Essay Example on Celestial Bodies: Their Motion and Gravity

An astronomical or celestial body is a naturally occurring object, which exists outside the earth's atmosphere and that can be perceived from within the universe. These are single, contiguous entities that may include planets, stars, asteroids, the earth, and the moon. Just like the planets and satellites, celestial bodies move in elliptical paths, obeying laws of motion. Forces of gravity attribute the motion of astronomical/celestial bodies. The motions of celestial bodies are influenced by forces such as diurnal, intrinsic, and retrograde motion, and also explained differently by Aristotle, Kepler, and Newton's.

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Celestial bodies exhibit two types of motion. These are either diurnal or intrinsic. For the first type, the entire celestial sphere, as well as the celestial bodies associated with it, rotates from the east to the west through the central axis of the earth. Diurnal motion, also known as reflex motion, results from the rotation of the earth wholly after every 24 hours. Due to the relative motion of the objects, their angular statuses are preserved (Soffel 303). On the other hand, the intrinsic type of motion is the result of the slow change of angular positions of the celestial bodies relative to each other (Nacozy & Victor 450). Some bodies identified with this type of motion, which is superimposed on diurnal motion comprise the sun, moon, and planets. A combination of the earth's motion around its orbit and about the sun; and the orbital movement of the moon and planets around the sun can be classified with the intrinsic motions of the objects. The result of these motions leads to absolute and apparent movements of the celestial bodies. Both are important to an astronaut investigating activities or the body.

There could be retrograde motion some other times out of complexity in movements of the celestial bodies. Retrograde motion commonly occurs when planets move in a backward motion, which is against its typical movement path (Kay, Stacy, & George 64). The factors contributing to retrograde motion is the combination of intrinsic and diurnal motions. For instance, earth's inhabitants can see a retrograde motion associated with Mercury and Venus since they move around the sun, whereas they are perceived from outside their paths. For the other outer planets, retrograde motion is perceived since the earth moves around the sun at its orbit at a faster rate compared to them, letting it pass some outer planets as they revolve within their orbits. Furthermore, for as long as the rotation of the solar magnetic field is related to the rotation of the sun, the direction of rotation of planets will be the direct opposite (Duboshin 28). This creates a reverse perception to a viewer at earth.

With the diurnal and intrinsic motion types, movement of planetary bodies is governed by the Kepler's Laws of astronomical motion. These are laws that explain the velocity of celestial bodies at a point in their orbit and at the period consumed for movement around its reference (Kay, Stacy, & George 73). The moon also obeys the Kepler's Law of celestial motion in its elliptical orbit around the earth (Kustaanheimo 54). These laws were founded upon observations by Tycho Brahe (Kay, Stacy, & George 69). The first law is the Law of Ellipses that tells how heavenly bodies are placed elliptically at their orbits with the sun being the focal area. The second of the laws "Law of Areas" explain how drawing a line from any planet to the sun will create equally swept out areas in the solar system and in equal periods. Newton's third law is mathematical and implies that the relativeness of the orbital period and the semi-major axis should be considered equal for all planets within the solar system. This is also referred to as the Law of Harmonies.

Besides Kepler's Laws, Newton's laws also explain the movement of planetary bodies outside the atmosphere. From his first law that comprised inertia, a body could always remain in constant motion unless acted upon by an external force (Soffel 303). This explains how celestial bodies can remain at their relative positions while moving around the sun. The basic of having celestial bodies is a combination of the application of force alongside energy consumption (Kay, Stacy, & George 77). Therefore, Newtonian mechanics in the concept of energy transformation and conservation law detailed explain astronomical body motion. Celestial body movement tends to comply with angular kinetic energy as opposed to the conservation of angular momentum (Hooker 339). The entire interpretation is such that a magnetic field is produced by the sun's rotation, which is not synchronous with the rotation of the sun, creating a similar effect to the planets. Additional, the concept of potential energy is a superfluous idea in Newtonian mechanics, and this cannot be related to energy (Kopeikin 1359). Therefore, the movement of heavenly bodies can be summed up and associated with conservative and non-conservative forces. The reason the second law does not associate with the movement of celestial bodies is the presence of inadequacies (Kay, Stacy, & George 78). The law, alongside some others that include the momentum theorem, angular momentum theorem, kinetic energy theorem, and the law of conservation of angular momentum does not sufficiently explain the placement of celestial bodies within their orbits, leave alone their movement (Hooker 339). Therefore, only motion laws by various theorists and energy conservation principles remain valid for planetary bodies.

