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I would think though that the Hawaii sun in October won't be too strong outside the hours of 10 and 2, especially in October when days are less than 12 hours long
But here's a factor nearly everyone misses... it's not just the highest angle the sun reaches in the sky... the closer you are to the equator the quicker the sun rises to a high angle, and the more hours out of the day it stays high in the sky. In other words there are more hours out of the day when the sun is high, and at its most intense in Hawai'i than in Boston.
Another factor anytime is that the sand in Hawai'i is very reflective, bouncing 25% of the burning UV rays around.
I have a good friend with very fair skin, and at the beach she can burn quite quickly at 4 in the afternoon, while sitting in shade, if she doesn't put on her sunscreen.
As for the sun rising fast, it's still not as many high angle sun hours as summer in Boston on a clear day
In fact, the closer you are to the equator, the faster the sun climbs and dips before and after noon just as it rises and sets fast
And on the equator on the equinox, the sun dips and rises equally as fast no matter what time of day it is
Where as father from the equator the fastest drops and rises as a percent of total is closer to the 6 o'clock hour
Hawaii does get fast sunrises and sunsets, but the peaks of noon are also quicker duration
And currently on today's date, you will see how much the sun drops from solar noon into the hour after solar noon. It drops by like 10 degrees of altitude. Where as Boston though solar noon is no where near as high, the drop an hour later isn't even half of 10 degrees of altitude
Location: not sure, but there's a hell of a lot of water around here!
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Quote:
Originally Posted by EricS39
The volcanic black sand must be a big part of it.
Yea, sure, that's it.. Go to the beach that isn't 'volcanic black sand', at 10 in the morning, without sunscreen, and lie there for an hour or two. See how that works out for ya.
No, I was talking about the white coral sand found on most Hawaiian beaches. It's highly reflective.
Quote:
Originally Posted by whtviper1
You are hugely confusing hours of daylight due to the tilt of the earth versus how high overhead the sun actually gets.
Yes, this is exactly the point I was trying to make to the OP.
The single biggest factor affecting the intensity of the UV rays that tan us and burn us is the angle from the horizon, with 90 degrees being the maximum, because that's when those rays have the shortest distance to travel through the atmosphere. At lower angles in the sky the distance to the surface is longer, and the more UV that is filtered out.
But here's another way of explaining it which may communicate better...
Quote:
The tropics burn, and they burn bad, and they burn year-round, and they burn for relatively more hours per day than places in the high latitudes like the USA's northern States or Northern Europe.
.....
In calculating your risk of sunburn/suntan on a clear, sunny day, the season of the year, your latitude, and most other factors can be essentially forgotten---- except your two types of altitude: (i.e., the sun's altitude above the horizon, and your altitude above sea level)
1. The sun's altitude in the sky above the horizon line..... If the sun is below a certain level, you aren't at risk even in Hawaii or Los Angeles. If it is above a certain level, you are at risk. In the tropics, even in mid-winter, the sun rises to high altitudes year-round. As an example, I chose Quito, Equador, which is essentially right on the equator (zero degrees latitude)..... Even at winter solistice (Dec. 21) the sun rises at noon to 67 degrees high in the sky, which is higher than it gets even on the summer solistice in places like Seattle, Washington or London, England. Thus, the UVB is as strong on Dec. 21 on the equator as it is on June 21st. at such northern cities!
2. Worse yet, due to the celestial mechanics of the Earth/Sun in space, the way the sun transits the sky in the tropics leads to addtional UVB danger. In Quito, on Dec. 21, the sun rises very rapidly in the morning to high enough altitude to be dangerous, reaching 30 degrees high by 8:30 am, and staying higher than that all day, all the way until about 3:45 p.m.
1. The sun's altitude in the sky above the horizon line..... If the sun is below a certain level, you aren't at risk even in Hawaii or Los Angeles. If it is above a certain level, you are at risk. In the tropics, even in mid-winter, the sun rises to high altitudes year-round. As an example, I chose Quito, Equador, which is essentially right on the equator (zero degrees latitude)..... Even at winter solistice (Dec. 21) the sun rises at noon to 67 degrees high in the sky, which is higher than it gets even on the summer solistice in places like Seattle, Washington or London, England. Thus, the UVB is as strong on Dec. 21 on the equator as it is on June 21st. at such northern cities!
In case anyone wants the math.....
0 (equator) - (-23) (Tropic of Capricorn). = 23. 90 (vertical angle) - 23 = 67 degree sun angle.
The beauty about sun angle, it is one of the easiest geometry equations out there - no wacky cosines, sines, or tangents (no trig)
Last edited by whtviper1; 07-22-2014 at 02:53 AM..
1. The sun's altitude in the sky above the horizon line..... If the sun is below a certain level, you aren't at risk even in Hawaii or Los Angeles. If it is above a certain level, you are at risk. In the tropics, even in mid-winter, the sun rises to high altitudes year-round. As an example, I chose Quito, Equador, which is essentially right on the equator (zero degrees latitude)..... Even at winter solistice (Dec. 21) the sun rises at noon to 67 degrees high in the sky, which is higher than it gets even on the summer solistice in places like Seattle, Washington or London, England. Thus, the UVB is as strong on Dec. 21 on the equator as it is on June 21st. at such northern cities!
In case anyone wants the math.....
0 (equator) - (-23) (Tropic of Capricorn). = 23. 90 (vertical angle) - 23 = 67 degree sun angle.
The beauty about sun angle, it is one of the easiest geometry equations out there - no wacky cosines, sines, or tangents (no trig)
In winter solstice when the sun reaches 67 degrees high on the equator line, you need to subtract for Honolulu the additional 21.3 from it
That's only about 45 degrees up
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