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.