When I run the rake:db migrate command I get an error “Uninitialized constant CreateArticles”

Be sure that your file name and class name say the same thing(except the class name is camel cased).The contents of your migration file should look something like this, simplified them a bit too:

#20090106022023_create_articles.rb
class CreateArticles < ActiveRecord::Migration   
  def self.up
    create_table :articles do |t|
      t.belongs_to :user, :category
      t.string :title
      t.text :synopsis, :limit => 1000
      t.text :body, :limit => 20000
      t.boolean :published, :default => false
      t.datetime :published_at
      t.timestamps
    end
  end

  def self.down
    drop_table :articles
  end
end