What is the definition of sunrise & set? Compare these for two people each on opposite sides of a tall hill!?

Question

Sunrise and sunset can be at very different times even for those in same time zone especially if a hill is in the way, people in a mtn shaded valley see sunrise much later than those on the sunrise side of the mtn and people on the west coast see sunset much later than those on the eastern side of a given mtn...so when is the real sunrise and real sunset ???

Answer 1

There's a bit more to it. The "flat horizon" idea is correct, and the calculation assumes that your view toward the horizon is unobstructed. But the calculation is also dependent on altitude, so Denver, for example, has a longer day (time between sunrise & sunset) than if it were at sea level.

If you're somewhere west of Denver looking at the Front Range up close, the sun will dip behind the mountains well before sunset. But sunset for your position, including altitude, is calculated as if the mountains weren't there at all. The horizon, for this purpose, is tangent to the earth, from ground level.

Next, sunrise occurs when the top of the sun first appears above the horizon, and sunset occurs when the top of the sun disappears below the horizon. It takes something like four minutes for the sun to rise or set, so that gives us four minutes of official daylight we wouldn't have if they used the middle of the sun, for example, as the yardstick.

Next, the sun's rays bend as they pass through the earth's atmosphere. This atmospheric refraction is greater as the sun rises and sets than at midday when the sun is high overhead. In the morning and evening, sunlight passes through more air because of the angles involved.

This means that when we see the sun's rays appear or disappear, the sun by that time is already below the horizon. The sunrise/sunset calculations take this refraction into account, so that gives a few more minutes of daylight.

Most of the time we pay no attention to these things, but twice a year, they're apparent if you pay attention. On the equinoxes, on the first day of spring and the first day of autumn, we're supposed to have twelve hours of daylight and twelve hours of darkness. Based on the sun's position, that's correct, but if you look at the published sunrise/sunset times for those days, you'll see that there's about 12 hours, 4 minutes of daylight, and 11 hours, 56 minutes of darkness.

This eight-minute difference (or maybe it's twelve minutes -- I forgot) is due to the difference between the solar position at equinox and the definition/calculation of sunrise/sunset, which includes the "transit time" of the sun and the atmospheric refraction.

Hope that answers your question satisfactorily,

Answer 2

Sunrise and sunset times can be calculated for any place on the planet in any time zone but they are determined presuming a flat horizon. Hills make a difference locally. Sunrise occurs when the top of the sun first appears above the horizon and sunset when the top drops below the horizon.

Answer 3

SUNRISE---is the time at which the first part of the Sun appears above the horizon in the east. Sunrise should not be confused with dawn, which is the (variously defined) point at which the sky begins to lighten, some time before the sun itself appears, ending twilight. Sunrise is not constant, it is different at different places on the globe.

SUNSET---the time at which the Sun disappears below the horizon in the west. It should not be confused with dusk, which is the point at which darkness falls, some time after the beginning of twilight when the Sun itself sets. Sunset is not constant, it is different at different places on the globe.

Answer 4

Sunrise is defined by latitude and altitude. Obviously somebody at the same latitude but higher up (ie altitude higher) will see sunrise earlier and sunset later than somebody lower down. Now what was your silly a ssed question again? gimme the best answer man, I need the points!

Answer 5

For me a poem has to have rhythm. It doesn't necessarily have to rhyme but it needs to hit my emotions. I think clarity of expression is important as well. I don't like to second guess what I'm reading about. I always look for what I term "poetic gems"in the text.

Answer 6

When YOU can no longer see the sun, it has set. When YOU can see the sun, it has risen. It is a completely subjective answer.