Bullet#angle

The angle property is the rotation of the Game Object in degrees from its original orientation.

Values from 0 to 180 represent clockwise rotation; values from 0 to -180 represent counterclockwise rotation.

Values outside this range are added to or subtracted from 360 to obtain a value within the range.
For example, the statement player.angle = 450 is the same as player.angle = 90.

If you wish to work in radians instead of degrees you can use the property rotation instead.
Working in radians is slightly faster as it doesn't have to perform any calculations.