UNDERSTANDING THE ECLIPSE Introduction ...

UNDERSTANDING THE ECLIPSE Introduction Eclipses are defined by early Greeks as shadow effects. (Tarbuck and Lutgcns, 1976). Astronomers consider eclipses as an outcome of the natural interaction of the major components of the "earth system" viz the sun, the earth and the moon. Some traditional adherents to the unknown consider eclipses as visitations from gods in reaction to human inconsistent behaviors. Consequent upon these definitions, eclipse events have led to mixed effects of fears, suspicion, superstition, inquiries, surprises, enjoyment, economic benefits and losses and in extreme cases they constitute health hazards to humans. Thus we pose these questions for explanations; 1. Are eclipses natural situations or threats from gods? 2. How do eclipses come about? 3. What lessons do we learn from eclipses with respect to their realities or otherwise, advantages and problems? 4. How do we react to eclipse events? The objectives of this paper are:  To explain the concept and phenomena of eclipses by identifying their causes, features, expectations and fears.  To explain how eclipse situations influence human behaviors, health conditions, environmental/meteorological conditions.  To attempt chronological explanations and projections of eclipses over some years.  A successful explanation in these directions will not only dismiss the fears, suspicions and superstitions about eclipses but also increase our knowledge of eclipses, interests in space explorations and encourage safe relations with the phenomena. Methodology To achieve the above objectives, this paper will:  Review the relevant characteristics of the sun, the earth and the moon as they relate to eclipse situations.  Examine the interactions of the sun, the earth and the moon that leads to eclipses.  Discuss the types of eclipses, their frequencies and projections to some years ahead.  Explain how eclipses are observed, eye safety in eclipse observation and the local weather conditions that affect effective eclipse observation.  It also explains the factors that influence eclipse observation.  Identify the importance of eclipse to man and make a conclusion. The Solar System: The solar system consists of the sun and nine planets suspended by solar gravity in space at varying distances from the sun. These planets revolve round the stationary sun along their respective elliptical orbits. The planets also have their respective satellites such as the moons, asteroids, comets, and meteoroids also revolving around their respective plants or their mother bodies (Table 1).

Table 1: The Features of the Planets in the Solar System

Planet

Velocity of

Distance from Sun in millions

Period of Rotation

Period of revolution

Mercury

58Km

I

108Km

59d 243d

88d 225d

revolution per second 47.9Km 35.0Km

12112

No of known Satellites 0 0

150Km

23h 56mAds

365.25d

29.8Km

12742

1

228Km

24h 47m 23 s

687d

24.1Km

6,800

2

778Km

9h 50m

12yr

13.1Km

143.000

13

Saturn

l,427Km

10h 25m

29.5yr

9.6Km

121000

10

Uranus

2869Km

10h 45m

84yr

6.8Km

47,000

5

Neptune

4498Km

Approx. 16h

165yr

5AKm

45000

2

Pluto

5900Km

6A d

248yr

4.7Km

1 = total eclipse. 3. Duration is the time during which eclipse is effective in any particular place i.e. from the entry of the moon to the departure across the sun. 4. Region is the places where eclipse is visible. NASA has identified also that in America, the last total solar eclipse visible from the United States was on 26th February 1979, from Hawaii and Mexico 1117/91 and that the next two total solar eclipses visible from the United States will occur on 211812017 and 8/412024. In Nigeria, the last total eclipse visible in Central Eastern Nigeria was on 20/5/47 and in Maiduguri Nigeria - in 2001. It is not obvious when the next total eclipse will be visible in Nigeria after the 29th of March 2006. Our inquiries into space, and the use of the internet to discover existing knowledge are yet limited.

