| HotLiquidMagma.com A Practical Guide to Astronomy |
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Our Moon |
| Defining the Moon
The Earth's only known natural satellite, shines by the sun's reflected light. It revolving around the Earth from east to west in about 29.5 days with reference to the sun or about 27.3 days with reference to the stars. It has a diameter of 3475 km (2160 miles) and a mean distance from the Earth of about 384,000 km (238,700 miles). The moon is an airless spherical rock about 1/4 the size of the Earth. The moon has had a violent and turbulent history. Most of the craters on its surface were caused by meteoroids crashing into it about 3-4 billion years ago. The darker shades of the moon are called 'maria' (seas). These were caused by underground lava that flowed to the moon's surface. |
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This image of the north polar region was taken by the Galileo Orbiter in 1996. Courtesy of NASA.
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Gravity on the Moon The Moon is much smaller than the Earth and so it has a weaker gravitational pull. When the USA sent astronauts to the moon, they had to be weighed down to help them walk. It is gravity that causes ocean tides on the Earth to rise and fall. The gravity of the Sun and Moon pulls the Earth's oceans into bulges. The Earth rotates beneath these bulges causing two high tides per day. |
| Astronaut Edwin E. Aldrin Jr., lunar module pilot, is photographed during the Apollo 11 extravehicular activity on the Moon - July 1969. Courtesy of NASA. |
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