From Geocentric To Heliocentric

In contrast to this, the Earth is imperfect and constantly changing. Aristotle thought that comets must exist inside of the Earth’s sphere, as it was obvious that they didn’t move in perfect circles. The assimilation of Hipparchan observations can no longer be discussed under the aspect of plagiarism.

Ptolemy does this rather cleverly by replacing the abstract geometrical theories by mechanical ones. It may seem strange to the modern reader that someone who wrote such excellent scientific books should write on astrology. Bradley knew that if he could measure the angle that the stars appeared to move, then he could determine how far away they are using trigonometry. Tycho had failed to observe this movement, and Bradley’s observations were not able to provide evidence of parallax either, but he did observe stellar aberration.

People that are moving at a constant velocity are said to be in an inertial frame of reference, and people that are accelerating are said to be in a non-inertial reference frame. Galileo’s relativity is only applicable to objects that are stationary or travelling at constant velocities. You can feel the effect of acceleration , and this means that acceleration is not relative; there are always experiments that can determine if an object is changing velocity and hence accelerating. Despite this, Galileo’s observations were verified within a year by the Italian astronomer Antonio Santini. Galileo’s claims were accepted within a year, even though he didn’t give enough information for others to replicate his results. Galileo was concerned that if others knew how to build a telescope like his, then they would beat him to all the potential new discoveries.

If something is moving in a circle, then the direction can be measured in degrees. One full circle is 360°, which is equal to 2π radians, and so something moving at 8 m/s in a full circle, for example, will change velocity (Δv) by 2π × 8 m/s. When objects move in a circle, they change direction, and so can change velocity without changing their speed. This acceleration is known as centripetal acceleration , and it is always directed towards the centre of the circle. In the case of the Earth’s rotation at the equator, the distance is the circumference of the Earth at the equator, which is about 40,030 km, and the time is equal to one day.

Since its discovery in 1930, until 2006, Pluto was counted as the ninth planet in the solar system. In 2006, the International Astronomical Union reclassified it as a ‘dwarf planet’, and our Solar System dropped from having nine planets to eight. An Egyptian astronomer called Ptolemy (AD ) described one of the earliest ideas for how the Solar System is structured.

However many still felt there was something not quite right about how they viewed their model. The orbits of inner planets seemed very elaborate – see the apparent orbit of the inner bodies image. Eudoxus’ model placed a spherical Earth at the centre of the universe. The Sun, planets, and stars were then placed in giant transparent spheres surrounding it. A model of the universe that has the Earth at the centre is known as a geocentric model of the universe. Tycho Brahe was an astronomer whose personal life was as varied as his astronomical one.