Question

what causes aurora?
charged particles from solar winds colliding with earths magnetic field
the reversal of earths magnetic field.
the fusion of hydrogen to helium.
changes in the number of sunspots.

Explanation:

Auroras occur when charged particles from solar winds collide with Earth's magnetic field. These particles interact with gases in the atmosphere, creating the light displays. The reversal of Earth's magnetic field is a rare geological event not related to auroras. Hydrogen - to - helium fusion occurs in stars like the Sun, not in Earth's atmosphere. Changes in sunspot numbers relate to solar activity levels but do not directly cause auroras; it is the charged particles from solar winds (which can be more prevalent during high sunspot activity) that are the direct cause.

Answer:

Charged particles from solar winds colliding with Earth’s magnetic field.