Stone Suspension Bridges and Dim Suns

Obvious Errors in Science Fiction (and how to avoid them)


The Sun is incredibly bright - from the Earth it's about 10 billion times brighter than Sirius is from Earth, and it takes a lot of distance to dilute all that brightness. Even from Pluto's apogee, the Sun is significantly brighter (150 times!) than the full moon is from Earth. Even if you go out to the outer edge of the Oort cloud, 100,000 astronomical units away from the Sun, the Sun will still be the brightest star in the sky, though just barely, unless you go out directly towards Sirius; from 100,000 au out in the direction of Sirius, Sirius would be a bit brighter than the Sun.

Picture a story about some sort of culture surviving somehow at 100,000 au out - orbiting the Sun with a period of 30 million years. For the entire duration of the culture's existence, there have been two stars that dominate the sky - Sirius and the Sun, virtually exactly opposite each other in the sky. There's a story there, I'll bet.

I should note that I've used the simple approximation that the Sun's brightness will decrease as inverse r-squared. This is not precisely true, as near the Sun, the fact that the Sun is not a point-source does matter. But the approximation is good enough for our purposes - it would only make a real difference closer to the Sun than Mercury.

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