#xkcd 2971

[todays-xkcd]

If we can get a brood of 13-year cicadas going, we might have a chance at making this happen before the oceans evaporate under the expanding sun.

Celestial Event [Explained]

Transcript Under the Cut

Approximate frequency in my area Active northern lights: 20 days per solar cycle A naked-eye "Great Comet": 2 months every 50 years Total eclipse: once every 350 years Clear skies: 50% of the time 17-year cicada emergence: 2 months every 17 years

opening bracket

20 days over 11 years multiplied by

2 months over 50 years multiplied by

1 over 350 years multiplied by

one half multiplied by

2 months over 17 years

closing bracket to the power of -1

equals 4.3 billion years

[Caption below the panel:] Every 4 billion years or so, my neighborhood gets to see a really spectacular show.