That subsolar point moves as the earth rotates (of course) but also as the earth revolves around the sun - in January the southern hemisphere is tilted towards

That subsolar point moves as the earth rotates (of course) but also as the earth revolves around the sun - in January the southern hemisphere is tilted towards the sun; in July it’s the northern hemisphere (this is why seasons happen and why they’re opposed in the northern and southern hemispheres). The point itself is not marked on maps because it’s constantly moving, but the northernmost and southernmost limits are - that’s what the tropics are.