Facts of the Matter: Each sunrise may be unique, but sun’s path remains same

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The sun has a shallower angle at more northerly latitudes, extending twilight. Above, the sky glowed an hour before sunrise Thursday in Frankfurt, Germany. At left, the sun rises in the east and sets in the west because Earth rotates around the sun from west to east. To better visualize this, imagine you are seated in the middle of a crystal sphere with the sun, moon, stars and planets rotating around you.

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A word from Captain Obvious: The sun rises in the east and sets in the west.

We learn this early, but does it register in daily life? I see many TV programs that illustrate the rising or setting of the sun backward. It is as if they could not find a good sunrise shot, so they used a sunset and ran it backward.

Who would notice, right? Let’s look at the details.

The farther north or south from the equator, the more of an angle the motion of the sun forms with the horizon.

The angle at which the sun moves at sunset and sunrise is a direct effect of the latitude. It is always equal to 90 minus the latitude, thus, 90 degrees at the equator, zero degrees at the pole.

At the North Pole the sun moves parallel to the horizon but always moves counterclockwise from east to west.

In Honolulu, latitude 21.5 degrees, the angle is 68.5 degrees. This steep angle in the tropics is responsible for the shortness of dawn and dusk. At higher latitudes the sun’s shallower angle means that it takes more time to disappear below the horizon, so the twilight lingers longer.

At the equator, zero degrees latitude, the sun rises and sets “straight up” perpendicular to the horizon, which equals 90 degrees. There the backward sunrise/sunset movie will work just fine.

In the Northern Hemisphere, north of the Tropic of Cancer at 23.5 degrees latitude, the sun spends most of its time in the south. In that tropic zone it can be in the north for a short time around noon.

In the days between the March and September equinoxes, it rises and sets in the northeast and southeast respectively but spends most of the time in the southern sky.

Regardless, it moves counterclockwise, that is from left to right as we follow its path throughout the day, even at the equator. Accordingly, it will always move from left to right along the horizon at sunrise and sunset except at the equator.

We retained the left-handed clockwise motion (curled fingers) from the movement of the shadow on a sundial, which was the earliest numbered version of a clock.

In the Southern Hemisphere all of the motions are a mirror image as the seasons are reversed: The sun is mostly in the north, moves clockwise from right to left, etc. No matter what or when, it always rises in the east and sets in the west, in the southeast and southwest in the days between the September and March equinoxes.

Of course, all of this refers to the apparent motion of the sun in the sky. In actuality, Earth rotates from west to east (despite what the flat-Earthers claim). It can be difficult to visualize this. What makes it easier is to imagine sitting in the center of a crystal sphere sky with the sun, moon, planets and stars stuck on it as it rotates above.

That is what our ancestors did and modern astronomers still do as a model to observe the celestial motions.

Richard Brill is a professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.