Chp 3. 1) a) When Venus is fully illuminated as seen from Earth, it cannot be between the Earth and the Sun at that time , but must be beyond the Sun. When Venue is seen to be in crescent phase, it must be between the Earth and the Sun (or we wouldn’t be seeing the " dark side"). The "closer" and "farther" size indicators just confirm what plain from degree of illumination.

b) In the Copernican system, as Venus orbits the Sun it will sometimes be on the side of its orbit closer to Earth, and at other times it will be far side of its orbit, therefore on the far side of the Sun from Earth. This is not the case in the Ptolemaic system, in which Venus would always stay between the Earth and the Sun.

2) Venus is the closest to the Earth (0.3 AU from Earth) while other planets are far than this.(values given behind the book for reference)

8) a) As it is given that the orbit is circular, so the distance traveled would be the circumference of the circle i.e. 2p R Kilometers .Now velocity is given by the following :

V = Distance covered / Time = 2p
R/ T = 2*1.5*10^{8}/10^{7} = 30 Km/sec

b) To reach escape velocity from the Sun, the object at Earth's orbital distance would need

V = 1.4*30 km/sec = 42 km/sec

Chp 5. 1) The formula for calculating number of years is given by:

F = (1/2)^{N} and F= 1/4 (given)

[1/4 = (1/2)^{2}] hence N = 2

so for F= 1/4 , two half-lives have gone by since the mineral formed, two billion years.

Chp 6. 3) Venus has a hotter surface. Mercury has no atmosphere, and no internal heat, so its temperature is determined by the equilibrium between the solar energy coming in and the heat the planet radiates out. In Venus's case, the atmosphere acts as a blanket ( the "green house effect") to increase the surface temperature dramatically beyond the value you might expect from simple equilibrium arguments.