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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.

Categories within Stars


Postings: 6

The duration of a stars existence or usefulness.


Postings: 5

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


Postings: 5

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

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?

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


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

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:______________________________

Science of sunlight and stars

Here is what my team of 2 people need to do (A-F)and we don't know how to get it started. I only need help with Part A & D and then my partner and I will see how this is supposed to go. Please make Part A & D. a. The internal structure of the Sun and how astronomers learn about the Sun's interior (JUST EXPLAIN WHY & HOW) d


See attached file for full problem description. 1. Thoroughbred horse are among the fastest horses in the world and are used in famous racing events such as the Kentucky Derby. The mass of a thoroughbred is about 500 kg. If a horse with this mass is galloping with a momentum of 8.22*10^3 kg.m/s, what is its speed? 2. A pitch

Network Topologies

Outline the three general network topologies (bus, ring, and star). Describe the components, devices, and arrangement of components and devices involved in each topology, as well as some of the pros and cons of each configuration.

Calculating Escape Velocity

Determine the missing values for each different body (1 Newton=0.22 lb, 1 lb =4.54 N). Values should be carried out to 2 decimal places when it is not a whole number. http://hyperphysics.phy-astr.qsu.du/hbase/vesc.html#ves Use the following applet to calculate the escape velocity. Do not use commas when putting numbers into

Black Holes

Questions on the equation used to calculate the Schwarzschild radius of a black hole... See attached

Right ascension is discussed.

At what time will Galaxy -Cygnus A cross the celestial meridian (along north-south) direction on March 12 and 13 2005?

Optics: Resolving Power

1. The telescope on Mount Palomar has a diameter of 200 inches. Suppose a double star were 8.40 light-years away. Under ideal conditions, what must be the minimum separation of the two stars for their images to be resolved using light of wavelength 550 nm? (Unit: m) All answers must have three significant digits unless other


If a pair of helium nuclei are fused together, the result is, and why?

Light years

An astronomical unit of distance is the light-year, which is the distance light travels in one year. Compute this distance in meters. How many meters away is a star at a distance of 4 light-years from the earth?

Time journey

A spacecraft, traveling at a typical attainable speed of about 25,000 kilometers per hour, leaves Earth and travels toward the closest star system to Earth, the Alpha Centauri system. The time for journey would be about how many years?

Declination and right ascension

I'm stuck on this multiple choice question: Which of the following could be the equitorial co-ordinates of a star that rises to the south of east when viewed from 48 degrees north latitude, and 88 degrees west longitude? a declination 60, right ascension 13 hours b declination 30, right ascension 6 hours c declination -3

Star Measurements

A.) Briefly describe three ways that distances to stars can be measured. b.) Name an object, not man made , that emits light in pulsars similar to those from a pulsar. Any wavelegnth is okay. Could we detect these pulses if they came from Jupiter? From a nearby star? c.) Name a type of expansion (or expanding object) that