I've been puzzling over the question of how the MC solar system works to explain certain oddities such as:

• Day and night are always equal length
• There are no seasons
• The moon and sun are always opposite each other
• The moon still has phases despite being locked opposite the sun
• The moon and sun appear square
• The time is the same everywhere in the world
• There are no solar or lunar eclipses
• The arrangement of stars in the sky doesn't change as time goes on
• The dark portion of the moon (when it isn't full) is visible as something solid and black, with a grey border

I couldn't work out anything that accounts for all the bullet points, but I worked out something that's a closer match than the standard heliocentric solar system. Feel free to suggest modifications.

The earth is flat. Not a cube, just flat (looks like the flat-earthers are right. But only in Minecraft). There is no sharp corner like on a cube, but the world doesn't loop around like a sphere. The world is a flat square with a transparent wall around it (the world barrier). The world extends past the barrier, but not far (far enough you can't see the edge from within the barrier).

The earth doesn't go around the sun. The sun doesn't go around the earth either, they are both fixed in place (this will make sense in a moment).

The moon is also fixed in place, on the opposite end of the earth from the sun. The moon and sun always appear opposite each other because they physically are.

The moon is a cylinder with equal height and diameter, oriented so it appears as a square from the earth. The moon rotates about an axis through the circular ends. Slightly less than 1/2 the cylinder is black. This means that as the moon rotates, there appears to be phases from earth because you see part of the moon which is black. It is still illuminated, it's just black. Because it is slightly less than 1/2, during a new moon you see a grey/white border around it.

The earth rotates about an axis perpendicular to a line from the moon to the sun (passing through the earth), and the axis is placed so that the disk rotates to sometimes be facing towards the moon, sometimes the sun, sometimes perpendicular to both of the them so you see both at once on the horizon, and this creates the day/night cycle.

This allows for a lot of the perceived oddities of the MC solar system (bulleted above), but does not account for being able to see the sun and moon on the horizon if the closest obstruction is far away (this would be partially solved by a spherical earth, but that breaks everything else). It also doesn't explain biomes (why is this random region cold when it's surrounded by jungle for example?).