Here's why:
* Red Giant Phase: As the Sun ages, it will run out of hydrogen fuel in its core and start fusing helium. This causes the Sun to expand dramatically, becoming a red giant.
* Ejection of Outer Layers: During the red giant phase, the Sun's outer layers become unstable and are ejected into space. This ejected material forms a shell of gas and dust around the Sun.
* Planetary Nebula: The intense ultraviolet radiation from the Sun's hot core ionizes the ejected gas, causing it to glow brightly. This glowing shell of gas is known as a planetary nebula.
It's important to note that while the name "planetary nebula" sounds like it has something to do with planets, it doesn't. The name comes from early astronomers who mistook the round shape of these nebulae for planets through their telescopes.