The March 29, 2006 Total Solar Eclipse On March 29, 2006, the moon was in a straight line between the sun and parts of Brazil, Ghana, Togo, Benin Republic, Nigeria, Chad, Libya, Egypt, Turkey, Black Sea, Georgia, Russia and Kazakhstan, to the Northern tip of Mongolia. The eclipse situation was from Eastern Brazil at about 7.38hours and into West Africa across the Atlantic at 9.14hrs. The eclipse left Africa into Eurasia at 1O.04hrs where it again lasted for another Ihr 9minutes from the Mediterranean Sea to the Northern Mongolian boundary with Russia at 11.50hrs. In all, the eclipse took 4hrs 12mins to travel diagonally approximately a distance of 16700Km covering between 380W and 1000E and across 580 of Latitude (from 80S to 500N). (Fig. 4.)

THE WORLD

FIG. 4: Total Solar Eclipse Track across the globe on 29/3/06

The approximate are covered by the total solar eclipse is 3.1 million square kilometers representing 0.61% of the earth’s crust surface area of 510m.Km2. Because of the curved nature of the earth's surface, the eclipse situation never occurs round the earth at the same time. Owing to the high speed of earth's rotation, the duration of the eclipse at a particular point is at most 5minutes from the entry of the moon to its departure from the path of totality. In Turkey where the eclipse is most prominent, it lasted for 3m 43seconds at Konya and 3 minutes 31 seconds at Ordu. The 'path of totality (within the umbra) is approximately 185km wide. On each side of the umbra, the penumbra is approximately 270km broad. This means that along a straight-line distance of 270km from the edge of the umbra, partial eclipse occurs. The degree of partiality is directly related to the distance from the edge of the umbra. In Nigeria, the eclipse lasted from 9.17hrs GMT in the South West to 9.38hrs GMT in Katsina at the Nigeria - Niger boundary. This represents approximately 863Km and an area of 159,692Km2 amounting to 17.3% of Nigeria's land area and 5.15% of all area affected by the eclipse. During these 21 minutes, different people experienced the total solar eclipse at different times and magnitude. About eight states were affected by the total solar eclipse. The states are Ogun, Oyo, Kwara, Niger, Zamfara, Katsina, Kebbi and Kaduna. Other states were peripherally affected by partial solar eclipse. Some eastern states were very minimally affected. Specifically, the centre of the path of totality is defined by a line running through Igana, Shaki, New Busa, Kontagora, Gusau, Katsina then into Niger Republic. (Fig. 5)

Fig.5: Eclipse Track in Nigeria, 29/3/06

On the eastern side of the path of totality, partial eclipse reached as far east as a line defined by Benin City, Auchi and across the Niger through Dekina, Keffi, Jos, Azare onto Adebour in Niger. Along this line, the moon on the sun was a faint crescent while solar brightness outside the crescent was severe and highly injurious to the eyes. The day was just as bright as an early morning in November/December period when the rising sun is just illuminating from beyond the horizon but gloomy with apparent rain cloud. The passage of the moon across the edge of the sun was swift.

On the western edge of the total solar eclipse region, the whole of Nigeria i.e. the entire remaining parts of Sokoto and Kebbi States were in the penumbra or partial eclipse region. However, the departure and approach effect on the eclipse magnitude made the duration elastic. This was similar to a sun-set sun-rise situation. The features of a Total Solar Eclipse are normally just like the characteristics of a dark night when there is the new moon i.e. the moon is unable to shine over you. Animals behaved true to nature by trying to return to their usual nocturnal niche. Nocturnal animals like bats came out. Humans, having been alerted remained calm knowing that the situation would quickly come to pass without any adverse effect. Stars appear in the clouds as the solar illumination which mutes their bright penetration is obscured. There is likely some level of anxiety among scientists and other earth scholars in their bid to understand more what was learnt earlier and then add new knowledge by way of discoveries. Lunar Eclipse Lunar eclipse or eclipse of the moon occurs only at full moon when the earth is in a straight line between the sun and the moon and the shadow of the earth is thrown on the moon. The earth's

shadow is of two shades. The full dark shadow of the earth called the umbra and the extended darkness where only part of the moon is faintly blocked and the part seen appears as a crescent/new moon. (Fig. 6).

