Monday, 28 February 2011

E3.1 - E3.8

continue from E 3.1:
The word parsec comes from one parallax second and it is abbreviated to pc.
The equation that had been mentioned:
'd' = the distance from earth to the star (parsec)
'p' = the parallax angle (arc second or seconds of arc)

E3.3 Explain why the method of Stellar parallax is limited to measuring stellar distances less than several hundred parsecs.
The parallax angle for stars that are at greater distances are too small to measure accurately. The parallax method can be used to measure Stellar distances that less than about 100 parsecs.  The limit on our ability to measure small angles therefore means  that the Stellar Parallax method can only be used to measure the distance of close stars.


The Apparent Magnitude (included in E 3.5)

E.3.6. Define Absolute magnitude
Absolute Magnitude (M) of a star -  the apparent magnitude (m) it would have if it were 10 pc from Earth. 
Stars would appear brighter if there were only 10 pc away but most stars are much further than 10 pc from Earth. Therefore, meaning that the absolute magnitude for most stars are more negative than their apparent magnitude. The absolute magnitude is ranged from -10 to +15.






Wednesday, 23 February 2011

E 2.7 Stella radiation

E.2.7 Explain how atomic spectra may be used to deduce chemical and physical data for stars
--> Stars that are approaching us will produce a blue-shifting and stars that are receding us will produce a red-shifting. The chemical and physical data for stars can be deduced through the chemical composition by analyzing the absorption spectrum and the luminosity by measuring the brightness and distance away.


Tuesday, 22 February 2011

Stella Radiation E.2.5 & E.2.6

E.2.5 Apply the Stefan-Boltzmann law to compare the luminosities of different stars


E.2.6 State Wien's (displacement) law and apply it to explain the connection between the colour and temperature of the stars. 

Wien's displacement law states that the peak wavelength of the emission of black body is inversely proportional to the temperature. This can be expressed as:
Note that if the peak wavemength is determined then the surface temperature of the star can be determined.
 Stars that has a high surface temperature will emit radiation over the full range of visible frequencies and thus will appear white. From Wien's law, this tells us that the lower surface temperatures will emit more light of a higher wavelength and thus will appear to be red.

Monday, 21 February 2011

E 2.1-2.4: Stella Radiatio

E 2.1: State that fusion is the main energy source of stars


E 2.2 Explain that, in a stable star (e.g. our sun), there is an equilibrium between radiation pressure and gravitational pressure:
Like any other stars, the sun is stable because there is an equilibrium between the outward pressure and the inward gravitational force.  The outward radiation is the heat generated during fusion and is calculated by E=mc2   and the inward force is the mass of the star.

 E 2.3 Define the luminosity of the star
Luminosity (L) is the total power radiated by the star or the energy emitted per unit time. It has a SI unit of watts. Luminosity depends on both the surface temperature and the radius or surface area of the star. If the radius of two stars are the same then the star with the highest temperature will have the greatest luminosity. If the temperature of two stars is the same then the one with the highest radius will have the greatest luminosity.

E 2.4. Define apparent brightness and state how it is measured
Apparent Brightness is the power incident on earth, perpendicular to unit area. It is measured using this equation:

Option E: Astrophysics 1.1- 1.5





3. Mnemonic:
My Very English Mum Just Sum Up Net Profit

5. Define:
-          Asteroid: a small rocky body that drifts around the solar system
-          Meteorite: an asteroid on a collision course with another planet
-          Comet: mixture of rock and ice in very elliptical orbits around the sun
-          Stellar Cluster: group of stars that are physically close to each other in space, created by the collapse of the same gas cloud
-          Constellation: patterns of stars that are not particularly close to each other
-          Light year: 1 light year is defined as the distance light travel in one year

6. Compare distances between stars and between galaxies


Describe motion of constellation over:
1.       1 night: The various constellation and stars are not the same as every night. This is because on any night, the stars constellations ‘rises’ about 4 minutes earlier than on the previous night. For example, the night sky at 10 pm on February 14 will be the same as at 9.54 p.m on February 15th
2.      1 year:

Photo of you and Orion 
(No stars last night)