Lunar eclipse occurs when the Earth is between the Sun and the Moon and the three of them lie in a straight line. The above diagram shows the positions of the Moon, Earth and Sun during the eclipse of the Moon. When the Earth is between the sun and the Moon and the three of them lie in a straight line, sunlight cannot pass through the Earth because it is an opaque object. As sunlight travels in straight lines, it cannot bend around the Earth. Therefore, the Earth blocks the sunlight from reaching the Moon. The Earth's shadow will cover the Moon's surface and causes a lunar eclipse. Lunar eclipse can be observed with the naked eye. It can only be observed by people on the side of the Earth which is having night-time. Lunar eclipse can only occur at the phase of full Moon. When the Earth blocks sunlight, it produces a shadow with two regions, the umbra and the penumbra.