Simplify the following text for a Grade 10 native English-speaking person.
Original: In astronomy , axial tilt ( also called obliquity ) is the angle between an object 's rotational axis , and a line perpendicular to its orbital plane .
Simplified: In astronomy , axial tilt is the angle between a planet 's rotational axis at its north pole and a line perpendicular to the orbital plane of the Planet . It is also called axial inclination or obliquity .