Since most people know more about astrology than astronomy (and, no, they’re not the same thing), this nonsense has been making the rounds on Facebook recently. Needless to say (at least to anyone who paid attention in junior high school science class), Mars will not appear to be as big as the Moon.
The absolute closest distance the Earth and Mars can theoretically ever come to each other is 33.9 million miles. We’ve never observed that, due to the elliptical nature of the orbits of planets. An approach that close requires a coincidental alignment of orbits that is exceedingly rare. So rare, that it’s not been observed in human history.
For comparison, the orbits of Venus and the Earth can come within 24 million miles of each other. The diameter of Venus is 3,032 miles, while Mars is 4,212 (not much difference in the grand scheme of planets). Earth’s diameter is 7,918 miles. (give or take. It’s a bit more at the equator, less at the poles, due to the spin of the planet on it’s axis.) Venus, even at it’s closest approach, 10 million miles closer than Mars ever gets, never appears as more than a bright star in the morning or evening sky, so the idea that Mars will look like our Moon is, simply, hooey. Never going to happen.
If you ever do see something in the sky as big as the Moon (that’s not the Moon), we’re in deep shit. That’s either the Death Star, or Gallifrey.
Either one of those, and we’re screwed.