Simplify the following text for a Grade 9 native English-speaking person.
Original: Calendars that are not solar calendars include the Islamic calendar , which is a purely lunar calendar and calendars synchronized to the synodic period of Venus or to the heliacal risings of stars .
Simplified: A solar calendar shows the earth 's position compared to the sun . There are tropical solar calendars , sidreal solar calendars , non-solar calendars ( like lunar - moon - calendars ) , and lunisolar calendars .