# How far are the Earth and the Moon

#### In this article you will find out how long it takes to get to the Moon, how far the Earth is from this satellite and how distances are measured.

Knowing how far the Moon is from planet Earth is one of the great questions of the world, which has been wanted to be answered with very specific studies. In reality, the distance between the Earth and the Moon is not a unique number, as it depends on the position of the planet and its satellite. So many, during the last century, have asked themselves "How long does it take to get to the Moon?" and have done experiments in this sense.

#### The study of lunar measurement

The first studies in this time date back even to the ancient Greeks, who using lunar eclipses had ascertained that the distance was about 60 Earth radii: a measure very close to the value measured today with advanced instrumentation. One of the first scientific experiments was that of Doug Currie in 1969 carried out an experiment of laser measurement of the Moon, to understand how long it takes to get to the Moon.

#### The distance Earth-Moon

On the other hand, to the question "How long does it take to get to the Moon?" there is no single answer, because although there is an average distance of 384,400 km, it can vary from a minimum of 363,300 up to a maximum of 405,500 kilometers. In fact, the Moon orbits the Earth with a motion that lasts one sidereal month, which is equal to 27 days, seven hours, 43 minutes and 12 seconds. Since the orbit is elliptical, the distance depends on where the Moon is at that moment.

#### How long does it take to get to the Moon

Once the distance was determined, it was important to figure out how long it takes to get to the Moon, in order to be able to plan trips to it. In reality, this question cannot have an unambiguous answer. The first expedition lasted 3 days outward, while only 11 hours in the return. Today the Space Shuttle takes about 18 hours.

#### The first trips to the Moon

The measurement of the Earth-Moon distance was also preparatory to travel to the satellite. The advent of space exploration also opened up the possibility of exploring the Moon, one of the projects that was fully part of the space race between the United States and the Soviet Union. The first time man set foot on the satellite was July 20, 1969. Neil Armstrong, commander of Apollo 11, was the first astronaut to set foot on the lunar surface.

The landing was commemorated with a plaque left on the lunar surface. Several missions followed, six in all, but after the 1970s the moon landings lost interest, although automated probe landings continued for a few more years. Lunar exploration then resumed around the 2000s, although always and only with remotely controlled probes. In these years also China started its own lunar explorations.

#### The study of the Moon

Answering the question "How long does it take to go to the Moon?" was only the first of the great questions that human beings have asked themselves about their satellite. In fact, very detailed studies have been carried out on the Moon, which are still going on in our years.

One of these is the one concerning the gradual removal of the Moon from the Earth: as emerged from the Luna Laser Ranging experiment, every year the satellite moves away from our planet by 3.8 cm. This means that the Earth-Moon distance is also changing. The phenomenon depends on the strength of the tides. This means that immediately after its formation, the Moon was much closer to Earth than it is now.

As part of the study of the Moon, its composition is also very fascinating. Its internal composition has not been fully identified, but in the core there should be metallic iron, along with nickel and sulfur.

#### The surface of the Moon

One of the most interesting topics of discussion after the Earth-Moon distance, is that of the lunar surface. Over the millennia, in fact, human beings have tried on several occasions to make lunar maps. The first one dates back to 3000 BC, when an illustration was drawn on a tomb. But a more precise conception of these maps came from the seventeenth century, when astronomers began to draw the visible face.

The surface of the moon is divided between seas and craters, although the former are not composed of water but are actually basaltic plains. In any case it is assumed the presence of water in the lunar craters. And instead sure that there are formations of ice. It is hypothesized besides that of the water can be contained inside the satellite.