Extraterrestrial skies celestial equator to the North and in 2029 the North Pole of Uranus will be nearly pointed at the Sun. None of Uranus's moons would appear as large as a full moon on Earth from the surface of their parent planet, but the large number of them would present an interesting sight for observers hovering above the cloudtops. The angular diameters of the five large moons are as follows (for comparison, Earth's moon measures on average 31′ for terrestrial observers): Miranda, 11–15′; Ariel, 20–23′; Umbriel, 15–17′; Titania, 11–13′; Oberon, 8–9′. Unlike on Jupiter and Saturn, many of the inner moons
Stability of the Solar System essentially the distance from sun to earth). These are now known as the Kirkwood gaps. Some asteroids were later discovered to orbit in these gaps, but their orbits are unstable and they will eventually break out of the resonance due to close encounters with a major planet. Another common form of resonance in the Solar System is spin–orbit resonance, where the period of spin (the time it takes the planet or moon to rotate once about its axis) has a simple numerical relationship with its orbital period. An example is our own Moon, which is in a 1:1 spin–orbit resonance