Fig 6: The Geometry of Lunar Eclipse

As the moon is much smaller than the earth, and much nearer the earth than the sun, the moon does not cover the entire breath of the umbra. Consequently, the duration of the total lunar eclipse is long enough for observation than that of the total solar eclipse. Astronomers recognize three forms of lunar eclipse with specific features: (a) Penumbra Lunar Eclipse: This is when the moon passes across the earth's penumbral region in a

subtle manner. (b) The Partial Lunar Eclipse: Occurs

where a portion of the moon passes through the umbral shadow and is readily and easily seen.

(c)

(c) Total Lunar Eclipse: Occurs when the entire moon is within the umbra. It shows some vibrant range of colours that are available in the moon. The earth blocks solar light from reaching the moon as it passes across. Total lunar eclipse does not occur every month because the 50 inclination of the moon's orbit on the earth's orbit often throws the shadow of the earth outside the moon. However, the filtering and the refracting effect of the earth's

atmosphere faintly illuminates the moon so that it is not completely dark except when dust haze or volcanic ash is too dense to allow the penetration of refracted light. All total eclipses start with a penumbral as the earth enters the straight line, then a total, followed by another penumbral as the earth leaves the straight line from the other side. Lunar Eclipse Frequencies In the 5000 years from 2000BC projected to 3000AD, there are a total of 7718 lunar eclipses on the average of 1.42 eclipses per annum. However, lunar eclipse occurrences vary between 0 and three yearly excluding the penumbrals. Partial eclipses are more numerous at the rate of 7:6 than total eclipses. Table 4 below lists all the lunar eclipses in 10 years from 2000 projected to 2010.

Date

Eclipse Type

2000 Jan 21 2000 Jul 16 2001 Jan 09 2001 Jul 05 2001 Dec 30 2002 May 26 2002 Jun 24

Total Total Total Partial Penumbral Penumbral Penumbral

Umbral Magnitude 1.330 1.773 l.195 0.499 -0.110 -0.283 -0.788

2002 Nov 20 2003 May 16 2003 Nov 09 2004 May 04 2004 Oct 28 2005 Apr 24 2005 Oct 17 . 2006 Mar14 2005 Sep 07 2007 Mar 03

Penumbral Total Total Total Total Penumbral Partial Penumbral Partial Total

-0.222 1.134 1.022 l.309 l.313 -0.139 0.068 -0.055 0.189 1.238

2007 AU,g 28 Total l.481 2008 Feb 21 Total l.111 2008 Aug 16 Partial 0.813 2009 Feb 09 Penumbral -0.083 2009 Jul 07 Penumbral -0.909 2009 Aug 06 Penumbral -0.661 2009 Dec 31 Partial 0.082 2010 Jun 26 Partial 0.542 2010 Dec 21 Total l.262 Source: Fred Espenak (2000) vlwI11.MrEchpse.conz

Total Duration 78m 108m 01h02m

-

-

00h53m 00h24m 01h16m 01h21m -

01h14m

01h31m 00h51m -

-

0lh13m

Geographic Region of Eclipse Visibility Pacific, America, Europe, Africa Asia, Pacific, W .America E America, Europe, Africa, Asia E Africa, Asia, Aus., Pacific E Asia, Aus, Pacific, America E Asia, Aus, Pacific, W America S America, Europe, Africa, c Asia, Aus. America, Europe, Africa, e Asia c Pacific, America, Europe, Africa America, Europe, Africa, c Asia S. America, Europe, Africa, Asia, Aus. America, Europe, Africa, c Asia e Asia, Aus, Pacific, North America Asia, Aus., Pacific, North America America, Europe, Africa, Asia Europe, Africa, Asia, Aus America, Europe, Africa, Asia

e Asia, Aus., Pacific, America c Pacific, America, Europe, Africa S. America, Europe, Africa, Asia, Aus. e Europe, Asia, Aus. Pacific, W N.A Aus., Pacific, America America, Europe, Africa, W Asia Europe, Africa, Asia, Aus. e Asia, Aus., Pacific, W America e Asia, Aus., Pacific, America, Europe

