Mercury (planet) three weeks, the Sun is almost stationary overhead, and is at its most brilliant because Mercury is at perihelion, its closest to the Sun. This prolonged exposure to the Sun at its brightest makes these two points the hottest places on Mercury. Conversely, there are two other points on the equator, 90 degrees of longitude apart from the first ones, where the Sun passes overhead only when the planet is at aphelion in alternate years, when the apparent motion of the Sun in Mercury's sky is relatively rapid. These points, which are the ones on the equator where the apparent
Sun and planet gear into circular motion using a 'planet', a cogwheel fixed at the end of the connecting rod (connected to the beam) of the engine. With the motion of the beam, this revolved around, and turned, the 'sun', a second rotating cog fixed to the drive shaft, thus generating rotary motion. An interesting feature of this arrangement, when compared to that of a simple crank, is that when both sun and planet have the same number of teeth, the drive shaft completes two revolutions for each double stroke of the beam instead of one. The planet gear is fixed to the connecting