The next few million years:
* Slight increase in brightness and temperature: The Sun will continue to slowly brighten and heat up, gradually becoming more luminous. This is a natural consequence of its nuclear fusion processes. However, the increase in the next few million years will be very subtle and barely noticeable.
Over the next few billion years (not just millions):
* Red Giant Phase: In around 5-7.5 billion years, the Sun will exhaust its hydrogen fuel in its core. The core will contract, causing the outer layers to expand dramatically, turning the Sun into a red giant. This expansion will engulf Mercury, Venus, and potentially Earth.
* Helium Fusion: The core will become hot enough to fuse helium into carbon and oxygen. This process will be much more intense than hydrogen fusion, causing the Sun to expand even further and become significantly brighter.
* Planetary Nebula: Eventually, the outer layers of the Sun will be expelled into space, creating a beautiful, expanding shell of gas and dust known as a planetary nebula.
* White Dwarf: The remaining core of the Sun will shrink to a very dense, hot, and dim object called a white dwarf. This white dwarf will slowly cool down over trillions of years, eventually becoming a black dwarf.
Important Note: While the Sun will become a red giant and eventually a white dwarf, this is a very long process. The changes we'll experience in the next few million years will be minor. The Sun's eventual fate is something we don't need to worry about for billions of years.
