When is sun setting

Its first printed appearance, in Venice in , was based on a mediaeval Latin translation of the Arabic adaptation of the original Greek — quite a multicultural achievement! The sunset direction reaches its northerly and southerly extremes at the solstices, while the noon altitudes are also at their extremes highest and lowest at the solstices. The midpoints in both cases occur at the equinoxes. Thanks largely to Hipparchus of Nicaea — who worked about BCE, and to whom Ptolemy was indebted — astronomers had already figured out the geometrical configuration of the equinoxes.

You can get the idea by visualising a third, more obvious plane — an extension of the one we appear to be standing on, bounded by the horizon with the sky sitting on top like a hemispherical dome. This is the plane in which the sun appears to make its daily journey about Earth, from sunrise to sunset and on through the night until sunrise again.

It must have seemed strange to the ancients that the sun had two different paths in its journey about the Earth. Still, these astronomers had figured out that these two paths lay in two different, intersecting planes. The equinoxes and the directions of sunset show why. The equinoxes occur when the sun sets due west, and the days and nights are virtually of equal length everywhere on Earth.

So, in its yearly journey along the ecliptic, there are only two days when the sun crosses the equator. Every day after that, the Sun rises a tiny bit further south. At the fall equinox, the Sun rises due east and sets due west. It continues on it's journey southward until, at the winter solstice, the Sun rises are far to the south as it ever does, and sets as far to the southwest.

Many, if not most, prehistoric cultures tracked these rising and settings points with great detail. If they had jagged mountains along the horizon, the exact points could be readily remembered. Without a suitably interesting horizon, standing stones could be arranged to line up with the various rising and setting points.

Or, tree poles could replace the standing stones. Or, rock cairns could be used. How does this work? Figure 8 and 8a show the apparent paths of the Sun as seen from Hawai'i, the southernmost State of the United States, 21 degrees north of the equator. The paths are all parallel to each other, but are slanting at 21 degrees to the horizon. It will also be noticed that the horizon divides the total path of the Sun into equal periods only on the first days of spring and fall, i.

In summer, the portion of the Sun's path above the horizon is much greater than the night portion, and the reverse is true in the winter. As the Earth rotates, different locations on Earth pass through the sun's light. The animation shows how that looks hour by hour for 4 hours. As your town turns toward the sun and begins to enter its light, the sun seems to rise in the east. As your town begins to leave the sun's light and enter darkness, it appears to set in the west.

Try this!