Astrophysics E.2 - E.4

E.2.1

Fusion is the main energy source of stars. For fusion to take place high pressures and high temperatures are needed.As temperature is proportional to energy, this means that high temperatures are needed to gain high energies to overcome the electrostatic repulsion between two atoms. High pressures are needed to bring the atoms close enough together for them to bond.

E.2.2

A stable star is essentially a ball of hot gases. As temperature increases gases expand, which leads us to believe that a star  should be forever expanding however all particles mass have their own gravitational attraction. This means that once a star gets to a certain size the attraction of gravity between particles becomes equal and opposite to that of the radiation pressure. This is when the star ceases to continue growing in size.

E.2.3
Define luminosity
The total power radiated by a star is called its luminosity

E 2.4 
The brightness of a star when brought to a distance of 10 parsecs away from the observer is called the apparent brightness.

E 2.5 
The Stefan Boltzmann law defines that luminosity is proportional to the Temperature^4
to compare the luminosities of different stars you must use the following equation:

E 2.6

Wein's law states that lambder max (the most commonly emitted wavelength - the most intense wavelength) is inversely proportional to temperature. 

This means that surface temperature of a star can be determined by the maximum wavelength of the light emitted. 

The graph above illustrates wavelength against intensity, lambder max is the most intense wavelength emitted (all wavelengths are emitted however we are looking for the most commonly emitted wavelength). The most intense wavelength defines the temperature of the star. 

The colours on the graph illustrate what colour the star will be according to its lambder max. 

This is Wein's Law.

E 3.1 A parsec is defined as the distance between the earth and a distance stellar object when the angle subtended on us by the distant object is equal to two arc seconds over a time period of a year. 

E 3.2 

Dont understand, but basically d=1/p where d is the distance between the star and the earth and p is the parallax angle in arc seconds. 

E 3.3

The parallax method only works for stellar objects that are roughly less than 300 parsecs away from the observer. This is because past this distance the angle tends to closely to zero for us to measure accurately. 

E 3.4 
d=1/p

E 3.5

The apparent magnitude scale is a comparative scale of apparent brightness of different stellar object of which the lower the value the brighter the object. If the magnitude is over the value of 6 - the naked eye limit - the object is not visible without a telescopic lens. 

The apparent magnitude is dependent on the luminosity and the distance of the star. 

E 3.6

The absolute magnitude is the brightness of a star at a distance of 10 parsecs. 

E 3.7 & 3.8 

Solve questions, when it's not quarter to 12 and when im not about to collapse from physical and mental stress.