Celestial bodies are objects under action of force, and these bodies apply force by themselves also. In that case, these bodies influence their motion that is attributed to the consumption of energy under the influence of a force. It is, therefore, evident that Newtonian mechanics are not universal concepts but remain an applicable concept in regards to slow movements of bodies within a predetermined short period, which is not ideal for planets. Associating Newtonian mechanics to the movement of celestial bodies creates a shortage of energy consumption, which is not comprehensive since only mechanical work can be ideally represented (Kopeikin 1370). Furthermore, Newton could not complete studies in his laws regarding objects under the action of a force. These same celestial bodies could have been the objects that apply force, which is not the case, hence, cannot be associated with the laws. Even while considering motion due to inertia, heavenly bodies cannot be termed as rational objects, which are comfortably placed under the influence of non-balance force. Therefore, these bodies do not meet the terms of inertial motion, leaving the gaps of tangential forces and first impetus. Even though there are these constraints, no many problems can be associated with Newton's conservation of momentum and the law of conservation of kinetic energy.

Aristotle also lamented about celestial motion within the field of terrestrial physics. According to theorist Aristotle, the earth can be regarded as the centre of the universe. It is the reference point for all other celestial astronomic bodies. From his studies, the sun, moon, and other planets orbited around the earth, with their orbits being a result of the paths on which they rest and move. His studies suggested an irregularity in planetary motion contrary to Kepler since he used more than a single sphere to describe the movements of one astronomic body. For him, there were 55 spheres, with the sphere of fixed stars, which existed at the periphery of the universe, making them 56. Presently, the sphere is regarded as cosmos, meaning a world. From a discontinuous movement of terrestrial matter, celestial bodies tend to move continuously with their motion being perceived as infinite and circular. Even though terrestrial bodies are corruptible because they come to be and pass away, astronomical bodies, which mainly comprise invisible spheres, are incorruptible. Some intelligence was associated with the spheres, which, on the contrary, led to motions of subordinate spheres. The motion was also partly caused by the movement of the spheres adjacent to the spheres, even though farther from the earth. Therefore, the general perspective from Aristotle is that astronomical movements are in part dependent, or independent of the movement of adjacent spheres.

Planetary bodies, which are bodies that naturally occur outside the earth's atmosphere, have their motion influenced and explained differently in ways such as diurnal, intrinsic, and retrograde motion; by theorists such as Aristotle, and by theories such as Kepler's Laws of planetary motion, as well as Newton's laws of motion. The motion of one heavenly body is no different from another since they are all governed equally. The only difference could be the perception of their movement from a relative position. Kepler's Laws of planetary motion are more explanative of the movement of celestial bodies more than Newton's laws, which are not comprehensive for such objects. However, many celestial bodies move; they always revolve around their orbits due to an external force.

Works Cited

Duboshin, G. N. "About the First Integrals of the Generalized Problem of Translatory-Rotary Motion of Rigid Bodies." Celestial Mechanics, vol. 6, no. 1, 1972, pp. 27-39., doi:10.1007/bf01237444.

Hooker, William W. "Equations of Motion for Interconnected Rigid and Elastic Bodies: A Derivation Independent of Angular Momentum." Celestial Mechanics, vol. 11, no. 3, 1975, pp. 337-359., doi:10.1007/bf01228811.

Kay, Laura, Stacy Palen, and George Blumenthal. 21st-century astronomy. WW Norton & Company, 2016.

Kopeikin, S. M. "Post-Newtonian Limitations on Measurement of the PPN Parameters Caused by Motion of Gravitating Bodies." Monthly Notices of the Royal Astronomical Society, vol. 399, no. 3, 2009, pp. 1539-1552., doi:10.1111/j.1365-2966.2009.15387.x.

Kustaanheimo, Paule. "Motor Integrals of a Generalized Kepler Motion." Celestial Mechanics, vol. 6, no. 1, 1972, pp. 52-59., doi:10.1007/bf01237447.

Nacozy, Paul, and Victor Szebehely. "The Computation of Relative Motion with Increased Precision." Celestial Mechanics, vol. 13, no. 4, 1976, pp. 449-453., doi:10.1007/bf01229097.

Soffel, Michael H. "Relativistic Equations of Motion of Celestial Bodies." Symposium - International Astronomical Union, vol. 172, 1996, pp. 303-308., doi:10.1017/s0074180900127573.