IF it's flat (solved)

well here you go: 

establish: 

this is the case -- search/examine "Polaris star trails" & you'll find plenty of reliable data -- PLENTY [enough; it does that]

observe:

there is a "midnight sun" / 24-hour visible sun for months straight WAY NORTH [Arctic Circle]

take that in...

in a Heliocentric Model, this requires an almost full-tilt Earth to point at the Sun & get that effect

now remember, Polaris is stationed there [90º vertical from North] since time immemorial -- mariners + navigation, etc.

LOTS & LOTSA HISTORY OF POLARIS/NORTH STAR [specifically a star mind you]

how does one get a 24-hour sun WHILE witnessing Polaris circular star-trails [daily those are]

this is impossible

practice:
find any two objects & hold them in each hand

now to try simulate the Heliocentric 'orbit' WHILE accounting for Polaris/North star... TRY TO THROW IN THAT WOBBLE

this should do it...

for extra/bonus funzies:
try to imagine Polaris/the constellations moving about the sky along w/ Earth to account for what we witness along w/ the Heliocentric model

i'll remind:

it's flat