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Certification & Training

PDC Test - Darkness in Broad Daylight

You can earn 0.25 PDC by passing the exam following this article, which has been approved for publication by NCRA's Council of the Academy of Professional Reporters.

The questions are based on the material in the article but some may require additional research. Send your answer sheet to NCRA's Continuing Education Office, 8224 Old Courthouse Road, Vienna, VA 22182, and enclose a check for $40 (member) or $50 (non-member) to cover the processing fee. 


Darkness in Broad Daylight

by Susan Naylor

Imagine yourself as one of man's early ancestors. You become accustomed to seeing the sun in the sky for a period of time, seeing it disappear for a period of time, and then predictably reappearing. One day, however, something very unexpected happens. While the sun is in the sky, daylight suddenly begins fading. When you look up, you catch a glimpse of something dark moving across the face of the sun. Soon it has almost completely covered the sun. An odd quiet falls as darkness descends over the land. The air cools. The brighter stars and planets appear. Animals, disoriented by the sudden darkness, yelp and howl. Birds become silent and still. Others in your group shudder in fear and wave their arms in an attempt to drive away whatever is trying to take the sun from the sky.

The word "eclipse" comes from the Greek word "ekleipsis," meaning abandonment. Literally, an eclipse was seen as the sun abandoning the earth. Early man regarded eclipses as bearers of ill omen. In many ways, it makes sense that eclipses would be seen as bad omens for the early cultures. The sun was seen as a life-giver, something that was there every day, so something that blotted out the sun was a bad event.

Solar eclipses often appear in mythology and literature of different cultures and ages, very often as symbols of destruction, fear, and the overthrow of the natural order of things. God told the Old Testament prophet Amos, "I will make the sun go down at noon and darken the earth in broad daylight." The ancient Chinese believed that solar eclipses were caused by a dragon trying to swallow the sun. Predicting eclipses and ensuring that the nation was prepared to ward off the dragon was one of the jobs of the court astronomers. To this day, the Chinese word for a solar eclipse is "resh," or "sun-eat." As early as six centuries before the birth of Christ, the "Book of Songs," one of the five Confucian Classics, termed solar eclipses "ugly" and "abnormal." During Caesar's reign in Rome, there was such certainty that an eclipse was caused by gods venting their displeasure against man that it was considered a crime to suggest that there might be a natural cause for the event. For most of human history, people did not understand what a solar eclipse was.

Through centuries of studying the relationship between the earth, sun, and moon, we have come to understand that eclipses are a natural phenomenon, brought on by very specific conditions. Eclipses can only occur during the time of a new moon. Why doesn't the moon get between the sun and earth every month at this period and produce an eclipse? The orbit of the earth around the sun and the moon's orbit around the earth are not perfect circles, but rather slightly oval-shaped ellipses. Also, these orbits are not parallel to each other in the same plane. As our planet orbits the sun, taking one year to complete its journey, it appears to us on earth that the sun moves against the background of stars, making one circuit of the sky in one year. If the sun could draw a line showing this path, we would see a great circle called the "ecliptic." If the moon also drew a line as it orbited the earth, we would see that the two lines would be close to one another, but the moon's path is tilted about 5 degrees to the sun's path. This is the reason the moon doesn't eclipse the sun every month. Most often, the moon will pass above or belowthe sun.

An eclipse can occur only when both the sun and moon arrive near one of the crossing points called "nodes." There are two nodes on opposite sides of the sky, one where the moon crosses from south to north, and one where the moon passes from north to south. Since there are two crossing points in the sky, eclipses happen during two eclipse seasons, separated by about six months. The sun does not have to be right on the node when the moon arrives at this point, only close enough for the moon to block a portion of the sun. This creates a window of about 18.75 days before and after the sun gets to the nodes. During this 37.5-day period, the moon can cause an eclipse.

The three types of eclipses that can occur depend on several things. Total solar eclipses happen when the "umbra," the totally dark portion of the moon's shadow, touches a region on the surface of the earth. Partial solar eclipses occur when the "penumbra," or semidark portion of the moon's shadow, passes over a region on the earth's surface. If the eclipse happens when the sun is further away from one of the nodes, it is more likely that the eclipse will be a partial one. In this type of eclipse, the umbra passes above the north pole or below the south pole, never touching the earth. All we ever see is part of the sun covered. Annular (from the Latin "annulus," or ring) eclipses occur when a region on the earth's surface is in line with the umbra, but the umbral shadow is too short to reach the earth. You will see a ring of the sun shining around the edges of the moon.

Another factor exists, though. Remember that the orbits of the earth and moon are not perfect circles, but rather ellipses. The earth is sometimes closer to the sun and sometimes further. The same is true for the moon. Sometimes it is closer to the earth, and sometimes it's further. Both the sun and the moon change their distances quite significantly. The moon changes its distance to earth by about 14 percent, and we vary our distance to the sun by about 3 percent. Because of this, the sun and moon look bigger sometimes and smaller at other times. If we're far from the sun so that it looks smaller and close to the moon so that it looks bigger, the moon will be able to cover the entire face of the sun as seen from the earth, and we'll see a total eclipse. If the opposite is true and we're closer to the sun and farther from the moon, the moon will apear too small to cover the face of the sun. This will produce an annular eclipse.

