From the Super Mario Wiki
Mario Stargazer is a finding game on the Play Nintendo website.
The game starts with a title screen prompting the player to click anywhere to play. They must then click each spinning star to form a Super Star constellation. Afterwards, they must find nine more constellations featuring various Mario characters and items by moving their mouse to view the starry sky. The Super Star icon on the bottom screen will glow brighter as the player gets closer to finding a constellation; once they find one, they must click on the spinning stars to reveal each constellation. After the player finds every constellation, their time will appear, and they are then given the option to play again.