Let's make a planetary system!

• Practice creating custom classes
• Create an object which contains a collection of other objects
• Practice creating instance methods

• Create a SolarSystem class with an @planets instance variable.
• Create an initialize method which should take a collection of planet names and store them in an @planets instance variable.
• Create a method to add a planet to the list.
• Create a method which will return not print a list of the planets as a String in this style:

1.  Mercury
2.  Venus
3.  Earth
4.  Mars
5.  Jupiter
6.  Hoth

• Write code to test your SolarSystem
• Instead of Strings for planets, modify SolarSystem's initialize method to take a list of hashes where each planet is sent as a hash with at least 5 attributes.

• Give each planet a year_length attribute which is the length of time the planet takes to go around it's star.
• Give each planet a distance_from_the_sun attribute
• Write a program that asks for user input to query the planets:
  • First, ask the user to select a planet they'd like to learn about.
  • Present the user with a list of planets from which they can choose. Something like:
    • 1. Mercury, 2. Venus, 3. Earth, 4. Secret Earth, 5. Mars, 6. Jupiter, ... 13. Exit
  • Provide the user with well formatted information about the planet (diameter, mass, number of moons, primary export, etc.)
  • Then ask the user for another planet.

• Create a Planet class which will represent a planet.
  • Add an initialize method which takes several arguments and uses them to set the class' instance variables.
  • Create a method that returns the Planet's attributes in an easy to read fashion.
  • Create reader methods to give a user access to read the instance variables.
• Make your SolarSystem class take an array of Planets instead of hashes.
  • When printing the planet list or planet details, it should call the corresponding method in Planet.

• Create a method, outside any class, which creates a planet from user input.

• Create an interface where the user can interact with the solar system and be able to select a planet and view information about it.
• Allow your user to add their own planet.

• Ensure that the each planet has a @distance_from_the_sun attribute. Using this data, add a method to determine the distance from any other planet (assuming planets are in a straight line from the sun)
• Give your solar system an age (in earth years).
• Define a method that returns the local year of the planet based on it's rotation since the beginning of the solar system