Lahaina noon is the Hawaiian term for the moment of high solar noon when the sun is directly overhead. In this moment shadows of vertical objects seem to disappear since the sun is not at an angle.
For the Tropic of Cancer or Tropic of Capricorn the local Lahaina noon is on the respective summer equinox. But for all latitudes in between there are two dates during the year in which a local Lahaina noon occurs.
Since I live in the tropical Caribbean my question is how can I calculate the date and time when local Lahaina noon will occur? If it matters my local latitude is 19.3° N (19° 20’N).
My Google Fu is weak on this one since I am only find information about locations in Hawaii, and no means of making the calculation.
You can quickly look up that sort of thing in the Nautical Almanac, or of course use computer software or a website calculator. It should next occur around July 26. The exact time of local noon naturally depends on your longitude.
I saw mention of Laihaina noon on some internet blurb recently and it occurred to me that I’ve never bothered to take noticie of the phenomenon in all the years I’ve lived in the tropics. Some back of the napkin calculations got me to thinking this must be coming soon for my location. Thought I’d try to take some pics this time to show the family.
The day on which the sun is closest to being directly overhead is the day (or days) at which the declination of the sun is equal to your latitude. Using the less accurate approximation on the Wikipedia page, along with your latitude of 19.3° N, I find that the dates are either 147 or 248 days after the winter solstice. This would make it either May 17 or July 27.
Incidentally, the name “Lahaina” might be Hawaiian, but the concept is recognized throughout the tropics, and those dates are often the most important ones on local calendars (instead of the solstices, as is typical in temperate areas). I recall reading of a Mayan community that had their two main religious festivals on their Lahiana days. When the missionaries came in and converted them to Catholicism, they found that the locals seemed to have a particular affinity for two saints. It turned out that those two saints were the ones who had their feast days on those two days, so they could keep their celebrations.
You don’t need to be too accurate, but the approximation you used is too crude, then. I did no calculations, just opened up the almanac to the appropriate days. Noon in the Caribbean will be around 16 or 17 Universal time, at which the declination of the Sun will be/was:
2017 May 16: 19° 15’
May 17: 19° 28’
July 26: 19° 17'
27: 19° 3'
So look for those short shadows on July 26. Factor in your time zone and longitude to calculate the instant of high noon.
Interesting point: Eratosthenes’ calculation was pretty good, especially considering how much imprecision there was in measuring the distance of the baseline. Columbus knew the world was round but had calculated a much smaller diameter. (There might have been some self-serving thinking on his and the Spanish’s parts)
He bumped into land pretty much when he thought he would, he just didn’t know there was a continent and a rather large ocean to go before reaching China.
I still think that it wasn’t coincidence that Columbus found land where he expected it. I think that he had privileged knowledge from northern fishermen who knew there was land there, and then went looking for justifications for his knowledge that he could present to others. His mistake was just in the identity of the land, not its presence.
For the time, note that Lahaina’s longitude is about 27 sun-minutes west of the 150th meridian, which is the baseline for the Hawaii-Aleutian time zone. The Equation of Time is about minus 4 minutes in mid-May and plus-7 minutes in late July. So you’ll have vertical Sun at 12:23 PM on May 16 and 12:34 PM on July 26.