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Stars

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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Categories within Stars

Lifetime

Postings: 6

The duration of a stars existence or usefulness.

Pulsars

Postings: 5

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

Nebulae

Postings: 5

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

The proof of science

Why do we say that science does not prove anything? I do not understand this; the science I know proves everything. If you have any ideas I'd be very happy.

The Life Span of a Star

Please discuss the following: In general, is it possible to determine the life span of an individual star simply by noting its position on the H-R diagram?

Eratosthenes' Method

Drawing on Eratosthenes' method, if two observers are due north and south of each other and are separated by 400 km, what is the circumference of their spherical world if they see the same star on their meridian at altitudes of 23 degrees and 47 degrees respectively, and at the exact same time?

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?

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?

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

Which of the following statements are true about time dilation? 1. Time dilation suggests that an astronaut traveling to a distant star would actually age less than we would have measured at rest on Earth 2. Time dilation can be summarized by saying that a moving clock runs slower as compared to a clock at rest 3. Ti

Compute distance in meters, given 8.80 light years away

A star in our galaxy, Luyten, is 8.80 light-years away. That is, it takes 8.80 years for the light it emits to reach Earth. How far away is it in meters? Please solve and explain problem. If possible, please upload problem in pdf.

Schwarzschild radius

(a) Calculate the Schwarzschild radius of a supermassive black hole of mass 3.7 x 10^6 M., the estimated mass of the black hole at the galactic center. Give your answer in both kilometers and astronomical units. (b) What is the angular diameter of such a black hole as seen at a distance of 8 kpc, the distance from the Ear

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

The distance to Polaris, the North Star, is approximately 6.44 x 10^18 m. If Polaris were to burn out today, how many years would it take to see it disappear? (b) How long does it take sunlight to reach Earth? (c) How long does it take a microwave signal to travel from Earth to the Moon and back? (The distance from Earth to the

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.

Stars

1. In what order are the Bayer letters assigned to stars? 2. Is delta-Capricorni brighter than alpha-Capricorni? How do you know? 3. In what order are Flamsteed numbers assigned to stars? 4. How many nonstellar objects did Messier include in his catalog? 5. Why did Messier compile his list, and how were these obj

Five problems on velocity, acceleration, friction etc.

1)A coffee cup on the dashboard of a car slides forward on the dash when the driver decelerates from 42.7 km/hr to rest in 3.72s or less, but not if he decelerates in a longer time. What is the coefficient of static friction between the cup and the dash? 2)A chain consisting of five links, each of mass 0.180 kg, is lifted ve

Star's Temperature and Energy radiated by it

(a) A star's temperature is 6175 K. According to the Stefan-Boltzmann law, how much energy is radiated into space per second by each square meter of the star's surface ? 1..... J (b) If the star's radius is 605,000 km, what is the total power output of the star? 2 ...... W

Boltzman Law

The star Betelgeuse has a radius r=3.8 x 10^11m. Its surface temperature is 2800K (assume this is 1/2 of that of our Sun). Assuming Betelgeuse is a perfect emitter (e=1.0) what is its power output? What is the ratio of this power output to the power output of our Sun?

Cross section of a moving star

A star of radius R and mass M is moving with velocity v through a cloud of particles of density rho. If the particles that collide with the star are trapped by it, show that the mass of the star will increase at rate: dM/dt = Pi * rho * v * (R^2 +2GMR/v^2) Show how the cross sectional area compares with the geometric cros

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

Because of the presence of Jupiter, the Sun moves in a small orbit of radius 742,000 km with a period of 11.86 years. (a) Calculate the Sun's orbital speed in meters per second. (b) An astronomer on a hypothetical planet orbiting the star Vega, 25 light-years from the Sun, wants to use the astrometric method to search for plan

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

Please see the attached file. QUESTIONS: 1. What is the name of a star that is a good example of a: a. cool main sequence star: ___________________ d. red supergiant: _____________________ b. hot main sequence star: ___________________ e. blue supergiant: ____________________ c. red giant:______________________________

the minimum distance of separation of the two stars

The telescope on Mt Palomar has a diameter of 210 inches , A double star is 3 light years away. Under ideal conditions what is the minimum distance of seperation of the two stars for their images to be resolved in light of wavelength 500nm. Answer in meters please.