Sidereal and solar time

Not only does the earth rotate arround her axis, but also arround the sun. When the sun is at her highest point in the sky, this is called twelve o'clock solar time. There is also a star that reaches it's highest point a that time. When the sun is at her highest point one month later, the earth as revolved thirty degrees arround the sun. The star that was at her hightest point one month aggo, has proceeded already thirty degrees. This is two hours later in sidereal time. Due to the rotation of the earth arround the sun a sidereal day is four minutes shorter than solar day.