Sunrise, Sunset ?

[ketch]

This is an opportunity for someone to show off geekness. My experience and thoughts say that the sun rises earlier and sets later when your at altitude. I've never actually checked. Anybody know how much effect altitude has?

[iain]

That would make sense since your horizon is farther away than at lower altitudes. If you were infinitely low to the ground your horizon would be right at your nose.

[iain]

sunrise is 1 minute earlier for every 1.5km of altitude.

[Dru]

please show proof that the relationship is linear and invariant with season and latitude

[iain]

well it is linear because it is basic trig, but I don't know about the season/latitude stuff

[Dru]

if its basic trig let's see your proof.

[Alex_Mineev]

The function is tangent based, not sure about the exact formula. Time delta increases like 1:1 with increase of altitude in the beginning but when time delta closes to 6 hours altitute grows infinitely.

[iain]

 

QED

[scott_harpell]

if its basic trig let's see your proof.

 

Battle of the Nerds!!!

[Dru]

The function is tangent based, not sure about the exact formula. Time delta increases like 1:1 with increase of altitude in the beginning but when time delta closes to 6 hours altitute grows infinitely.

 

ding ding we have a winner - for mountains at the equator, during equinoxes only. which uber geek will come up with the seasonal function for mountains at any latitude??

[olyclimber]

Let's talk math.

[Norman_Clyde]

According to James Kaler's "The Ever Changing Sky":

"Horizon dip [this is the actual term], measured in minutes of arc, is equal to 1.811 times the square root of the elevation in meters or, by coincidence, very nearly equal to the square root of elevation in feet."

 

Translating minutes of arc into seconds of actual time is very complicated, as it depends on the latitude of the observer and the current declination of the sun. One degree of movement, 60 minutes of arc, takes 4 minutes, but then you have to factor in the angle at which the sun is dipping below the horizon.

 

But altitude does make a difference. To quote the same book: "The effect of horizon dip can be quite significant and noticeable. Even for a 2-meter tall person at the shore, the dip is over 2' [2 minutes of arc] and the delay in a vertical sunset (zero degrees latitude) is 10 seconds. At an elevation of 800 meters, the dip increases to 51 [minutes of arc]."

 

In other words, if you happen to be on the equator, 1024 feet of elevation gives you 32 minutes of arc, or just over 2 extra minutes of visible sun (at each end of the day).

 

Dru, it's still only at the equator, but do I get runner-up?

Edited May 25, 2004 by Norman_Clyde

[Dru]

ya olyclimber wins and norman comes in second. iain is routed! back to fake spock ears iain you pseudo-geek