The moon is Earth’s only natural satellite. The moon is a cold, dry orb whose surface is studded with craters and Stewn with rocks and dust and has no atmosphere. Recent lunar missions indicate that there might be some frozen ice at the poles. The far side of the moon was first observed by humans in 1959 when the unmanned Soviet Luna 3 mission orbited the moon and photographed it. Neil Armstrong and Buzz Aldrin (on NASA’s Apollo 11 mission, which also included Michael Collins) were the first people to walk on the moon, on July 20, 1969. The moon’s diameter is 2140 miles (3476 km), 27% of the diameter of the Earth. The gravitational tidal influence of the moon on the earth is about twice as strong as the Sun’s gravitational tidal influence. The Earth: moon size ratio is quite small in comparison to ratios of most other planet: moon systems.
There have been many missions to the moon, including orbiters missions and moon landings. NASA’s Apollo missions sent people to the moon for the first time. Apollo 11’s LEM (Lunar Excursion Module) landed on the moon on July 20, 1969 with Neil Armstrong and Edwin “Buzz” Aldrin. Neil Armstrong was the first person to set foot on the moon. His first words upon stepping down the Lunar Module’s ladder onto the lunar surface were, “That’s one small step for man, one giant leap for mankind” . Aldrin described the lunar scenery as ” Magnificent desolation”.
The origin of the Moon
Most scientists believe that the moon was formed from the ejected material after the Earth collided with a Mars sized object. This ejected material coalesced into the moon that went into orbit around the Earth. This catastrophic collision occurred about 60 million years after Earth itself formed (about 4.3 billion years ago). This is determined by the radioisotope dating of moon rocks.
The Moon’s Orbit
The moon is about 384,4000 km from Earth on average. At its closest approach the moon is 356,410 km from the Earth . At its farthest approach the moon is 406,700 km from the Earth. The moon revolves around the Earth in about 27 days 8 hours. It rotates around its own axis in the same amount of time. The Moon’s Orbit is expanding over time as it slows down. For example, a billion years ago, the Moon was much closer to the Earth and took only 20 days to orbit the Earth. Also, one Earth ‘day’ was about 18 hours long. The tides on Earth were also much stronger since the moon was closer to the Earth.
The Earth and the Moon are relatively close in size i.e. 4:1 in diameter and 81:1 in mass, unlike most planet/moon systems. Many people consider the Earth and Moon to be a double Planet system and that moon does not actually revolve around the Earth but around the Sun in concert with the Earth.
The moon’s mass is 7.35 x 1022 kg about 1/81 of the Earth’s mass.
The moon’s gravitational force is only 17 % of the Earth’s gravity. For example, a 45 kg person would weigh only 7.6 kg on the moon. The moon’s density is 3,346.4 kg/m³. This is about 3/5 the density of the Earth.
The temperature on the Moon ranges from daytime highs of about 130°C = 265°F to nighttime lows af about -110°C = -170°F.
The moon has no atmosphere. On the moon, the sky is always appears dark, even on the bright side. Also, since sound waves travel through air, the moon is silent as no sound transmission on the moon.
Scientists now think that the moon was formed when a Mars-sized object crashed into our planet about 4.5 billion years ago. The collision was so large that a huge spray of material was ejected into space. The orbiting ring of debris gathered itself into a sphere, and formed the moon.
Although the orbit of the Moon seems nice and stable, our only natural satellite is actually drifting away from us at a rate of 4 centimetres a year. This is happening because of the conservation of momentum in the orbit of the Earth.
You might know that the tides on Earth are caused by the gravitational pull of the Moon. But it’s not the only thing pulling at the Earth’s water, the Sun is helping out to. This is why we get very high and low tides from time to time.