f = PN/120 where f is frequency of power supply, P is number of poles in the machine and N = speed in rpm. So, Synchronous speed N = 120f/P. Thus for 50 Hz supply, 2 pole machine; synchronous speed = 3000rpm. ETRICAL
Within our solar system quite a bit of exploration has been done by spacecraft including orbiters and landers. Planets outside our solar system will be difficult or impossible to explore with spacecraft in our lifetimes, so astronomers and astrobiologists use other techniques to search for signs of life on these planets. In particular, astronomers are interested in planets within the habitable zone of stars.
The inner planets (those planets that orbit close to the sun) are quite different from the outer planets (those planets that orbit far from the sun). 1  The inner planets are: Mercury, Venus, Earth, and Mars. 2  The outer planets include: Jupiter, Saturn, Uranus, Neptune, and Pluto (a dwarf planet).