Read the stories of the Book “Have you seen the great bear in the sky?” (Scorza) that we have provided below. In order to quantitatively measure and record the brightness of the stars in tables and to communicate his results to other astronomers, he introduced a magnitude scale that ranges from 1 to 6: The brightest stars had a magnitude of 1, the faintest ones 6. When Hipparchus started observing the stars, he noticed also that they had different brightnesses. Because it takes 26.000 years for the Earth’s axis to complete a precession cycle, it is too slow to be noticed within a few years. In reality it is the Earth’s axis that precesses like a spinning top. While observing and measuring the positions of the constellations during spring, and by comparing his measurements with those obtained by the Babylonians thousands of years earlier, Hipparchus concluded that the whole sphere of the sky with the constellations on it shifts. 24 Earth procession (Credits: Earth and Planetary Magnetism Group Zurich) After this discovery, Hipparchus kept observing the sky in case another new star would appear!įig. This was a huge surprise since it had been thought that the sky was eternal, perfect and unchangeable. We now think that this star was actually a supernova - a dying star undergoing an enormous explosion. In 135 BCE Hipparchus reported the appearance of a “new star” in the sky. He compiled the first comprehensive star catalogue of the western world, and possibly invented the astrolabe, which he used to produce his star catalogue. Hipparchus is often considered to be one of the greatest astronomical observer of old times.
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