Answer:
A solar eclipse
Step-by-step explanation:
When the moon comes directly between the sun and earth, it causes a solar eclipse. This is when the moon casts a dark shadow onto Earth and starts covering up the sun during the daytime. A solar eclipse can be total or partial(the moon only covers up part of the sun).
Every year, there are 2 - 5 eclipses around the world. However, a total solar eclipse only happens every 18 months in a specific location on Earth.
Hundreds of people travel to see a total solar eclipse.
There are many videos online about solar eclipses, I suggest watching one or two to know more about them.