Observing the Eclipse It is an interesting, historic and scientific learning experience to observe an eclipse as it may occur once in a one's lifetime. Observing the lunar eclipse poses no problems. It is possible to look at the moon and the stars with the normal eyes as the moon interacts with the sun and the earth. It is the solar eclipse that poses the danger of radiation injuries on the eye especially on the retina. The chemical emission from the corona and the chromosphere, are capable of damaging the eye rod by mutation. Solar partial, and annular eclipses and the waxing and waning phases of total eclipses are dangerous. If therefore the beauty of the eclipse is to be observed, and the science of the sun, the earth and the moon as well as their relationships are to be furthered, these bodies must be watched during the eclipses especially the solar eclipse. To do this, it is important to use properly filtered sun-glasses. This will enable safe and detailed study of the eclipse to be done physically. As before, NASA in America and other agencies on the space inquiry in Europe and China keep records of the proceedings and often transmit the progress at the internet. Local broadcasts in affected areas cover the interaction and keep people informed. Film makers and camera photographers take pictures of the situations. For all these viewing tools, it is expected that their lens be equipped with filters to avoid injuries to the eyes. Eye Safety in Eclipse Observation Apart from the radiation effect on the eyes, eclipse has no known adverse effects. It is advisable therefore to use the recommended glasses to observe the eclipse. Chou, (2005) recommended filtered glass with a thin layer of chromium alloy or aluminium deposits on the surface to attenuate visible and near-infrared radiation of less than 5% density or 0.003% density of visible light - about 780-1400nm or 380-780nm respectively (density 2.3) or (density 4.5) respectively too. One of the recommended available filters is shade number 14, the welder's glass commonly obtained from welders supply shops. In the alternative, an aluminized mylar manufactured lens specifically for viewing solar eclipses is recommended. This alternative is inexpensive and unlike the welder's glass, it does not easily break and can be cut to size to fit any viewing instrument including cameras not equipped with such filter during their manufacture. Many observers use a double layer of unused black and white film negative treated to maximum density and exposed to light. The metallic silver in the film emulsion provides the protective film. However film negatives with images on them are unsafe as openings exist through which radiation can penetrate to burn the retina. It is advised that people whose natural lens of the eye(s) have been tampered with as in the case of cataract patients, do not observe the solar eclipse even with the appropriate equipment (Priore, 1991).

As the total solar eclipse comes possibly once in one's life time, every opportunity should be explored to expose students properly to the experience. School masters and class teachers should provide or help pupils provide adequate viewing equipment for observing the eclipse well ahead of time and ensure that these are used properly during the time. Students who lost the chance of observing the eclipse as against others who did so without injuries will feel denied and will in future receive other health instructions from their teachers with a grain of salt (Rasecholl, 1997). To avoid this, it is advised that

