Looming some 384.400 km (239,000 miles) from the Earth, with a diameter of 3476 km (2,160 miles) and a mass of 7.35e22 kg. shines the Moon. The Moon is the brightest object in the night sky and only second in brightness to that of the Sun. Its mean density is only 3.34 times that of water. It has no real atmosphere and no magnetic field of its own and is the only natural satellite of our planet Earth. In fact, the Moon is next to the largest moon in our solar system; the Earth and Moon can almost be said to be a double planet. The Moon undergoes extremes in temperature: it is alternately scorched to +110 degrees celsius during the day and frozen to -180 degrees celesius at night. Many of us have seen its eclipses and occultations. The Moon shines by reflected sunlight as it passes through each of its familiar phases, and the Moon (with a little help from the Sun) also controls the ocean's tides.