Evidence of the Earth's rotation (from west to east) is seen with the deflection of objects moving in north-south direction caused by the differences in the linear speed of the rotation at different latitudes. All parts of the Earth take 23 hours 56 minutes to turn once, but the higher latitudes are closer to the Earth's rotation axis, so they do not need to rotate as fast as regions nearer the equator. A moving object's west-east speed will stay at the original value it had at the start of its motion (unless some force changes it). If the object is also changing latitudes, then its west-east speed will be different than that for the part of the Earth it is over. Therefore, moving objects appear to be deflected to the right in the northern hemisphere and to the left in the southern hemisphere. This is called the
coriolis effect after
Gustave-Gaspard Coriolis (lived 1792--1843 C.E.) who deduced the effect in 1835 to explain why cannonballs shot long distances kept missing their target if the cannon was aimed directly at its target. See
energy flow section for applications (and illustrations) of the coriolis effect to planet atmospheres.