20 March 2011


2011 VERNAL EQUINOX. Today at 2321 hours UTC (once known as Greenwich Mean Time) marks the time of the Spring equinox. We experience seasons not because the Earth orbits appreciably nearer or farther from the sun during each year's circuit, but rather because the Earth's rotational axis is tilted 23.4 degrees from vertical, with respect to the plane of Earth's orbit (also known as the plane of the ecliptic -- see images above and below, click to enlarge). When the north pole is tilted away from the sun, the northern hemisphere experiences winter, when days are shorter and nights are longer. When the north pole is tilted toward the sun, summer visits the northern hemisphere, with longer days and shorter nights. But when the tilt is neither away from or toward the sun, each hemisphere experiences an equal period of daylight and darkness. As you might intuit, this happens twice a year, the Vernal and Autumnal equinoxes.

Among Earth's cultures, the equinoxes and the winter and summer solstices have been celebrated for millenia. The respective equinoxes are often marked by planting and harvest festivals. Interestingly, these observances have been co-opted by religions, notably Christianity, with their celestial, seasonal and pagan significance transferred to ecclesiastical events.

To discover the exact time when the equinox occurs in your time zone, here is a handy time zone chart, with explanations beneath. Locate your time zone, then simply add or subtract the appropriate number of time zones from UTC (depending on whether you are east or west of the prime meridian), and there you have it. As an examply, Mountain Daylight Time is six hours earlier than UTC, so this year's equinox occurs at 1721 hours (5:21 PM) where I live.

RADIATION CHART. This is the real deal -- and it's a stunner. Below you will find a chart which shows the relative doses of radiation one absorbs when exposed to an array of activities and circumstances, ranging from living near Chernobyl to eating a banana, from receiving an X-ray to spending time at higher elevations (with less atmospheric protection from the sun). Given the current nuclear crisis in Japan -- and here is what you need to know at present -- this radiation dose chart puts things in perspective. You will definitely need to click on the image (once for preliminary enlargement, then again to magnify a portion of the chart) for best legibility.

No comments:

Post a Comment