Why Northeast and Northwest Instead of Just East and West?
On the equinoxes—March 19, 20, or 21 and September 21, 22, or 23, depending on the year—the sun rises due east and sets due west. However, because of the tilt of the earth on its axis, from the spring equinox in March until the summer solstice on June 21—give or take a day depending on the year—the sunrise swings farther and farther to the northeast each morning, and the sunset swings farther and farther northwest. After the summer solstice, the sunrises and sunsets move slowly back toward due east and west each day until they’re exactly east and west again on the autumnal equinox in September.
In autumn, the sun makes the same shifts for its sunrise and sunset to the southeast and southwest until December 21, the winter solstice, give or take a day—not that most of you will likely have many vegetables in your garden then unless you live in Texas, Florida, or another far southern state.
The change in the sunrise and sunset locations depends entirely on the tilt of the earth’s axis. Were the earth’s axis not tilted, the sun would rise due east all year.
The earth’s axis is tilted, however, giving us our seasons and changes in the locations of sunrise and sunset throughout the year.
Spring (Vernal) Equinox
On the spring equinox, the earth’s axis (shown here with the north pole tilted away from the observer) is tilted neither toward nor away from the sun. For a moment, it is, instead, at a perfect 90º angle to the sun’s rays, causing equal day and night length and the sun to rise due east and set due west.
Summer Solstice
Starting the moment after the spring equinox and lasting up to its peak at the summer solstice, the northern hemisphere is increasingly tilted toward the sun, causing longer and longer days and the sun to rise progressively toward the northeast and set crescively toward the northwest.
The lowest of the above diagrams does not depict the actual relationship of the earth’s tilt to the sun in the summer (in the north). Instead, it’s meant to help you to picture where the sun would rise were you standing in North America during the summer.
Fall (Autumnal) Equinox
On the fall equinox, the earth’s axis (shown here with the north pole tilted toward the observer) is again tilted neither toward nor away from the sun. It is instead again at a perfect 90º angle to the sun’s rays, causing equal day and night length and the sun to rise in the due east and set in the due west.
The lowest of the above diagrams does not depict the actual relationship of the earth’s tilt to the sun on the autumnal equinox. Instead, it’s meant to help you to picture where the sun would rise on that day.
Winter Solstice
On the winter solstice, the earth’s axis is tilted away from the sun, causing shorter days in the northern hemisphere and the sun to rise in the southeast and set in the southwest.
The lowest of the above diagrams does not depict the actual relationship of the earth’s tilt to the sun in the winter (in the north). Instead, it’s meant for you to picture where the sun would rise were you standing in North America during the winter.
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