axial tilt: A planet moves in its orbit with its axis either straight up and down to its orbital plane or tipped to it. If the axis is straight up and down, it forms a 90 degree angle to the orbital plane. If it is tipped, then the planet is tilted from the perpendicular. The axial tilt is the amount the axis is tilted from the perpendicular. Axial tilt is measured in degrees. Some planets have almost no axial tilt. Jupiter and Mercury are tilted less than 5û from the perpendicular. Uranus and Pluto are tilted so far that they seem to be spinning on their sides.
