Orbits and How They Work

When a child throws a ball they are after a fashion, launching it into orbit. It just happens that the child is not high enough and cannot throw the ball hard enough to prevent that obit from being interrupted by the ball striking the ground. Orbits are all about interruptions, forces of nature working against one another, and a lot of going around in circles.

A Look at Orbits and How They Work

At its most basic, an orbit is when one object makes a path around another object under the influence of gravity, or another form of centripetal force. When a mobile phone call is bounced off a satellite in space, that satellite is in Earth orbit, making its way round and round the planet, in a state of nearly constant falling. The reason it doesn’t finish falling and crash on to the planet’s surface is due in part to the fact that the Earth keeps running away from it.

When that child throws the ball it starts out going sideways, perpendicular to the ground. As the force of gravity pulls on it, it begins to fall downwards. If that same ball was shot out of a cannon it would go quite a lot further, as the curvature of the Earth falls away from the ball during its travel. A well used model involving a cannon atop a mountain high enough to escape Earth’s atmosphere is often used to illustrate this concept, as well as the different types of orbits.

No Circles

While there are circular orbits, there are not any in our solar system. Orbits in our solar system of planets, satellites and even comets are elliptical. An ellipse is a shape more egg shaped than a circle, but one with mathematical constants. The Earth is in an elliptical orbit around the Sun, a fact that was pointed out by Johannes Kepler around 1610, who was able to prove mathematically by his three laws of planetary motion.

The first law was that orbits are elliptical and that the sun is not the centre of the orbits, but rather one of the focal points. The second law showed that the speed of an object in an elliptical orbit—such as Earth—is not constant, but rather increases when it gets closer to the focus and decreases as it gets further away. The third law shows a mathematical constant shared by all planets that orbit the sun.

If it were not for the gravity of the Earth, the Moon would fire off into space in an instant, following the urges of momentum propelling it by centripetal force. As the Moon tries to escape, Earth’s gravity pulls it Earth-ward, but it does not crash into its mother planet because Earth continuously falls away from it. Thus the orbital dance will continue indefinitely, until some other force causes the orbit of one or the other body to change.

Orbital Decay

A scary thought when it comes to the relationship of the Earth and the Moon is orbital decay, which is what happens when forces slowly influence the orbit of one object until its speed slows enough to be more fully captured by gravity. In an elliptical orbit there is a point called periapsis, which is the point where the orbiting objects come closest to each other. Should one object come close enough to the atmosphere of another it will cause drag, slowing the speed of the first object. If this continues to happen over and over the orbit will decay until the objects intersect.

Final Thoughts

The spinning dance of the planets, moons and stars are the measuring sticks by which scientists can examine many objects in space. An object’s orbit—including the speed and shape--- can tell an astronomer observing it from millions of kilometres away the presence of another object millions of more kilometres away.

Related Articles in the 'Our Solar System' Category...

• A Guide To The Outer Solar System
• How Planetary Surfaces Are Formed
• Observing Dark Matter And The Lifespan Of The Universe
• Origins of the Solar System
• Planetary Atmospheres
• The Asteroid Belt
• The Discovery of our Dented Solar System
• The Dwarf Planets
• The Gas Giant Planets
• The Kuiper
• The Rocky Planets