<span>From the point of view of the astronaut, he travels between planets with a speed of 0.6c. His distance between the planets is less than the other bodies around him and so by applying Lorentz factor, we have 2*</span>√1-0.6² = 1.6 light hours. On the other hand, from the point of view of the other bodies, time for them is slower. For the bodies, they have to wait for about 1/0.6 = 1.67 light hours while for him it is 1/(0.8) = 1.25 light hours. The remaining distance for the astronaut would be 1.67 - 1.25 = 0.42 light hours. And then, light travels in all frames and so the astronaut will see that the flash from the second planet after 0.42 light hours and from the 1.25 light hours is, 1.25 - 0.42 = 0.83 light hours or 49.8 minutes.
Answer: 232 nm
Explanation: As it is well known the energy for the one dimentional box is given by:

where h is the Planck constant, m the electron mass and L the width of the box. n is the energy level
For n=3 we a energy equal :9.62 * 10^-19 J= 6.01 eV
For n=1 the energy is: 1.069 *10^-19 J=0.66 eV
The energy difference Is 5.35 eV so by using this relationship
λ=1240/Energy = 232 nm
A: decreases in specific heat capacity
It is a black hole. It is known that black holes are the are the most dense in space and that nothing can escape them.
Well, an electromagnetic wave can pass through a vacuum of space and examples of that is lasers. so the correct answer is A.Lasers.