在他的望远镜的帮助下，伽利略发现即使是月亮也包括山，谷和洞穴等。在月球上，这些东西与地球上的东西一样有意义。他直接看了看太阳，发现了一些不足之处 – 最突出的就是被称为太阳黑子的黑色污点。他继续观察这些太阳黑子，发现这些太阳黑子的外观每天都在变化，从这个伽利略得出的结论是，太阳在一个月内旋转一次。他建议太阳绕一个近似垂直于黄道平面的轴旋转。
With the help of his telescope, Galileo found that even Moon consists of mountains, valleys and caves etc. At moon too these things were equally meaningful as on the Earth. He looked at sun directly and discovered several inadequacies – the most prominent one was the dark stains which were named as sunspots. He kept on observing these sunspots and found that the looks of these sunspots kept on changing every day, from this Galileo concluded that sun rotates once in a month. He proposed that the sun rotates around an axis which is approximately vertical to ecliptic plane.
During his observations Galileo also noticed four tiny points of light which were revolving around the Jupiter. He assumed those to be moons (Gal & Chen, 2011). The four points were so small that they could not be seen through bare eyes. According to Galileo, the other planets in the universe also had moons and this was the biggest support Copernican theory. From this it was proved that Earth is not centre. According to Copernican theory too Earth and the other planets revolves around the Sun and hence Earth is not the centre of all the things.
Galileo also supported the same with one of his findings with respect to planet Venus. According to Ptolemaic theory, the planet Venus stays between the Earth and the Sun. Due to this reason it would always display a hemispherical phase as the maximum part of it faces the Sun and be illuminated. According to Copernican theory the planet Venus occasionally stay between Earth and Sun and during that time, it would have a new a semicircular phase (Lattis, 2010). But there are occasions when parts of the part on which it lies be on the opposite side of the Sun and this is the time when complete phase is seen.