The definition of “Kepler’s Laws”

Introduction

The objectives of this assignment is to introduce a parenthetical definition, sentence definition and expanded definition of a relatively complex term. The objectives are:

1. Appreciate the importance and role of definitions in technical writing
2. Understand how audience and purpose indicate the need for definition
3. Differentiate between the levels of details in the definition
4. Select the right level of detail according to the situation

Reading Situation

A professor is explaining about the foundation of astronomy to students in a lecture.

Parenthetical Definition

Kepler’s laws of planetary motion describes the orbits of planets around the Sun.

Sentence Definition

Kepler’s laws of planetary motion is composed of 3 laws that are using elliptical trajectories and explaining how planetary velocities vary.

Expanded Definition

History

Kepler announced his first two laws in 1609, having found them by analysing the astronomical observations of Tycho Brahe. Kepler’s third law was published in 1619. In 1621, he noted that his third law applied to the four brightest moons of Jupiter. After his death, Newton was credited with understanding that the second law is not special to the inverse square law of gravitation and still Kepler’s laws are regarded as a masterpiece of astronomy (Guillemin and Sternberg 5).

Analysis of Parts

To understand his laws completely, be sure to following three separated law:

1. The first law: The orbit of every planet is an ellipse with the Sun at one of the two foci.
2. The second law: A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.
3. The third law: The ratio of the square of an object’s orbital period with the cube of the semi-major axis of its orbit is the same for all objects orbiting the same primary.

Visuals

Figure 1 Description of Kepler’s law the first (“Kepler’s Laws”)

Figure 2 Description of Kepler’s law the second (“Kepler’s Laws”)

Figure 3 Formula of Kepler’s law the third (“Kepler’s Laws”)

Comparison and Contrast

Kepler’s laws corrected the model of Copernicus in these three sections:

1. The planetary orbit is not a circle with epicycles, but an ellipse.
2. The sun is not near the centre but at a focal point of the elliptical orbit.
3. Neither the linear speed nor the angular speed of the planet in the orbit is constant, but the area speed is constant (“Kepler’s laws of planetary motion”)

References