2007-09-19 / Families & Friends

Change of seasons doesn't always follow the calendar

Mother Nature seldom looks at a calendar when deciding that leaves should change color, when the first snows will fly, or when it is time for spring to return. Give a month or two, seasons change and usually reach at least a general proximity of what we expect as normal for that particular season. For example, when you think of a fall day, the image that comes to mind is woods blazing with colors with the days cool, nights crisp, and the skies a brilliant blue. And that image is usually associated with late September or early October. But having a general time frame is not agreeable to man. We like things to be more predictable, with a way to measure or to give a point of reference to events that we cannot really see. So a very long time ago, man developed a calendar to keep track of time and important events over time.

Early man realized that days were longer in the summer, shorter in the winter, and spring and fall held about equal amounts of day and night. They noticed that every day produced a change in the sun's elevation in the sky, except for about a week when the sun was at its highest elevation (summer) and at its lowest (winter). During the time of the shortest day and the longest night of the year (winter), and the longest day and the shortest night of the year (summer), the sun appears to hold about the same noontime elevation for several days before and after. Hence the origin of the word "solstice", which comes from Latin solstitium, from sol, meaning "sun" and -stitium, "a stoppage." The spring and autumn events were named "equinoxes" meaning "equal", referring to equal amounts of day and night, and "solstices" to designate the longest and the shortest days.

When it is winter for us here in the northern hemisphere, it is summer in the southern hemisphere. The reason for the opposite seasons at opposite times of the year between the two hemispheres rests with the earth's rotation about the sun. During this journey, the earth also spins on its axis, which is tilted some 23.5 degrees towards the plane of its rotation. In plain language, this means that when the North Pole is pointed the farthest away from the sun, the sunlight striking the northern hemisphere is at an angle, the northern hemisphere receives less direct sunlight (creating winter) while the southern hemisphere receives more direct sunlight (creating summer) as the suns rays are nearly perpendicular. As the Earth continues its orbit, the hemispheric pole that is angled closest to the sun changes and the seasons for the two hemispheres are reversed. In between these two extremes, are the spring and autumnal equinoxes.

Those are the physical points of reference that man learned to measure and they can be predicted years into the future. But actual weather patterns usually lag behind the actual point on the calendar. For example, although the first day of summer on the calendar falls in late June, the real heat of the summer does not appear until late July and August and often lingers into September. The same is true of winter, which officially begins just before Christmas. January and February historically hold the brutal cold months of winter, but it is often March that can produce the most brutal storms of the winter season.

The reason for this time lag is that it takes time for the earth to warm up, and it takes time to cool down. After a scorching hot summer, even though there is much less daylight as the official winter date on the calendar approaches, the earth retains this summer heat stored in the land and in the oceans. Once the winter solstice is passed, the maximum cooling on the earth will take place as the last of the stored summer warmth is lost. The reverse holds true for warming the planet as summer approaches.

On the calendar, with the solstices to mark the first day of summer and winter, it is the equinoxes which mark the first days of spring and autumn. All these solar events usually occur near the 21st of the months with December for winter, June for summer, spring in March, and September for fall. The exact date varies; in some years, as early as the 20th to as late as the 23rd for the season change. This year, fall begins on Sept. 23, and winter officially arrives on Dec. 22.

In the early days before computer equipment, satellites, and other modern marvels, ships at sea required the exact time in order to navigate. The earth's exact position in its relation to the sun was vital. Initially, American scientists and seamen relied on foreign almanacs - particularly those of Great Britain - for astronomical and navigational data. However, as the United States had a series of significant conflicts with the British at this time in history, it was essential that we developed our own means of keeping time. In 1849, Congress established the Nautical Almanac Office to prepare and publish an official national almanac. Privately published almanacs, such as Benjamin Franklin's Poor Richard's Almanac, were generally not adequate for scientific use. The Nautical Almanac Office, part of the Navy, became the U.S. Naval Observatory, and the official timekeepers for the United States. If you need to know the correct time, these are the people to go to. They are also responsible for calculating the date and time for all astronomical phenomenon such as phases of the moon, eclipses, and marking the seasonal change. According to the U.S. Naval Observatory, fall will officially begin this year on Sept. 23 at 5:51 a.m. EDT. Winter will officially start this year at 1:08 a.m. EST, Dec. 22, when the northern hemisphere is at its greatest declination from the sun and with the sun's rays striking the earth at the greatest angle.

For more interesting information on the solstices, history of the calendar, history of keeping time in general and its importance to navigation, information on the phases of the moon, sun, and other astronomical phenomena, or if you would just like to know the exact time to the second, visit the web site of the U.S. Naval Observatory at http:// aa.usno.navy.mil.

For information as to what is in store weatherwise for east Kentucky, visit the NOAA National Weather Service office in Jackson at www.weather.gov/ jacksonky.

Return to top