JohannesKepler (1571-1630) was an important German astronomer and mathematician and responsible for major contributions in the field of astronomy and astrophysics. Developed three laws that describe the motion of bodies trapped in gravitational interactions.
Kepler's laws were developed between 1609 and 1618, after careful analysis of the observations made by the Danish astronomer Tycho Brahe (1546-1601) and the study of planetary systems previously carried out by great names in astronomy, such as Ptolemy and Nicolas Copernicus. Kepler's Laws were of great importance for the development of Universal gravitation of Newton. Newton studied Kepler's work and was able to explain it using the equations of gravitation.
Kepler's 1st Law, also known as “law of orbits”, is stated as follows:
“All planets move around the Sun in elliptical orbits, with the Sun at one of the focuses.”
Kepler realized that the orbital speed of planets around the Sun was not constant. Because of the shape of the orbits, there were points at which the distance from the Sun increased or decreased and this change was responsible for
variations at the speed of the planets orbiting the Sun.We say that upon reaching the smaller distance to Sun, the planets are in the perihelion and when they reach the point of orbit moredistant, they are in aphelion.
The following figure shows the positions THE and B, which are respectively the perihelion and aphelion of the orbit of the planets around the Sun. the positions X they are the focuses gives Ellipse. The Sun always coincides with one of the focuses of the ellipse.
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Orbit eccentricity
The eccentricity of the ellipses is given by the reason between the distance between the twofocuses it's yours semi axisbigger. For elliptical shapes, this value is always between 0 and 1. The closer to 0, closer to a circle perfect is the planet's orbit. Earth's orbit is littleeccentric, almost circular, and this made it difficult to see its real shape for a long time.
Check the eccentricity values for the orbits of the planets in the Solar System:
Planet |
Eccentricity |
Mercury |
0,2056 |
Venus |
0,0068 |
Earth |
0,0167 |
Mars |
0,093 |
Jupiter |
0,048 |
Saturn |
0,056 |
Uranus |
0,046 |
Neptune |
0,0097 |
bodies in earth orbit
the orbit of some satellites, natural or artificial, around the Earth it can also be elliptical and quite eccentric. When these satellites are at the lowest height in relation to Earth, we say they are in the perigee. When they are as far away as possible, they will be in the heyday.
By Rafael Hellerbrock
Graduated in Physics
Would you like to reference this text in a school or academic work? Look:
HELERBROCK, Rafael. "Kepler's First Law"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/primeira-lei-kepler.htm. Accessed on June 27, 2021.
