The Sun became a star about 4.5 billion years ago, when it started to fuse hydrogen into helium in its core. Astronomers have estimated that the star with the mass of the Sun has enough hydrogen to maintain stable fusion reactions over 10 billion years. After that the core will become mostly helium, the Sun will become unstable, it will swell and become a red giant. Eventually it will expel its upper layers that will form a planetary nebula and its core will collapse into a white dwarf.

How long before the Sun will exhaust hydrogen in its core and become a red giant?

Planetary orbits are 

Which have more moons on average? 

Solar energy leaves the core of the Sun in the form of 

Jupiter nudges the asteroids through the influence of 

Scientists estimate the central temperature of the Sun using 

Looking

at the pattern on the diagram, decide how much dimmer the star with

brightness B = 1 at a distance d = 1 would look to us if it was placed

at the distance of d = 4?

Which of these stars has the shortest life expectancy? 

What happens to a cloud’s thermal pressure if its temperature falls while its density rises? 

Which of these stars has the hottest core?