Simplify the following text for a Grade 10 native English-speaking person.
Original: This occurs when the Pluto-Charon orbital plane is edge-on as seen from Earth , which only happens at two intervals in Pluto 's 248-year orbital period .
Simplified: This happens when the Pluto-Charon orbital plane is edge-on as seen from Earth , which only happens at twice in Pluto 's 248-year orbital period .