science

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    The Life Span of a Star

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    Eratosthenes' Method

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    Physics: The Angular Speed of a Neutron Star

    Under some circumstances, a star can collapse into an extremely dense object made mostly of neutrons and called a neutron star. The density of a neutron star is roughly 10^14 times as great as that of ordinary solid matter. Suppose we represent the star as a uniform, solid, rigid sphere, both before and after the collapse. The s

    Space travel: How many years would it take to travel to a star?

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    Light-years away, distance traveled in light years.

    Part 1 A certain star is 73.3 light-years away. How many years would it take a spacecraft traveling 0.959c to reach that star from Earth, as measured by observers on Earth? Part 2 How many years would it take to reach that star from Earth, as measured by observers on the spacecraft? Part 3 What is the distance (

    Truth Statements on Time Dilation

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    Compute distance in meters, given 8.80 light years away

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    North Star, frequency of light, radio waves, underwater sun

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    Brightness of a Supernova

    Suppose that the brightness of a star becoming a supernova increases by 20 magnitudes. Show that this corresponds to an increase of 10^8 in luminosity.


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    Five problems on velocity, acceleration, friction etc.

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    Star's Temperature and Energy radiated by it

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    Boltzman Law

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    Cross section of a moving star

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    Dobble star system: Centripetal Force

    The two components of a double star are observed to move in circles of radii r1 and r2. What is the ratio of their masses? Hint: write down their accelerations in terms of the angular velocity of rotation, omega.

    Orbital Speed/Angular Diameter

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    What is the name of a star that is a good example of a

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    the minimum distance of separation of the two stars

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