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# What's the distance between Earth and Sun?

Have you ever heard how the Sun to Earth distance is being calculated ? When were the first attempts to count it? What is Astronomical Unit and where it is used?

The Sun is the most important constituent of life on our planet. Without sun it is impossible to imagine how humankind can survive. We are highly dependant on it even if we don`t realize it.

How far the Earth is from the Sun? What is the distance between Earth and Sun? It seems to be a simple question.  But in reality it is the subject of controversy scientists for over a hundred years.

How to decide from which point from the Earth to measure? How to define in which way a distance to the sun must be calculated - before its fumes or flames?

Astronomical unit - a unit of measurement of distance in astronomy, which is approximately equal to the average distance from the Earth to the Sun. It was first calculated by astronomer and engineer Giovanni Cassini in 1672. He compared his measurements on Mars, with the observations of his colleague Jean Richer, helping them to determine the third value - the distance between the Earth and the Sun (Sun Earth distance), equal to 146 million kilometers. But in fact this number is parallax - a combination of constants that transform angular measurements in the distance.

From the early childhood, everyone knows that the sun is a star that is very far away from our planet and it is a huge glowing ball. But only a few can answer on the question of what is the distance between Earth and Sun.

One reason for this is that when we look at the sun, it seems a small bright circle in the sky, but in reality, its diameter about a hundred times bigger than the diameter of our Earth and the Sun volume exceeds the volume of the blue planet more than a million times.

Exact distance

In fact, the Sun is about 150 million kilometers from our planet. This distance varies due to the fact that the earth's orbit is elliptical. The biggest distance equal to 152 million kilometers is recorded in July, and the lowest - in January and is 147 million kilometers. Cut 152 million kilometers long is called aphelion, and the minimal amount of 147 million kilometers is called Perigee. For the comparison, the distance between the Earth and its companion moon is only 384 thousand kilometers.

Measuring the distance from the Earth to the sun has been started in the time of Ancient Greece, but the calculation methods were quite primitive. In the Middle Ages for measuring the distance they began to use the parallax method, however, even with it, they could not achieve significant results.

First numbers

First who have measured the distance to the Sun were astronomers Riher and Cassini. They did this with the help of observations of the position of Mars in the starry sky, as well as using geometric calculations. As a result, they got a distance equal to 139 million kilometers, which is, of course, is understated value, but it is worth considering that the calculation was made in 1672.

The big breakthrough in the space industry happened due to the Second World War, namely in the second half of the twentieth century, when the scientific and technological revolution took place. There were brand new methods for measuring cosmic distances, including radar method which took an important place.

The essence of this method is that the direction of the cosmic body is transferred to the momentum, reaching him, part of the pulse is reflected back to Earth, where special devices took it and analyzed. With the help of information about for what period of time the momentum goes the distance from the Earth to space body and back, scientists made the most accurate calculation of distances.

### Measurement

Also for the measurement of space more specific values are often used, such as a light-year and parsec. A light year is commonly understood as the length that light travels in a year. The speed of light is approximately 300 000 000 m / s, therefore, the light quantity is equal to the year 9,46073047 × 10 km * 12.

If you measure the distance between the Earth and the Sun in light years, it will be about 8 light-minutes. For such a time interval the light which radiates the sun reaches the earth's surface.

Often the light year and parsec is used to measure and study distant cosmic objects, such as major stars from different major constellations.