How Long Until the End of the World?

Jack sent me this article, which roughly suggests maybe 5 billion years until the earth is swallowed up by the sun. Maybe.

The Sun is midway through its stable hydrogen burning phase known as the main sequence. But when the Sun enters the red giant phase in around 5 billion years things are going to get a lot rougher in the Earth-Moon system.



... If the Sun's photosphere reaches Earth, our planet too will experience drag and spiral into the Sun to be incinerated.



There are possible natural alternatives, however.



If the Sun as a red giant sloughs off enough material before Earth evaporates, our planet will be revealed from its stellar cocoon in a Moon-less guise. Earth, robbed of its companion, would undertake a lonely vigil as the Sun turns eventually into a stellar corpse called a white dwarf Sun, fading to black over the ensuing trillions of years.



Alternatively, if the swelling Sun loses 20 percent of its mass prior to it reaching our vicinity, both Earth and Moon could be spared incineration and remain together facing each other for eternity. The actual outcome remains a theoretical uncertainty because no red giant star has been observed during this crucial phase.

To all this, Chris asks,

The only question on my mind is how Al Gore is going to be able to connect it to cigarette smoking and anthropogenic climate change.