students under supervision should avail themselves of dark green beer or malt bottle which should be recovered and disposed safely immediately after the exercise. Such bottles should be repainted with aluminum emulsion or oil paint to increase the safety chances. The Local Weather and Eclipse Observation This discusses how the meteorological phenomena in the eclipse area affects effective, detailed and accurate eclipse observation. An important variable in the effective observation of eclipses is the local weather condition at the time of umbra magnitude - the time the eclipse is at the best position for meaningful observation. This variable can be properly illustrated with the March 29th, 2006 solar eclipse in relation to the march of the thermal equator and the attendant meteorological conditions as they affect the eclipse area. Conceptually, visibility condition at the time of eclipse event determines how much of the eclipse features can be observed. Normal visibility is a function of the atmospheric conditions - cloud cover, haze, mist, fog and precipitation conditions that will ordinarily obscure sight and so prevent people from seeing the eclipse at all or clearly. The possibility of these weather conditions obtaining is again determined by the season, aspect, relief, and relative location - in relation to water and land masses. Using the 29th March 2006 eclipse as an illustration, a number of meteorological factors militate against the observation of the eclipse. These factors help to create congestion of solar eclipse tourists in selected towns as against the other towns in the hope that such towns would exhibit clearer atmosphere than others. It is noted that the 29 March 2006 eclipse event spans across 58 parallels from Lat. 80S to Lat. 50oN. This covers three atmospheric pressure zones - the Equatorial Lows, the Saharan Tropical Highs and the Mid Latitude Low Pressure region as they obtain ordinarily during the spring equinox. Following this pressure distribution, the resultant weather characteristics along the line of the eclipse include: a) An onshore SE Wind influenced by the warm Brazilian current, from the S. Atlantic Ocean brings onshore some moist air onto the low pressure region of S E Brazil. As a result, cloudy conditions, convectional precipitation and mist prevail in the area. These lead to low visibility. b) The same situation obtains in W. Africa sequel to the onshore trade wind on to the West African coast. The result also is cloudy weather, coastal fog and showers. The Inter Tropical Convergence Zone (ITCZ) centred on the Equatorial Low Pressure Belt mainly in the Southern Landmass of West Africa encloses these two areas. Here convectional rains, subsequent cloudy mornings and sea breeze are common and militate against proper visibility. c) In the northern part of Nigeria, beyond the Northern limit of the ITCZ, dry NE Trade wind blows from the Tropical High Pressure Region of the Sahara Desert. Since the wind is dry, the air is thus dry and the atmosphere is clear but for some occasional dust haze. Long duration of sunshine is common. In this region and in the Sahara itself such as in Libya and Chad, the sky is often clear. The towns of Katsina (Nigeria) and Zinder (Niger) are better centres of eclipse observation than at Keta (Ghana), Lome (Togo) Sokete (Benin) or Ogbomosho (W. Nigeria) d) During this season, Low Pressure conditions, and converging and rising air current prevails around the Eastern Mediterranean region giving rise to cloudy conditions from frontal winds

arising from air drafts from the mountains and the continental interior. Hot, dry and dusty weather prevails in areas removed from the oasis where haze is reduced. e) Turkey, Black sea, Georgia, and Southern Russia are climatically influenced by the eastward migrating and alternating Low pressure and High Pressure Systems. Besides, the region is rugged leading to forced air ascent and condensation leading to cloudy or foggy conditions with occasional thunderstorms. The low angle sun makes the cloud denser and observations more uncertain. f) Further north in the Russian Mountains- the Caucasus- and western Kazakhstan, the emerging polar Highs draft cold air into this Mid-latitude low pressure region. This tends to deny the air of moisture and deters eclipse observers from making use of the stations for viewing the eclipse. It is expected that meteorological observations and data keeping will be intensified and made more frequent as the eclipse day approaches. The nearest observation to the eclipse hour is taken to be the likely weather condition for the period. This informs observers as to where the sky will be clear for viewing the eclipse. Table 5 shows the mean weather conditions in March 2006 at strategic eclipse observatories as a guide to the choice of a place at the time of eclipse magnitude along the track. The critical data are length of sunshine and cloud pattern which determine the probability of seeing the eclipse.

Table 5: Weather Determinants of Clear Eclipse Observation in Africa on 29/3/06 Cloud: percent lrcqucncv of. ..