The star of the show, the sun, is a thermonuclear furnace with a surface temperature of about 6,000 degrees Centigrade. The word "surface" is a bit misleading, as the sun is not a solid ball, but rather a gaseous body. If you heat up a gas enough, it becomes ionized (loses outer electrons) and the gas becomes opaque. The opaque and very bright surface of the sun is called the "photosphere." Because the gases of the photosphere are moderately dense, they give off an incandescent white light like the filament of a lamp.

Above the photosphere, the gases are cooler, more rarefied, and give off a spectrum of light that is representative of the chemical elements that compose it. This thin layer, the upper atmosphere of the sun, is called the "chromosphere" because of its colorful nature. Normally you can't see the chromosphere, but the eclipse gives us just the right conditions to observe this beautiful phenomenon.

There are always eruptions on the sun which throw huge amounts of glowing gas, often much larger than the earth, high above the sun's surface. They may hang suspended for many days, often reaching high into the sun's corona. The huge jets and loops of gas around the edge of the sun follow magnetic fields usually emanating from the sunspots. These "prominences" are visible along the very thin edge of the sun during a total eclipse.

The sun's incredibly hot outer atmosphere is called the "corona." It is heated to as much as 2 million degrees Fahrenheit by forces from the sun's photosphere. It is a thin haze of electrically charged atoms, mostly hydrogen and helium. It is only visible during totality.

If you are lucky enough to be in the path of totality, you will witness a spectacle. As the moon comes between us and the sun, the first bite is taken out of the edge of the sun's disk. This phase of the eclipse continues for about the next 90 minutes. The lighting around you becomes very strange, becoming gray instead of the oranges and reds we see at sunset.

A few minutes before totality, some unusual effects can be seen. You may think that the light is playing tricks with your eyes if you notice bands of shadows moving across the ground. These shadow bands form from refraction, or bending of light, in the earth's atmosphere, similar to what you might see on the bottom of a pool of water. A vast and dark shadow can be seen to the west, approaching at supersonic speed. It will appear as a storm forming in the west as the sky darkens. An eerie quiet falls as darkness descends. It is night, surrounded by day on the horizon. If there are animals around, they become quiet and prepare to sleep. At the same time, nocturnal animals get ready to come out.

In the final instant before totality, the photosphere shining through valleys in the moon's surface gives the impression of beads on the periphery of the moon, a phenomenon called "Bailey's beads," named after the amateur astronomer who called attention to them. The last bit of the sun's blazing photosphere disappears, and you will see something called the "diamond ring effect," the beautiful corona forming a ring around the moon with a brilliant white jewel of light, the last Bailey's bead. After the diamond ring disappears, you have only a couple of seconds to notice the reddish-colored chromosphere before it is eclipsed. Within moments, all direct sunlight vanishes. When the sun is completely hidden, which can last up to 7-1/2 minutes, you will see a pale, shimmering halo of light. This is the sun's corona. You may also see the prominences. They are the beautiful crimson color of glowing hydrogen gas and the violet of ionized calcium.

Things that you cannot see will also be happening. Many shortwave radio stations that are undetectable during daylight are now easy to pick up. The reason has to do with the sun's effect on earth's atmosphere. Ordinarily during daylight hours, atoms and molecules in lower regions of the ionosphere are ionized by the sun's ultraviolet radiation and act as resistors to radio waves with shortwave frequencies. During nighttime -- or during the brief period of darkness when a solar eclipse occurs -- the resistance in those layers drops. As a result, shortwave frequencies are able to reach the ionosphere's upper layer and bounce back to earth, becoming exceptional transmitting frequencies.

The total phase is the only time a solar eclipse is safe to view with the naked eye. Partial, annular, and partial phases of a total eclipse are never safe to watch without eye protection. The safest and most inexpensive way to view an eclipse at these stages is by projection, where a pinhole is used to cast an image of the sun on a piece of light-colored paper or other material placed a few inches beyond the opening. There are also special filters designed for this purpose. These filters usually have a thin layer of aluminum, chromium, or silver deposited on their surfaces that attenuates ultraviolet, visible, and infrared energy.

The next total eclipse visible from North America will occur in 2017. Other than the fact that they are rare events, it is the spectacular view of a total solar eclipse that makes people want to see them. There are no words or pictures to adequately describe what one sees without making it sound like a religious experience or something beyond imagination. It is a stunning reminder of man's small place in the universe.


Acknowledgements:

"Eclipse Predictions" by Fred Espenak
Fred Espenak's Home Page
NASA/GSFC Sun-Earth Education Forum
"Layers of the Earth's Atmosphere" from "Windows to the Universe"
Exploratorium
Las Vegas Review-Journal, 6-30-91

Information Resources:

http://www.mreclipse.com
http://www.sunearth.gsfc.nasa.gov/eclipse/eclipse.html
http://www.windows.ucar.edu
http://fusedweb.pppl.gov
http://csep10.phys.utk.edu (Astronomy 161, The Solar System)
http://www.exploratorium.edu

 

About the Author: Susan Naylor, RMR, is from Henderson, Nev.

