Brightest Star in the Sky is a very easy to get achievement, if you know how. This guide will help you get it. It can easily be done under 30 minutes.
You probably already got some gold stars, but the achievement wasnt awarded. Yeah, it isnt supposed to. The description is a bit wonky. To get the achievement, you should get a gold star rewarded before you get bronze or silver.

• Open scenario Pirate Battle from Captain Lockjaws Burried Treasures
  
• Build a place where customers can get drinks.
  
• Build a coaster (the game doesnt count coasters as rides, so this wont unlock bronze of silver).
  
• Put the game on 3x speed and wait.

These things you could try. They might speed up getting the achievement, but Im not sure.

• Get an ATM, so guest can stay in your park for longer. It isnt available from the start. You need to research First aid first, and then ATM research becomes available.
  
• Advertisement may speed up getting more guests in your park, if you have the money.