4 times 10 to the ninth is 4 billion (4,000,000,000) - when our sun is into expansion as a red giant.
And enigmatic chapter title and an enigmatic opening line. Questions
The sun, our life-sustaining star, is currently in its stable phase as a main sequence star. During this phase, it efficiently converts hydrogen into helium in its core. This stable period lasts for approximately 8 billion years. Our solar system, which is around 4.5 billion years old, has already witnessed more than half of the sun’s stable lifetime.
However, as the sun exhausts its hydrogen fuel, it will undergo significant changes. When the core runs out of hydrogen, it will be left with helium. Unfortunately, the core won’t be hot or dense enough to burn helium directly. Gravitational forces will take over, compressing the core. As a result, the sun will start burning hydrogen in a shell around the dead core, which still contains helium. This transition marks the sun’s transformation into a red giant.
During the red giant phase:
The outer regions of the star will expand outward due to compression in the core.
The burning hydrogen in the shell around the core will significantly increase the sun’s brightness.
The sun’s surface will cool down, transitioning from white-hot to red-hot.
Earth’s fate is intertwined with this cosmic drama. As the sun becomes a full-blown red giant, its surface will likely reach the current orbit of Mars. Although Earth’s orbit may also expand slightly, it won’t be enough to save our planet from being drawn into the sun’s surface. Consequently, Earth will rapidly disintegrate, and our fiery demise will unfold.
P. 40 says in 5.5 years on earth, 500,000,000 years passed outside. When 4 billion years have passed outside, how many years will have passed in earth? Consider 5.5 is to 500 million as X is to 4 billion.
By cross multiplication, 5.5 times 4 billion = 500 million times X. Use math to solve for X.
So 22 billion divided by 500 million = 44. Thus 40 to 50 years before solar fuel exhaustion.
