If you have an object, say a planet, orbiting another object (a star), then everything is relatively simple. The orbit may be circular or more elliptical (elongated) or have many other mathematical shapes. The time required for one rotation of the star remains relatively constant.
Now imagine that there is a second object orbiting the star. Let’s say it’s an asteroid. It can also move in a circular or more elliptical path. When viewed from the outside, it will be seen that both of these objects follow their paths at different speeds and in different time periods.
And here comes the weirdness. Let’s assume that the asteroid’s orbit is very similar in size to the planet’s orbit, but slightly more elliptical. Both the planet and the asteroid orbit the star, completing each orbit in the same amount of time. But sometimes the asteroid will spin slightly faster than the planet, and sometimes slower.
If you look at the asteroid from the planet’s perspective, it will appear to be moving around it. This is very similar to the movement of the Moon. However, this is an illusion because the asteroid does not actually orbit the planet. Instead it moves around the Sun.
The analogy of this movement is the scenario where you are driving in the middle lane of a three-lane road. Imagine that the car will first pass in front of you from the left side, pass you and change lanes to the right. Then it will slow down, pass behind you, accelerate and pass you again on the left.
Objects with similar orbits are known as quasi-satellites or quasi-moons. But these are not actually satellites because they orbit a star, not a planet. Additionally, these objects are often too far away from gravity to be gravitationally bound to the planet.
Earth has several such satellites. For example, 469219 Kamoaleva is an asteroid about 50 meters wide with an orbital period of 1,002 Earth years; that is, it is only 17 hours longer than the Earth’s period.
This proves once again that our ideas about events are much more flexible than they seem. Therefore, in science it is better to avoid rigid definitions and allow yourself to be flexible in your thinking.
Source: Ferra
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