#! /usr/bin/env python
"""
 relativity.py is program which calculates the time 
 in years that a spaceship takes to reach its destination
 as observed by someone on earth and as observed on the spaceship

 The program asks the user to input the restframe distance and 
 the spaceship speed. 

 Paul Eugenio 
 PHZ4151C
 Jan 15, 2019

### PROGRAM OUTPUT ###

hpc-login-24 511% relativity.py
 Enter distance in light years: 10
 Enter velocity as fraction of c: .99

 Time on Earth is 10.10 years
 Time on the spaceship is 1.42 years.

"""

# program header code
from __future__ import division, print_function
from math import sqrt


# main body of program
distance = float(raw_input("Enter distance in light years: "))

# v cannot be greater than or equal to c
velocity = 2
while velocity >= 1:
	velocity = float(raw_input("Enter velocity as fraction of c: "))
	if velocity >= 1:
		print("Velocity cannot be equal to or greater than the spped of light!")

gamma = 1/sqrt(1 - velocity**2)

# time on Earth = proper distance / velocity
print( "Time on Earth is {0:.2f} years".format(distance/velocity) )

# time on spaceship = contracted distance (x' = x/gamma) / velocity
print( "Time on the spaceship is {0:.2f} years.".format( (distance/gamma)/velocity) )