A Kauai Blog

A reader suggested a followup to my Lahaina noon photos, and since I’m always game for a backyard science observation, here are similar pictures taken at the solar noon (12:35pm) today, two days after the Lahaina noon. You can see the shadows are no longer straight down, and from all my reading on the subject, I know they are pointing due south at that moment. Incidentally, this proves the earth is round…

Be sure to mouse-over the photos on my blog because I often put some explanations in the pop-up text.

I just noticed that the EXIF dates on all my Lahaina noon photos are false because I’ve been using an old camera whose internal clock batteries are worn out.

This is the inaugural post for the “ephemerides” category:

Update: I was off by a day, Lahaina noon was May 30th this year. See my erratum.

Today at local noon (12:35 pm on the east coast of Kaua’i), the sun will be directly overhead, at a point properly called the zenith. It is commonly said the sun will cast no shadow, but in fact will cast shadows straight down and only perfectly vertical objects such as flag poles will have no shadow.

It turns out there was no scientific term for this occurence, and so the Honolulu Planetarium held a contest in 90’s and the name Lahaina Noon was chosen. Lahaina is a town on the dry south-facing coast of Maui where the sun is glaring, intense, and hot—the name itself means “cruel sun” (not to be confused with “mean sun“).

Source: NASA, graphic by the aptly named David P. Stern (“star” in German)

The path of the sun across the sky is called the ecliptic and defines an ecliptic plane. The angle of the ecliptic plane is constant for a given location, but it “moves” north and south with the seasons. On the imaginary line of the tropic of Cancer, 23°30′ of latitude north, the ecliptic touches the zenith once per year on the day of the summer solstice. Further south, the ecliptic passes north of the zenith and the sun will shine from the north the whole day. Lying between 21°54’N and 22°14’N, Kaua’i sees Lahaina noon twice, on May 31st and July 12th. Note that the other inhabited Hawaiian islands are further south and therefore experience the first Lahaina noon earlier and the second later, giving them more days of northern sunshine.

For the foreign readers, Lahaina Noon is also an pun on the expression high noon which denotes solar noon, when the sun is highest and hottest in the sky. Hawaii is the only US state in the tropics and thus the only one where Lahaina Noon occurs. I suppose billions of people live in the tropics around the world and don’t find the event special enough to name it.

Update: here are my photos of vertical objects at today’s Lahaina Noon.