Keeping time at the planetarium, the garden is surrounded by a slotted circular wall. The tall slot in the image is north of the center of the circle, and during the meridian passage of the Sun it allows a shaft of light to fall on the ground outside the wall. The narrow slot and deep wall limit the time this happens to about 15 minutes, and within minutes of the true meridian passage the slot is exactly aligned with the Sun so that the sunlight illuminates the white stone at its interior base. The length of the shaft on the ground varies seasonally, reaching extremes that go beyond the curb cut at summer solstice to close completely with only a sliver of light at the winter solstice. The midpoint at the equinoxes is close to the curb. Since Louisville is toward the western border of the Eastern Time Zone, during daylight savings time the meridian passage -- local solar noon -- is at 1:49 for the summer solstice and 1:37 PM at the autumnal equinox. The time varies with the analemma due to the eccentricity of Earth's orbit.