The Sun is currently in its main sequence phase, where it fuses hydrogen into helium in its core. As it ages, the Sun will eventually exhaust its hydrogen fuel and begin to expand, transitioning into a red giant. This will have significant consequences for Earth and the solar system:

Consequences of the Sun's Expansion:

* Increased Solar Radiation: The Sun will become much larger and brighter, emitting significantly more radiation. This will cause Earth's surface temperature to rise dramatically, making it uninhabitable for most life forms.

* Evaporation of Oceans: The increased heat will evaporate Earth's oceans, leaving a dry and barren planet.

* Swallowing of Inner Planets: As the Sun expands, it will engulf the inner planets, including Mercury, Venus, and potentially Earth.

* Change in Solar System Dynamics: The expansion of the Sun will alter the orbits of the remaining planets, potentially causing instability and collisions.

Timeline:

* Red Giant Phase: This phase is expected to begin in about 5 billion years.

* Earth's Fate: Earth will likely be engulfed by the Sun in about 7.5 billion years.

Note: The exact timing and details of these events are still uncertain, as they depend on complex astronomical models. However, the general consequences of the Sun's expansion are well understood.

Beyond the Red Giant:

After the red giant phase, the Sun will eventually shed its outer layers, leaving behind a small, dense white dwarf star. This white dwarf will cool down over billions of years, eventually fading into darkness.

In summary, the Sun's expansion will be a dramatic event with catastrophic consequences for Earth and the inner solar system. While it is still billions of years away, it highlights the finite lifespan of stars and the dynamic nature of our universe.