Location

Latitude

Long

Sunshin e (hours

Probabi

Percent of possible sunshine

A

B

C

D

Abidjan Bouakc Ghana Accra Ada 110 Kumasi Takoradi Tamale Togo

5.25 7.70 5.60 5.78 6.60 6.72 488 9.50

-1,67 063 0.47 -1.60 -1.77 -0.85

6.9

Atakpame

7.58

1.12

6.9

Lome Manzo Nairruouzou

6.17 10.37 9.77

Sokode Tablicbo Benin Bohicon Cotonou Kandi Parakou Save '\igeria ( IUStiU

lhadan

xxxxxx xxxxx

XXXXX

Percent obs with of obstructi ns to o visibility XXXXX

XXXX

XXXXX

...2 1.1

2.3

3.0 3,5

Ohals with TRWaat

eclipse

eclipse time

eclipse time

xxx -3.-13 -5.00

Percent of

Obs with Rain at

XXX

Ivory Coast

Percent of

litvof seeing

7 ..• 6.5

61 5 .•

1.1 1 .•. 3

28.9 2 .•. 7

61.6 52.3

8.-1 8.6

36

57

3.-l

15.4 20.3 32.1 12.6 29.6 2 .•. Togo 7

79.2 71.6 55.6 83.2 66.1 .• 6.8

2,0 2.7 2.5 0 1.7 2.6

3 .• 37 .• 6 3 .• 39 55

0.8 2.7 0 0 2.6 1.2

1.6 2.7 0

56 60 67

5.4 9,9 .•. 2 2.6 260

2.6 1.2

1 .•. 3 4, I 9,9 7,3 1.8 56.3

57

5.4

10.5

786

56

'1

0,7

0.2

85

0.9

128

30.1 14.6 15.3 1.6

15.5 23.2 13.3 1 .•. 2 2.3 08 15.2 8,4 3,9

82,6 51.8 60,6 68.2 78.9

3.6 2.7 1.5 3.1 5.3

30 5 .• .• 6 .• I 31

2.5 0,3 1.5 0.7 1.2

2.1 0.9 1.0 0.5 2.5

3.1 16.-1 8,5 13.9 0,9

92.6 9-1.4 83.6 8-1.7 88.0

5.1 48 1.1

25 2 .• 31

3.9 8.1

30

0.6 2.9 0.7 1.0 0.6

1.0 2,7 0,2 0,2 0.-1

1.2 2,5 36.4 13.0 4.-1

9.5 1.3

78.-1 9 .•. 8

I. .• 2,6

37 26

0

0

569

7.-1 8.2

61 68

8.98 6.58

1.25 0.-12 1.10 1.15 1.50

7.6

63

7,17 6,35 11.13 9.35 8.03

2,07 2,38 2,93 2.62 2.-17

6,6 7,2 84

55 60 70

7.1

59

0 0 0 3.1 0

12.17 7 ..• 5

6.70 .•. 90

6,3

53

10.8 1.3

....

-,-

25

1.1

0

Kaduna Kano Lazos Sakata

Zaria Nizer

10.48 12.05 6.45 13.02 ILl3

7.42 8.53 3.40 5.25 7.68

8.6 8.6 6.4 9.1

72 72 53 76

7.98 13.35 5.25 7.83 2.12 8.98

9.5 9.7 8.9 8.7 8.5 8.8

79 77 74 72 70 73

20.85 9.5 19.17 9.9

79 82

23.33 20.07 22.63 16.55 23.92

9.5 7.9 6.6 7.6

79 66 55 64

14.5

25.4

5Ll

25.2 17.1

26.4 40.4

37.9 10.4 29.5 13.0

3L20 31.88 30.13 25.48

29.85 8.7 25.18 9.0 3157 8.9 29.00

73 75 74

15.6 385 31.0 59.2

18.4 17.7 3Ll 35.2

60.0 36.9 33.5 5.6

3L30

27.2

69

Asadez

16.97 Bilrna 18.55 Birni-N'konni 13.80 Maradi 13.47 Niamey 13.50 Zinder 13.80 Chad Abeche 13.85 Faya-Largeau 18.00 Libya AI Kufrah 25.48 Benzhazi 32.10 Darnah 32.82 Surt (Sirte) 31.20 Tobruk 32.10 Egypt Alexandria As Sallum Cairo Dakhla (Oasis) Marsa Matruh

8.2

N.B. A = Clear B = Scattered

C = broken

1.2 9.9 5.6

20.0 33.3 15.7

71.8 7.1 54.3 2.5 76.4 7.2

33 46 35

1.0 1.0 5.7 0 i.:

L7 5.4 0.0 0.2 0.0 2.1

34.7 33.9 13.6 15.2 40.4 14.8

62.4 59.9 83.7 79.7 57.1 79.6

41 44 30 31 42 32

0.2 0.5 0.4 0.4 0.6 0.4

1.2 0.8 2.7 4.9 2.5 3.5

0 2.3 0 0

2.3 59.3 47.8

0 0 0 0 0.2 0

44.3 41.7 6Ll 57.2 53.8 49.4

0.4

2.1

53 52

6.8 5.0 35 3.1

0.3 0

33.8 9.3

43 60 61 85

3.5 1.9 2.5 0

0 0 0 0