So some people will not like that I am using the zodiac in this experiment because of its ties to astrology. Anyway ancient peoples saw constellations in the sky as a way to categorize stars. They called twelve constellations that appear over the equator at the spring and autumn equinox, the zodiac. The sun and the moon are always in one of the signs of the zodiac all the time. Go out and look and see it is true.
So the sun is in Pisces at the spring equinox (Mar 21) north spring that is. It then moves to the next sign of the zodiac a month at a time (on average because the constellations are not all exactly the same size). So it moves into Aries and then Taurus etc. On Sep 21 when all the zodiac constellations and the sun and the moon are all directly above the equator at all locations, the sun is moving from Leo into Virgo.
In June it is in Taurus and on Dec 21 it is in Sagittarius. We can all see this (well you can see what constellation is coming up just before dawn so you know what constellation the sun is in).
So we all agree that the sun follows the tropic of Cancer on June 21 and it follows the Tropic of Capricorn on Dec 21. Since the sun and moon are always in one of the signs of the zodiac (or rather they follow the line through the constellations that make up the zodiac), Taurus is directly overhead at noon on June 21 if you live on the Tropic of Cancer. (and you can actually verify this on those rare solar eclipse opportunities). Sagittarius is directly overhead at midnight for people that live on the Tropic of Capricorn. Easy to verify this one since it is dark and you can just look straight up. Taurus is directly overhead at midnight for people who live on the Tropic of Capricorn on Dec 21. Look up and see it.
So we have the sun following the tropic of Cancer at the summer solstice, Tropic of Capricorn at the winter solstice (opposite seasons for the southern hemispher). The sun follows the equator at the equinoxes (is that a word?). The signs of the zodiac that the sun is in follow it between the two Tropics. The signs of the zodiac that are 6 signs away follow the opposite routine between Cancer and Capricorn. If you live on the equator, Pisces will be directly overhead at 6 am and Virgo will be directly overhead at 6 pm on June 21.
So there are elaborate paths taken by the sun and the constellations that follow a yearly cycle. The zodiac constellations move back and forth between the two Tropics like the sun and travel across the sky at almost the same speed as the sun. It takes a month for the sun to catch up to the constellation. Okay. I think we can all agree that this is complicated but can be explained by some annual expansion or contraction of the path of the sun.
What about the moon? What does it do? Just go outside and watch it for a month. At this time of year, the full moon is over the tropic of Cancer at midnight. As the phases change it moves closer to the sun so that the new moon is over the tropic of Capricorn. For some reason the sun and the moon are always in one of the zodiac signs. The sun oscillates between the tropics of Cancer and Capricorn slowly over the year. The constellations of the zodiac are overhead between the two tropics and the equator depending on the time of day. The moon shuffles between the two tropics on a roughly monthly basis. Go out at the next full moon at see how high it is in the north and low in the south, the opposite of the sun. See how the near new moon is the opposite. Watch this for a year. Everyone here can do this.