The amount of hydrogen in the sun is decreasing because it is being fused into helium in the sun's core. This process, called nuclear fusion, is the source of the sun's energy.

Here's how it works:

1. High pressure and temperature: The sun's core is incredibly hot (around 15 million degrees Celsius) and under immense pressure.

2. Hydrogen nuclei collide: This extreme environment forces hydrogen nuclei (protons) to collide with each other at extremely high speeds.

3. Fusion: When these protons collide with enough force, they overcome their electrostatic repulsion and fuse together. This fusion process releases a tremendous amount of energy, primarily in the form of light and heat.

4. Helium formation: During fusion, four hydrogen nuclei (protons) combine to form one helium nucleus, releasing energy in the process.

Since hydrogen is the fuel for this fusion process, the sun's supply of hydrogen is constantly being depleted as it is converted into helium.

How long will the sun's hydrogen last?

The sun has enough hydrogen to continue fusing for about 5 billion years at its current rate. After this, the sun will enter its red giant phase, where it will expand and cool, eventually becoming a white dwarf.

In short, the sun's hydrogen is decreasing because it is being consumed in the process of nuclear fusion, which powers the sun and releases the energy that sustains life on Earth.