content: The moon is at most 30-ish Earth diameters away from Earth when viewed edge-on (well, when viewed from any location) or about 110 Lunar diameters.  This picture shows the gap is well within that distance. However Every 14-ish days, the moon will be on the opposite side of the Earth, at the same angular distance.  That is, angle Earth-Mars-Luna will be the same every fortnight. As the moon passes on the Mars side of Earth, it will be closer to Mars, and if my math is correct, it will appear to be 0.00005°- appx .22 arc-seconds larger than when it is behind.  This is roughly the angular distance the hour hand on a clock moves in one second. You are correct that the moon will appear larger when it is on the Mars-side and smaller when it is on the opposite side, but it is roughly equivalent to the difference in size between a penny and a dime when viewed from roughly 500 feet. Disclaimer - these are rough numbers, but the scale is close enough.  The difference between a penny and a dime from 500 feet is about the same as the difference between a penny and a dime from 494.6114 feet. Edit - Hour hand moves .00833 degrees, 30 arc-seconds per seconds.  So roughly 136 times farther than I stated above. Edit 2.0 Electric Boogaloo: Earth - to - Mars = 33.9 million miles Earth - to - Moon = 238,900 miles Moon on Mars side of Earth = 33.6611 million miles Moon on opposite side of Earth = 34.1389 million miles Moon diameter = 2158 miles, 1079 miles radius arctan (1079 miles / 33.6611 million miles) = 0.00183757° ... X 2 for an included angle of .00367514 degrees.  That is the angular size of the moon as seen from Mars when the moon is at its closest possible point. arctan (1079 / 341389) = 0.00181185° ... X 2 = 0.0036237 degrees when the moon is farthest away when the Earth is closest. For a net difference of 0.00005144 degrees, or .185184 arc-seconds.  My initial numbers were a little high. For the dime / penny comparison, they would need to be 25061.334309 inches, or 4.7464 miles, away, to have the same difference in apparent size ( (.375 - .3525) / sin (0.00005144) ) If you could zoom in enough to view them actual size from nearly 4-3/4 miles away, then you could definitely see the difference in size. But - at only 0.045" difference in diameter, you would absolutely have to zoom in to where they were 50% of actual size in order to see the difference. (Which is why arc-seconds are used for apparent sizes.) Likewise, it would require zooming in to the Earth/Moon picture until they were 50% actual size in order to see the difference as well.  My monitor won't display that.