Info

Likely location

Modern circumstances

Description

Ying:

Babylon

Ch'ang-An

Ch'ang-An

Babylon

North Africa

Kuang-ling:

Lo-Yang

Chien-K'ang

Chien-K'ang

Bergamo:

Cordoba:

Constantinople

Kyoto

Novgorod

Salzburg

Vysehrad

Antioch

Vigeois

Kerulen River

Cerrato

Toledo

Montpellier

Arezzo

Cesena

Siena

Reichersberg Stade

Constantinople

Braunschweig

Altaich

Prague

Melk

Coimbra

Rome

Total Total Total Total

Total

Total

Total Total deep partial Annular (~93%) Total

Total Total Total

Partial

Partial

Total

Total

Total

Total

Total

Total

Total

Total

Total

Total

Annular chi ("complete")

chi chi chi

"Dark in daytime"

many stars;four planets seen

Predicted for Claudius chi

"Day became like evening"

chi chi

"Sun hidden from world, then shown again"

"Darkness covered the Earth"

"Sun deprived of light"

chi; "Sun the color of ink"

"Sun perished completely"

"Sun suddenly disappeared"

crescent at south limb

Sun totally obscured

"Sun like a two- or three-day Old Moon" chi

"Sun lost all its strength"

"Sun entirely covered by the Moon"

"Whole body of Sun covered for several minutes"

"Sun covered with darkness;completely black"

"Sun completely obscured;No light"

"No part of the Sun could be seen"

"Sun completely hidden from sight"

"Sun stopped shining"

"Sun lost its light for several minutes"

"Whole Sun eclipsed"

"Complete eclipse"

"Moon covered the whole Sun"

"Narrow circle of light surrounded whole Moon"c a Stephenson and Houlden (1986, p. 208) show the predicted eclipse track, with DT = 2h19!"5, as going through Lo Yang, where the eclipse should have been total.

b This eclipse was observed by a Taoist Master Ch'ang-ch'un who was traveling to Samarkand from China, somewhere on the Kerulen River (extreme northwestern China to northeastern Mongolia).

c This eclipse, reported by Clavius, was total elsewhere along its track;such eclipses are known as "hybrid" eclipses.

Figure 5.11. The ecliptic limits, the angular distances of the Sun from a node of the Moon's orbit, over which distance an eclipse may be seen somewhere on Earth: (a) basic limits. (b) Variations in the ecliptic limits due to slight variations in the inclination of the moon's orbit. Illustration and slide, courtesy Dr. D.J.I. Fry.

Figure 5.11. The ecliptic limits, the angular distances of the Sun from a node of the Moon's orbit, over which distance an eclipse may be seen somewhere on Earth: (a) basic limits. (b) Variations in the ecliptic limits due to slight variations in the inclination of the moon's orbit. Illustration and slide, courtesy Dr. D.J.I. Fry.

are both umbral eclipses corresponding to total or partial conditions and penumbral eclipses, which are also called appulses.11 In the latter case, the Moon enters only the penumbra of the Earth's shadow. The penumbra is a continuously shaded region, darkening gradually into the umbra. In most penumbral eclipses, there is only slight dimming, which could go unnoticed without photometric measurements. Umbral eclipses are far more spectacular, and they may be partial (see Figure 5.13) or total.

11 Cf. the Explanatory Supplement to the Astronomical Ephemeris and Astronomical Ephemeris & Nautical Almanac (1961), p. 257.

During totality, the moon may acquire a coppery, sometimes even crimson, color, especially if it is viewed close to the horizon. The color derives from the scattering of sunlight in the Earth's atmosphere. It is a similar phenomenon to that which produces a red sunset or moonset, but from a different vantage point. The explanation for the visibility of the Moon during lunar eclipses seems to have been advanced for the first time by Kepler (1604, pp. 267-284). Just as the redness and brightness of sunrise/set varies with atmospheric conditions, the brightness and redness of the Moon in the Earth's shadow vary with the atmospheric particle content and the cloud cover at the limbs of the Earth's disk as seen from the Moon. Matsushima et al. (1966) and

Figure 5.12. The basic geometry of a lunar eclipse: Lunar eclipses arise only when the Moon is full and can move into the shadow of the Earth. The geometry is similar to that of a solar eclipse. If the Moon enters the central region, where the Sun is completely blocked by the Earth, the eclipse is said to be umbral; outside this region, the eclipse is said to be penumbral. As is the case for solar eclipses, lunar eclipses may be either partial or total. Illustration and slide, courtesy Dr. D.J.I. Fry.

