Make a gif of the Moon as seen from Earth for one lunar year, starting now - http://gfycat.com/SilverPositiveBluet

animated_moon.rb

require "usno/imagery"

require "open-uri"
require "RMagick"
include Magick

def animate(n,f)
  i=0
  time = Time.now

  1.upto(n).to_a.map {|t| time + (t * f * 60 * 60) }.map {|x| USNO::Imagery::Moon.new(time: x).call.data }.each do |url|
    i += 1
    open(i.to_s + "_image.png", 'wb') do |file|
      file << open(url).read
    end
  end

  ImageList.new(*1.upto(n).to_a.map(&:to_s).map {|x| "#{x}_image.png" }).write("animated_moon.gif")
end

# A "Lunar year" is about 355 days, we want 1 image per day
animate(355, 24)

Our moon

Mars seen from earth

Other options - https://github.com/rthbound/usno-imagery#usage