Stargazers will often use a telescope to get closer to their desired subject, and returning to the same area can be a challenge - however recent innovations in telescope design have included motorised control with external devices through an "ST-4" port on the telescope.
This port can also be controlled with an Arduino and a small amount of external circuitry for PC-based control, and this has been demonstrated by Kévin Ferrare whose simple Arduino-based solution acts as a bridge between PC control software and the telescope. The degrees of movement can be controlled by an Arduino sketch or directly via the serial monitor and thus PC software. A demonstration is shown in the following video:
If you're looking to learn about Arduino development platform and how it interacts with external devices, you can't go past "Arduino Workshop - A Hands-On Introduction with 65 Projects” by John Boxall.
Arduino Workshop takes the reader from having zero knowledge about the Arduino platform, electronics and programming and leaves them with the know-how and instructions on everything from blinking an LED, to robotics, wireless data, cellular communications, motor control, sensors, Internet connected systems and more. For more information including a sample chapter and table of contents, visit the book page.