Friday, December 21, 2012

Winter Solstice

Happy winter solstice! Here in the Northern Hemisphere, I've always felt that the winter solstice and the coming lengthening of days is worth celebrating. As winter begins here, this will be the shortest day, and while it will be cold in the coming months, there will be more light.

Tyrrhenian Sea and Solstice Sky Credit & Copyright: Danilo Pivato, Source: via minouette on Pinterest

The length of days varies little at the equator, and in the high arctic and antarctic we have the midnight sun in summer and no sun over the horizon in winter. Surprisingly, we can use a Ptolemaic idea to explain this. In Ancient Greece, they imagined that the objects observed in the sky were placed on a series of concentric spheres around the Earth. While we no longer imagine celestial bodies pinned to spheres of quitessence, the idea of the celestial sphere is still useful for mapping the apparent paths of any astronomical body in the sky. From our perspective on the surface of our planet, the sun traces a arc path across the sky, like that in the photo above. On any day this path is of course due to the rotation of the Earth around its axis. Over the course of the year, because of the tilt of the axis, the position of the arc varies as the earth completes its rotation along its elliptical path around the sun. At the equator, the the path of the sun in the sky makes an untilted arc to the north or south of the celestial equator (the imaginary line cutting the imaginary sky sphere in half). As we move away from the equator, the relative path of the sun appears more and more tilted (directly proportional to latitude). This tilt means the paths of the sun at the extremes of the yearly orbit, the two solstices, are quite different lengths. Away from the equator, the apparent path of the sun is quite long (maximal, in fact) at the summer solstice and quite short at the winter solstice. The image below shows the extemes of the paths of the sun on the celestial sphere above a point at mid-latitudes. If you go to higher latitudes this tilt of the two extreme paths of the sun become more and more tilted until the winter path is entirely below the horizon.

There are other astronomical cycles which affect our Earth, but which are not easy for individuals to observe, because they are much longer than human lifespans. These are known as the Milankovitch cycles and include things like procession of the Earth's axis (which moves like the children's toy, a spinning top or gyroscope) over a cycle of roughly 26,000 years.

Different cultures have developped different calendars, often, if not exclusively, based on their astronomical observations. In ancient Mesoamerica, the Long Count calendar broke time into a variety of units, as we do (days, weeks, months, years, centuries, millenia, eons). They had K'in (one day), Winal (20 days), 1 Tun = 18 Winal (360 days, almost 1 year), 1 K'atun = 20 Tun (7200 days, almost 20 years), B'ak'tun = 20 K'atun (144,000 days or almost 394 years), Piktun = 20 B'ak'tun (2,880,000 days or roughly 7,885 years), Kalabtun = 20 Piktun (57,600,000 days or roughly 157,704 years), K'inchiltun = 20 Kalabtun (1,152,000,000 days or roughly 3,154,071 years), Alautun = 20 K'inchiltun (23,040,000,000 days or roughly 63,081,429 years). Today happens to be the end of a B'ak'tun, which while nifty, it is not the end of the Mayan calendar. In the Mayan notation this day would be which would have last occurred at the mythical creation day of this the fourth world, Monday, Aug 11, 3114 BCE (which is no more accurate, of course, than Bishop Usher's date, since of course, our planet is roughly 4.2 billion years old). The image at left shows the east side of stela C, Quirigua with mythical creation date in 13 (or 0) baktun, 0 katun, 0 tun, 0 uinal, 0 kin, 4 Ahau and 8 Cumku and corresponds to August 11, 3114 BCE in the Gregorian calendar (via wikipedia). Now previous worlds in the Mayan mythology only lasted 13 B'ak'tun, but there are inscriptions which refer to the end of the Piktun, which will not occur until 13 October 4772, so it's clear they assumed the world would be around a lot longer than this one solstice. So, if you would like to celebrate, celebrate the lengthening of days (at least here in the Northern Hemisphere), or go ahead and celebrate the end of the Mayan B'ak'tun as a notable date to a fascinating culture, or with tongue planted firmly in cheek, the bizarre variation on millennial pop culture myths of the end of days. Strange eschatological misconceptions seem like as good an excuse for a party as any. It'll be a while until we have the next prediction of an apocalypse.

(x-posted to minouette)

Saturday, December 8, 2012

Sound (Visual) Art

Source: via minouette on Pinterest

"Bowhead," a picture of a sound made by a Bowhead whale, 2003 by Mark Fischer (using wavelet analysis of recorded hydrophone sound data)

Artist Mark Fischer was interested in whalesong and found that in the literature you could find information on the range of frequencies employed, or fourier transforms of recorded sound (so you could see it plotted as a function of frequency, or moreorless which 'notes' were used, if whales happened to use discrete notes like most human music). He decided to use a method common in my field - marine geophysics. He employed wavelet analysis. (If you're interested, this is something seismologists typically use. They take time series data, which means they measure the amplitudes of vibrations, which is often equivalent to measuring the intensity of sound, periodically, so they get a series of measurements in time. They convolve the time series with a wavelet, a specific function. The result is a matrix of numbers which can be displayed as a 2D image if you simply map numbers onto colours.) It suffices to understand that there are a series of numbers (equivalent to the whalesong) to which he applies a mathematical procedure to produce an image. As he writes,
The procedure I have developed to pursue this exploration is, to me, a form of photography- with mathematics as the lens and a computer as a camera. What results is something I call 'the shape of the sound'.

More recently he's produced wavelet images of birdsong and insect noises and what he calls 'AguaSonic' videos of various species, so you can hear the animals too.

Source: via minouette on Pinterest

Pseudorca Pontinha by Mark Fischer, 2009 17.75" x 23.75" archival digital print on Crane's Museo Max paper

Sound as visual art can also be of sounds closer to the human experience (and not only those which require hydrophones to record). Epic Frequency makes prints of famous audio clips. This one is Martin Luther King, Jr. beginning, "I Have A Dream" On August 28, 1963.

Or, here is a way in which natural sounds combine with sculptural art. 'Hear Heres' is a set of four giant ear trumpet sculptures designed to highlight the sounds of nature, by London architecture firm Studio Weave.

Hear Heres

Hear Heres

Hear Heres


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