On Monday, August 21 we will be treated to a real rarity – a total solar eclipse.  Totality may be observed in the contiguous states of the US in a narrow band approximately 70 miles wide stretching from Oregon (beginning at 9:06 am PDT as a partial) through Idaho, Wyoming, Nebraska, Missouri, Illinois, Kansas, Kentucky, Tennessee, North Carolina, Georgia and South Carolina (ending as a partial at 4:06 EDT).

Each of these states is preparing for a substantial influx of “umbraphiles,” aka “eclipse chasers,” most of  whom are attracted by the adventure and rarity of the event, rather than the science of it.  In an attempt to accommodate these umbraphiles as well as their own citizens, each state has planned central viewing areas and celebrations, such as special NASA-sponsored presentations, festivals, entertainment and educational seminars, mostly to be held in outdoor stadiums, fair grounds and parks.   One special event will be Royal Caribbean Cruise Line’s special presentation of Bonnie Tyler performing her famous 1983 hit song, “Total Eclipse of the Heart,” on board one of their cruise ships as it crosses the path of totality.  In addition, various media outlets will be covering the eclipse.

The length of time for totality will vary, with the longest period being two minutes and 41.6 seconds.  Partiality may be viewed in the rest of the US as well as Canada and parts of Mexico, Central and South America, northwestern Europe and Russia.

There are four types of eclipses:

  1. Total – when the Moon completely obscures the Sun.  This only occurs briefly along a narrow track.
  2. Annular- The Sun and the Moon appear to be exactly in line with the Earth, but the Moon appears to be smaller.  In this case, the Sun will appear as a bright ring, or “annulus,” around the dark disc of the Moon.
  3. Hybrid – Shifts between a total and an annular eclipse at different points.  These are relatively rare.
  4. Partial – The Sun and Moon are not exactly in line, and therefore, the Moon only partially obscures the Sun.

The previous total solar eclipse visible across the entire contiguous US was on June 8, 1918.  The next total eclipses visible in the US will be in April 2024 and August 2045.

Briefly, a solar eclipse occurs when the Moon passes between the Sun and the Earth obscuring (or “occulting”) part or all of the Sun. The technical term for this phenomenon is “zyzgy.”  The orbital planes of the Earth and the Moon do not match up perfectly.  The Moon’s is tilted at approximately five degrees in relation to the Earth’s.  If not, there would be a total solar eclipse every month.  In actuality, one occurs somewhere on earth about twice a year.  The reason why they seem to be so rare is that each total eclipse only occurs over a narrow band, so that one can be observed in any particular place only every 360-410 years on average.

Even though the Sun is approximately 400 times the diameter of the Moon, the Moon is approximately 400 times closer to Earth.  Thus, when viewed from Earth they appear to be the same size in the sky.  So, if the alignment of all three celestial bodies is just right, the Moon can and does obscure the entire sun, producing a total eclipse.  During totality it will get dark and only a corona around the sun will be visible.

We all have been amply warned that viewing the eclipse directly with the naked eye can cause severe retinal damage or even blindness.  It is imperative, therefore, to wear special glasses that are able to filter the sunlight safely.  Beware of using unsafe glasses or homemade devices.  Also, keep pets inside and away from windows and skylights.

Ancient people, who were very superstitious and ignorant of astronomy, feared eclipses.  To them, the sudden darkness could only mean they were incurring the wrath of the gods and, perhaps, they portended the end of the world.  There are many stories , or, perhaps, legends, around eclipses.  For example, supposedly, an ancient Chinese king beheaded two of his astronomers who had failed to predict one.  Also, in ancient Greece during a battle between the Medes and the Lydians both sides were so taken aback by an eclipse that they summarily put down their weapons and declared a truce.

CONCLUSION

Unless you are an astronomy aficionado you are probably not all that interested in all the technical jargon surrounding the science of eclipses.  Suffice to say that, for many people, eclipses constitute a seminal event in their lives.  Enjoy the experience.  It does not occur often.

But, above all else, be safe!