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The distance Sun-Earth
Although the sun is only an insignificant star in our galaxy, it is the dominant object in our solar system and essential for life on Earth. A variation of only a few percent of its energy output would cause disastrous climate changes on Earth. Therefore, it is very important to observe and study the Sun and try to understand how it works.
In all human cultures the Sun played a major role and was thus observed by astronomers. Sunspots were observed already more than 2000 years ago by Chinese and Greek scientists.
Sunspots cannot only be used to measure the activity of the Sun but also its rotation.
With the formulation of Kepler’s third law at the beginning of the 17th century, it became possible for astronomers to determine the distances between Earth, Venus and the Sun by employing the parallax method to precise observations of Venus moving across the solar disc.