 

 


 

Test for "Darkness in Broad Daylight"

1. "Ekleipsis" is the ______ word for abandonment.r

(a) Latin
(b) Greek
(c) Chinese
(d) Hebrew

2. Eclipses can only occur during:

(a) a full moon
(b) a new moon
(c) a crescent moon
(d) a waxing moon

3. Orbits of the moon around earth and earth around the sun are:

(a) elliptical
(b) lie parallel to each other
(c) tilt 5 degrees with respect to each other
(d) both a and c

4. Eclipses do not occur every month because:

(a) the sun is too high in the sky
(b) the moon and sun are too far from the nodes
(c) the moon passes above or below the sun
(d) both b and c

5. There are ___ nodes on opposite sides of the sky.

(a) 7
(b) 5
(c) 10
(d) 2

6. The sun must be exactly at one of the nodes for an eclipse to occur.

(a) True
(b) False

7. The portion of the moon's shadow that completely blocks the sun is called:

(a) perihelion
(b) umbra
(c) node
(d) penumbra

8. An annular eclipse:

(a) can be compared to placing a dime in front of a penny
(b) happens when the umbra does not reach earth
(c) happens when the earth is closer to the sun and farther from the moon
(d) all of the above

9. The penumbra:

(a) is the semidark portion of the moon's shadow
(b) is the totally dark portion of the moon's shadow
(c) forms a halo around the moon
(d) has no influence on what type of eclipse occurs

10. The moon changes its distance to earth by:

(a) 3 percent
(b) 6 percent
(c) 14 percent
(d) 25 percent

11. The sun's photosphere is:

(a) about 6,000 degrees Fahrenheit
(b) about 10,000 degrees Fahrenheit
(c) about 10,000 degrees Centigrade
(d) about 2 million degrees Fahrenheit

12. The chromosphere:

(a) is only visible during a total eclipse
(b) gives off light representative of its chemical composition
(c) is the outermost atmosphere of the sun
(d) both a and b

13. Sunspot activity takes place:

(a) in the photosphere
(b) in the corona
(c) in the chromosphere
(d) in the ionosphere

14. Prominences:

(a) do not occur frequently
(b) are about the size of the earth
(c) follow magnetic fields
(d) are visible at any time

15. The sun's corona:

(a) is what you will see first during an eclipse
(b) is the coolest portion of the sun's atmosphere
(c) disrupts radio broadcasts
(d) is composed of mostly hydrogen and helium

16. Refraction refers to:

(a) the act of reducing or compressing
(b) light shining through a surface
(c) the bending of light
(d) the return of light from a surface

17. Bailey's beads are the result of:

(a) the sun's photosphere shining through valleys in the moon's surface
(b) eruptions on the sun's surface
(c) light being reflected by the moon
(d) prominences visible above the moon's surface

18. Ionization refers to:

(a) loss of a proton
(b) loss of an electron
(c) loss of a neutron
(d) loss of an atom

19. A safe way to view an eclipse is:

(a) during the time the sun is completely blocked by the moon
(b) through a special filter
(c) by the pinhole method
(d) all of the above

20. The longest total eclipse can last nearly:

(a) 5 minutes
(b) 3 minutes
(c) 10 minutes
(d) 7 1/2 minutes

21. The chemical symbol for hydrogen is:

(a) Hg
(b) Ho
(c) H
(d) He

22. As early as 6 A.D., eclipses were described as ugly and abnormal in one of the five Confucian Classics.

(a) True
(b) False

23. The moon takes ____ days to go from new moon to new moon.

(a) 18.75
(b) 29.5
(c) 37.5
(d) 31

24. The diamond ring effect is produced by:

(a) the corona and the last Bailey's bead
(b) the photosphere and the last Bailey's bead
(c) annular eclipses
(d) Bailey's beads only

25. The term for earth or another celestial body being closer to the sun is:

(a) Perihelion
(b) Aphelion
(c) Saros
(d) Heliocentric

 

Answer Sheet for Darkness in Broad Daylight

Circle the correct answer


Name ______________________________________________

Address ____________________________________________

Membership ID Number _______________________________


1.   a    b    c    d

2.   a    b    c    d

3.   a    b    c    d

4.   a    b    c    d

5.   a    b    c    d

6.   True    False

7.   a    b    c    d

8.   a    b    c    d

9.   a    b    c    d

10.   a    b    c    d

11.   a    b    c    d

12.   a    b    c    d

13.   a    b    c    d

14.   a    b    c    d

15.   a    b    c    d

16.   a    b    c    d

17.   a    b    c    d

18.   a    b    c    d

19.   a    b    c    d

20.   a    b    c    d

21.   a    b    c    d

22.   True    False

23.   a    b    c    d

24.   a    b    c    d

25.   a    b    c    d