* Cool: They have a lower surface temperature than the Sun, typically around 3,500 - 5,000 Kelvin. This gives them a reddish appearance.
* Luminous: Despite their low temperature, they are very large and have a high luminosity. This means they radiate a lot of energy.
How are they formed?
Red giants are formed when stars like our Sun exhaust their hydrogen fuel in their core. This causes the core to contract and heat up. The outer layers of the star expand and cool, creating the characteristic red giant structure.
Examples of red giants:
* Betelgeuse in the constellation Orion
* Arcturus in the constellation Boötes
* Antares in the constellation Scorpius
It's important to note that red giants are not the coolest stars. There are even cooler stars called red dwarfs which are much smaller and less luminous than red giants.
