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.
Outer Planets. The next four planets out from the sun are Jupiter, Saturn, Uranus, and Neptune. They are collectively referred to as the Jovian planets (means Jupiter like). They are significantly different from the terrestrial planets. Besides being farther from the sun, the Jovian planets are much larger, are more gaseous, have lower densities, and all have some sort of rings. Their large sizes are responsible for increased gravity which can hold onto lighter elements like gases. A belt of asteroids (fragments of rock and iron) between Mars and Jupiter separate the four inner planets from the five outer planets. Pluto, which fits in with neither the terrestrial or the Jovian planets, is actually considered a Kuiper Belt object which we will see in more depth on the Kuiper Belt page.