Ruby: Iterating through Constants

I'm just starting to use constants in Ruby.

I have

module Constants
  C1 = "foo"
  C2 = "bar"
end

I would like to do

Constants.each do |c|
  #do something with each one
end

but it says

undefined method ‘each’ for Constants::module

....

Is there a nice way of iterating through a list of constants?