1. Main Sequence (Current Phase):
* Luminosity: Currently, the Sun's luminosity is steadily increasing by about 1% every 100 million years. This is due to the gradual increase in the Sun's core temperature as it fuses hydrogen into helium.
* Temperature: The Sun's surface temperature remains relatively stable during this phase, around 5,778 K (9,941°F).
2. Subgiant Phase:
* Luminosity: As the Sun runs out of hydrogen in its core, it starts fusing hydrogen in a shell around the core, causing the core to contract and heat up. This leads to a rapid increase in luminosity, about 1.5 times its current value.
* Temperature: The Sun's surface temperature will slightly decrease as it expands, reaching around 5,000 K (8,540°F).
3. Red Giant Phase:
* Luminosity: The Sun will continue to expand and cool, becoming a red giant. Its luminosity will increase dramatically, reaching about 2,300 times its current value. This is due to the expansion of its outer layers and the increased rate of fusion in the shell.
* Temperature: The Sun's surface temperature will decrease further, reaching about 3,000 K (5,040°F).
4. Helium Flash and Horizontal Branch:
* Luminosity: The Sun's core will become hot enough to ignite helium fusion in a process called the helium flash. This will temporarily increase the Sun's luminosity, but it will then stabilize as it enters the horizontal branch.
* Temperature: The Sun's temperature will increase slightly during the helium flash, but then stabilize as it settles on the horizontal branch.
5. Asymptotic Giant Branch (AGB):
* Luminosity: The Sun will expand further, becoming a red giant once again, and its luminosity will increase to about 5,000 times its current value. This is due to the fusion of helium in a shell around the carbon-oxygen core.
* Temperature: The Sun's surface temperature will continue to decrease, reaching around 2,000 K (3,140°F).
6. Planetary Nebula and White Dwarf:
* Luminosity: Eventually, the Sun will eject its outer layers, forming a planetary nebula. The remaining core will become a white dwarf, a very dense and hot object with a much lower luminosity than the Sun currently has.
* Temperature: The white dwarf will have a very high surface temperature, around 100,000 K (179,940°F), but will cool down over billions of years.
Summary:
As the Sun ages, it will become progressively brighter and cooler. It will experience a series of dramatic expansions and contractions, eventually ending its life as a white dwarf. While these changes are significant, they will occur over billions of years, far exceeding the lifespan of humans.
