Inspired by the equinox that's coming in about seven hours: Higher latitudes get less insolation (watts of sunlight per square meter of level surface area averaged over a year) than lower latitudes. How high would the Earth's obliquity (axial tilt) have to be for the poles to get more insolation than the equator? Or could this never happen? Assuming Earth's orbit was perfectly circular and that the insolation is exactly 1 kilowatt per square meter when the sun is directly overhead, is there a simple formula for insolation as a function of latitude and obliquity?