Glossary
Circular Orbits
A specific type of orbit where an object moves in a perfectly circular path around a central body, maintaining a constant speed and radius.
Example:
Many communication satellites are placed in Circular Orbits around Earth to ensure consistent coverage.
Elliptical Orbits
An orbit where an object follows an elliptical path around a central body, with the central body located at one of the ellipse's foci.
Example:
Comets often follow highly Elliptical Orbits, bringing them very close to the Sun at one point and then far away.
External Forces
Forces originating from outside a defined system that can influence or perturb the motion of objects within that system.
Example:
The gravitational pull from Jupiter can cause slight deviations in the orbit of an asteroid, acting as an External Force.
Geostationary Orbits
A specific type of circular orbit directly above the Earth's equator, where a satellite's orbital period matches the Earth's rotational period, making it appear stationary from the ground.
Example:
Weather satellites and television broadcast satellites are often placed in Geostationary Orbits to provide continuous coverage to a specific region.
Gravitational Constant (G)
A universal constant that quantifies the strength of the gravitational force between masses, appearing in Newton's Law of Universal Gravitation.
Example:
When calculating the gravitational pull between two asteroids, you would use the Gravitational Constant (G) along with their masses and separation.
Gravity Assists (Slingshot Effect)
A maneuver that uses the gravitational pull of a planet to alter a spacecraft's speed or direction, conserving energy and momentum.
Example:
The Voyager probes used multiple Gravity Assists from Jupiter and Saturn to gain the speed needed to travel to the outer solar system.
Initial velocity
The starting speed and direction of an object, which significantly influences the shape and stability of its subsequent orbit.
Example:
If a rocket's initial velocity is too low upon launch, it might fall back to Earth instead of achieving orbit.
Kepler's First Law (Law of Ellipses)
States that all planets move in elliptical orbits with the Sun at one of the two foci.
Example:
Mars's path around the Sun is not a perfect circle but an ellipse, as described by Kepler's First Law.
Kepler's Second Law (Law of Equal Areas)
States that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time, implying that planets move faster when closer to the Sun.
Example:
As a planet approaches its closest point to the Sun (perihelion), its speed increases, ensuring that the area swept by its radius vector over a given time remains constant, in accordance with Kepler's Second Law.
Kepler's Third Law (Law of Harmonies)
States that the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
Example:
Using Kepler's Third Law, astronomers can calculate the orbital period of a newly discovered exoplanet if its semi-major axis is known.
Newton's Law of Universal Gravitation
This fundamental law states that every particle in the universe attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
Example:
The force of attraction between the Earth and the Moon, which keeps the Moon in orbit, is described by Newton's Law of Universal Gravitation.
Orbital Period
The time it takes for an orbiting object to complete one full revolution around its central body.
Example:
The Orbital Period of Earth around the Sun is approximately 365.25 days, defining our year.
Orbital Velocity
The speed at which an object travels along its orbit, determined by the mass of the central body and the orbital radius.
Example:
To maintain a stable circular path, a satellite must have a precise Orbital Velocity that balances gravitational pull with centripetal force.
Semi-major axis
Half of the longest diameter of an ellipse, representing the average distance of an orbiting body from its central body.
Example:
For Earth's orbit, the semi-major axis is approximately 1 Astronomical Unit (AU), defining the average distance from the Sun.