The planets almost fit between Earth and the Moon
You've probably seen the claim that every other planet in the solar system could fit in the gap between Earth and the Moon. Here it is drawn to a single consistent scale — both the planets and the gap itself. The Moon's distance isn't fixed, though, so try all three points in its orbit.
At the Moon's average distance (384,400 km center to center), this doesn't quite work. The seven other planets, lined up edge to edge, add up to about 380,010 km. Subtract Earth's and the Moon's own radii from the gap — since planets obviously can't overlap either one — and there's only about 376,292 km of clear space. Neptune ends up roughly 3,718 km, less than 1%, too big to fit.
The claim isn't simply wrong, though — it depends on where the Moon happens to be that day. The Moon's orbit isn't a perfect circle: at its closest (perigee, ~363,300 km) the planets fall well short, but at its farthest (apogee, ~405,500 km) there's about 17,000 km to spare, comfortably true. A "well known fact" that's actually a coin flip depending on the date is about as on-brand as it gets for this site.