I believe that the three levels are:
1) primary or extractive: getting the resources. this includes for example producing milk (milking cows)
2) secondary: manufacturing: packaging the milk and treating it
3) tertiary: providing a service, for example bringing the milk to people's home!
Answer:
The most likely explanation is that the star is a member of an eclipsing binary star system.
Explanation:
An eclipsing binary star system takes place when two stars which are close to each other move in an orbit in which sometimes, one star can hide the light behind the other.
There are two types of eclipses depending on the orientation of the orbit and the size of the stars: the totals or the annular ones. It may also be the case that the eclipses are partial.
<em>Algol </em>is the best known eclipsing binary star, and the first of this kind to be discovered. Its interval between eclipses is 173 hours (2.9 days).
When this type of eclipses happens, the brightest star provides 92% of the light of the system, while the eclipsed only contributes less than 8%, and there is a third star, which is not eclipsed.
Therefore, if there is any star that has been bright most of the time, and during certain time intervals it becomes dimmer, that star is being overshadowed.
The ecliptic is the plane of Earth's orbit around the Sun. Hope this helped!
