Darkness, in the middle of the day. The Sun is blocked out, and night falls ... much too early.
The Moon orbits around the Earth every month, and twice a year it passes in front of the Sun. Twice a year its orbit aligns with the Earth's orbit about the Sun as the Moon becomes new, and it passes directly between the Earth and Sun, blocking the Sun's light and casting its shadow on the Earth.
A total solar eclipse is one of the most spectacular natural events. The few minutes of total darkness are preceded by an hour of gradually decreasing sunlight. Air temperature falls. Winds and weather may change quickly. Birds and other animals may become confused as night apparently comes early. During totality, the landscape is darkened; the sky goes black, and stars may become visible. The sun is hidden, but it's position in the sky remains marked by the crown of light from its outer atmosphere. After a just a few minutes though, a ray of sunshine returns, and gradually daytime revives. A total solar eclipse is an awesome experience.
Or so I told my astronomy students. Every semester I would recount this celestial ballet. I knew the facts and explanations well enough to make the awesome events interesting to those who had never seen one . . .
But the eclipse lecture always left me feeling a bit empty. The reason-- I was passing on book knowledge, an understanding of concepts that I had read about ... but had never experienced myself.
And so, after my second year of teaching astronomy, I resolved to correct this deficiency-- I would go and see a total solar eclipse.
Solar eclipses happen twice every year. (More precisely, they occur every six synodic months.) But most are only partial, not total. And even when the Moon blocks out 70 or 80 percent of the Sun, human eyes adjust to the decreased illumination; many people subjected to a partial solar eclipse may remain completely unaware of the celestial aligment above.
Total solar eclipses are not only less frequent, they are very localized. The shadow of the Moon (umbra) is a tapering cone, and as it falls on Earth's surface it is only a few hundred kilometers wide at most. As the Moon moves in its orbit, the shadow moves across the Earth, tracing out a path of totality-- Only within this region will sunlight be completely cut off and observers experience a total eclipse. The rapid motion of the shadow also means that totality only lasts a few minutes at most.
So, to view nature's greatest astronomical spectacle, one must be in the right place, at just the right time.
As a teacher of science, I continually stress to my students the Scientific Method-- observation of regularities or patterns in the world around us, a hypothesis or theory to explain the regularities, and then a prediction or experiment to test the validity of the hypothesis.
I also like to point out that astronomy may be considered the oldest form of science, because people have been using this method to understand and predict lunar and solar eclipses for longer than recorded history.
Basic predictions are easy-- lunar eclipses can only happen at full moon, solar eclipses at new moon. The synodic period of the Moon's phases is 29 1/2 days. But eclipses do not occur every month.
The Moon does not orbit Earth exactly in the same plane that Earth orbits the Sun. In actuality, the Moon's orbit is tilted about 5° from the ecliptic plane. Therefore, usually the Moon passes above or below the Sun, above or below Earth's shadow, in its monthly path around the sky. The plane of the Moon's orbit intersects the ecliptic plane along a straight line, called the line of nodes. The nodes are the two points on opposite sides of the Moon's orbit where it crosses through the ecliptic plane. For an eclipse to happen, the Moon must be passing through one of the nodes at the same time it is New or Full.
This happens twice a year, each. Thus, eclipses come in pairs, about 6 months apart.
But not simply 6 calendar months. There must be an integer number of synodic months between eclipses, since solar (or lunar) eclipses can only occur at New (or Full) Moon.
6 synodic months = 177 days between successive solar (or lunar) eclipses.
12 synodic months = 354 days, which means that from year to year, eclipses occur about 11 days earlier on the calendar.
And this regularity is occasionally altered as the line of nodes (which is actually rotating slowly a result of the 18.6 year precession of the Moon’s orbit) gets out of sync with the line toward the Sun, and causes a skip of an extra (7th) month between eclipses.
But there is still a predictable pattern to eclipses, just on a longer timescale, that’s all. Every 18 years 11 1/3 days the precessing line of nodes and the lunar phases are in sync, and eclipses repeat themselves. In three times this time period (54 years, 34 days), even the geographical location of the eclipse path is similar. This 54-year repeating pattern (called the saros) was realized by ancient astronomers, whose job it became to predict solar and lunar eclipses.
Modern astronomers have gotten VERY good at precisely predicting eclipses. I personally am not one of those doing the predicting of eclipses (my research has focused on exploration of the planets and their satellites through space missions), but I have personally 'tested' many of the predictions of other astronomers, and I trust them with a high level of confidence.
The predictions told me that there would be a total solar eclipse on the 29th day of March, 2006, with a path of totality tracing across the south Atlantic Ocrean, the Sahara Desert of Africa, the Eastern Mediterranean Sea, the Anatolian peninsula of Turkey, and into western Asia.
Turkey.
Istanbul.
The name and the image of this city resonated in my mind. Istanbul was once Constantinople-- capital of the Roman Empire for a thousand years!
And so my mind was set-- one way or another, I would be in Turkey on 29 March 2006. And I would put myself in the right place, at just the right time, to have the Moon pass exactly between me and the Sun, and cast its shadow on me.
For four minutes.
