Total Lunar Eclipse Tonight

Update: Here are some photos I took with a point-and-shoot Canon PowerShot A710 IS at 6x zoom with digital image stabilization. The photos are full-size, only cropped from the 7.1 MP originals.

The beginning of the eclipse is impressive, it really does look like there’s a bite taken out of the moon. During the partial eclipse, the curvature of the shadow just makes it look like a crescent moon. The prettiest was right before full eclipse, when most of the moon was reddish-orange, except for a white spot on the edge. The last one is a still from a video camera— the moon was too dark and I didn’t have a tripod.

22:46 HST       f/4.8       1/500 s

23:16 HST       f/4.8       1/200 s

video still

Lunar eclipses are perhaps the most common of celestial eclipses, but they still don’t happen every year in a given place. Tonight, one will be visible from Hawaii (Australia, N & S America as well), beginning just before midnight local time and lasting 1.5 hours. During the eclipse, the moon appears reddish because sunlight reflects through the earth’s atmosphere where blue light is absorbed, much like a sunset or sunrise. Before and after, the moon will be shaded by the penumbra and then partially eclipsed. Here is a link with more details about lunar eclipses.

Source: NASA

Sorry for the late notice…

Erratum

I was going to post yesterday about the second Lahaina Noon but it turns out I got the dates wrong. I finally found the Honolulu planetarium’s astronomical highlights, also known as ephemerides, for 2006. This year, instead of being on May 31st and July 12th, Lahaina noon happened a day earlier on May 30th and July 11th.

The dates for the solstices and equinoxes change up to a day from year-to-year, and Lahaina noon is directly related to those occurrances. In fact, I bet that on one day, the sun is a few hundredths of a degree south of the zenith at solar noon, and the next day it is a few hundredths of a degree north, and Lahaina Noon is just whichever day it is closest. By extension, for each given latitude, there must be one spot around the earth that experiences the exact Lahaina noon. Or for a given longitude, you could travel north or south a few hundredths of a degree to get the sun exactly overhead. I’ll have to research this some more.

As a side note, I keep calling it the Honolulu Planetarium, but its real name is the Jhamandas Watumull Planetarium at the Bishop Museum.

Lahaina Noon +2

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.

Lahaina Noon Today

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.