astronomy

Climax shadow

In addition to land and water, some globes are printed with a kind of map that looks like a skinny numeral 8. This is called the analemma, and it charts the apparent path of the sun up and down and across the sky as the seasons change. For the northern hemisphere, the analemma teaches you that in summer there’s a lot of sun and it soars high toward the north.

One more marking, right around the middle of the globe, shows a belt of latitudes called the tropics, bounded north of the Equator by the Tropic of Cancer and south of the Equator by the Tropic of Capricorn. The word “tropic” means “turning point,” and it’s at the two tropics where the sun changes its course along the analemma: from northbound to southbound when it’s directly overhead at the Tropic of Cancer on the first day of northern summer, and back again from south to north when it’s directly overhead at the Tropic of Capricorn on the first day of southern summer.

So in the tropics, and only in the tropics, there are two days in the year when the sun at noon will be directly overhead on its way up to and then back down from its boundary tropic. On those days, at the brief moment when the sun is at the zenith, a vertical object’s summer-short shadow will dwindle all the way down to nothing. In Hawaii, America’s only tropical state, the first of those days is always in May and the second is always in July. For today, May 26, 2022, the celestial event in Honolulu was this.

The moment of zero shadow is called the zenith passage or (specifically in Hawaii) Lahaina noon. Before that moment this month, the sun where I recorded this composite image was a little clouded over and the shadow of the boom on the pole wasn’t intense enough to be educational, but you’ve now seen the teaching aids from just at and then just after the climax. Notice how the invisible shadow of the speed limit sign becomes visible again as Hawaii’s sky swings back to ordinary. You were looking northeast.

To time the shadow, the preferred chronometer will be Frances Cornford’s (1886-1960) mood watch. It goes tock tick, not tick tock, and you see that that’s the correct right-to-left astronomical order.

I wakened on my hot, hard bed;
Upon the pillow lay my head;
Beneath the pillow I could hear
My little watch was ticking clear.
I thought the throbbing of it went
Like my continual discontent,
I thought it said in every tick:
I am so sick, so sick, so sick;
O death, come quick, come quick, come quick,
Come quick, come quick, come quick, come quick.

Morphology and evolution of the gnomon

The sententious fragment: In the tropics — that is, in the latitudes between the Tropic of Cancer and the Tropic of Capricorn — there are two moments in the course of the year when the sun passes directly overhead and an object won’t cast a shadow longer or wider than itself. The first of these occurs when the sun is on its way north to the Tropic of Cancer, which it will reach on the summer solstice; the second occurs when the sun is on its way back south to the Tropic of Capricorn, which it will reach on the winter solstice. For 2021, the first moment in tropical Honolulu was on May 26 at about 12:29.

The whole:

 

 

Restored, perhaps rightfully

The legacy of the Amherst College astronomer David Peck Todd (1855-1939) has been pity and derision. Astronomers know him as the but-for-the-grace-of-God colleague who almost but not quite discovered the moons of Mars and was defeated by cloud cover every single time he tried to observe a solar eclipse. Readers of poetry know him as the husband of Mabel Loomis Todd, Emily Dickinson’s first editor, who betrayed him with Dickinson’s brother. Julie Dobrow sums up the sad story at

http://www.juliedobrow.com/uncategorized/david-peck-todd-birthday/

In 1924, briefly released from the mental hospital where he spent his last years, David showed up in Washington and attempted to make radio contact with the Martians. I tell that sad story at

https://jonathanmorse.blog/2015/06/12/asks-air-silence-seeks-sign/

But he posed on the occasion in the observatory at Georgetown, and some photographs survive on the record in the Library of Congress. I observe one.

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“Dr. David Todd, Georgetown Observatory, 8/21/24.” National Photo Company Collection, Library of Congress, https://www.loc.gov/pictures/collection/npco/item/2016838239/.

Doesn’t the man in this image deserve to survive as he would have liked to be remembered — smiling and competent, at the controls in chiaroscuro and beautifully shined shoes? In hope for him and for us all, I photoshop.

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Some history on behalf of the Thirty Meter Telescope

Here, dating from 1854, is a view of downtown Honolulu.

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Here’s a detail from the lower right of the image.

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And here’s a double description of what your eyes have just beheld. One half of the description comes from the 1847 second edition of Herman Melville’s first book, Typee; the other half comes from an 1835 translation of what appears to have been Melville’s source, an 1834 account of an expedition around the world by the German botanist F. J. F. Meyen.

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And here are two more pages of Meyen which Melville didn’t use.

The_Foreign_Quarterly_Review.pdf

As I write, a group of Hawaiian monarchist protesters are holding up construction of the great Thirty Meter Telescope atop the Big Island’s Mauna Kea. They call themselves cultural practitioners, and what they claim to be practicing is the animist religion of pre-contact Hawaii. In this they are supported with money and public relations by Kamehameha Schools / Bishop Estate, the combined successor power of Hawaii’s nineteenth-century puppet kings and their Christian missionary puppeteers.

Typee is partially non-fiction, partially fiction. For a start, Melville’s “four months’ residence” in the Marquesas was only three weeks. As Hawaii’s history is generally taught, it too is partially fiction. But look at that illustration again. Look at that woman with her parasol and her Hawaiian slave.

It tells you that the things called history and culture are complicated, but sometimes they show us things that are true. So please: before you click away, look one more time at the man towing his missionary burden. He wasn’t a king or a priest. None of the people blocking progress on Mauna Kea today would claim descent from him. Still, he did exist, and perhaps he’s worth trying to remember.

Still image series: zenith passage, Honolulu, May 27, 2019

It happens only in the tropics — that is, the latitudes between the Tropic of Cancer and the Tropic of Capricorn. Twice a year there — first when the sun is on its way north to the Tropic of Cancer, which it will reach at the summer solstice, then when it is on its way  back south to the Tropic of Capricorn, which it will reach at the winter solstice — the sun at noon reaches a point directly overhead and a vertical object will cast no shadow. In Hawaii, where I live, the two dates will be in May and July. And the word tropic means turning point.

Today on Oahu, the still point (terms zenith passage or Lahaina noon) was predicted for 12:28, plus or minus a few minutes on different parts of the island. I set up my vertical object at 9:00 in brilliant sun and started shooting. The brilliant sun persisted until just about noon, but then the clouds rolled in. However, with the camera facing approximately north:

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Feel free to copy, but please credit me.