Figure 5.12. The basic geometry of a lunar eclipse: Lunar eclipses arise only when the Moon is full and can move into the shadow of the Earth. The geometry is similar to that of a solar eclipse. If the Moon enters the central region, where the Sun is completely blocked by the Earth, the eclipse is said to be umbral; outside this region, the eclipse is said to be penumbral. As is the case for solar eclipses, lunar eclipses may be either partial or total. Illustration and slide, courtesy Dr. D.J.I. Fry.

Figure 5.13. The Moon in partial umbral eclipse: RAO archives photo due to Dr. Rita Boreiko.

Matsushima (1967) derived the atmospheric aerosol content following the eruption of the Agung volcano in 1963. Keen (1983) suggested the generalization of this work and hinted that an unusually dark eclipse of 1100, recorded in the Anglo-Saxon Chronicle (Ingram 1912), as well as that of 1588, noted by Kepler, could have been due to such effects.

As is the case for solar eclipses, the Sun must be within the ecliptic limits of the node, when the Moon is opposite the Sun, for a lunar eclipse to occur. The lunar central ecliptic limit, which is the maximum separation in celestial longitude of the mid-shadow point of the Earth from the node, is ~±11°; the partial limit is ~±19°. Beyond these limits, there will be no umbral eclipse. As with the solar ecliptic limits, the actual range varies, so that the major and minor central eclipse limits are, respectively, ±12°15' and ±9°30'. The duration of a lunar eclipse is much greater than that of solar eclipses; if it is central, the total umbral eclipse alone can last 100m, the partial and penumbral immergent and emergent phases ~1h each so that the entire eclipse may last nearly 6h.

Examples of ancient lunar eclipse records, from Stephenson and Clark (1978) and Stephenson and Fatoohi (1997), are given in Table 5.2. The British Museum reference numbers of the tablets with Mesopotamian data are given in the Description column. The translations are by P.J. Huber (1973) and by H. Hunger (Sachs and Hunger 1988, 1989, 1996). The 424 b.c. eclipse record reads as follows:

[Year 41 (Artaxerxes I)], month VI, day 14. 50 deg after sunset, beginning on the north-east side. After 22 deg, 2 fingers lacked to totality. 5 deg duration of maximal phase. In 23 deg toward [west it became bright] 50 deg total duration.

Note the use of "degrees" for time, angle, and angular separation, and "fingers" for small angle measures. This probably refers to the partial eclipse of September 28/29, with magnitude 0.931 (see §5.2.1.3) and umbral contact instants: Tbeg. = 18h28m, Tmax = 20h11m, and Tend = 21h53m, Universal Time (Liu and Fiala 1992, p. 75). Note that Tmax -Tbeg./end = 1.72 hour fi ~51° total duration.

In ancient Greece, observations of lunar eclipses provided important data about the natural world. Aristotle argued that the roundness of the shadow of the Earth at every lunar eclipse implied that the Earth's shape had to be spherical. The relative sizes of the Earth's shadow and the Moon indicated to Aristarchos that the Earth was the larger of the two bodies. Their importance does not end there, however. Lunar eclipses have continued to fascinate and to instruct, down through the ages.

5.2.1.3. Modern Uses of Ancient Eclipse Observations

In addition to date and time and location from which the ancient eclipse was observed, the magnitude of the eclipse (§5.2.1) is another important parameter. This does not indicate the brightness of the Sun or Moon in magnitudes but the maximum extent of the eclipse. This magnitude of a solar eclipse is formally defined as the fraction of the Sun's apparent diameter covered by the Moon at the time of the greatest extent of the eclipse. Similarly, the magnitude of a lunar eclipse is the fraction of the Moon's apparent diameter covered by the Earth's shadow. The magnitude of a total solar eclipse, therefore, is >1, and for an annular or a partial eclipse, it is less than 1; for a total lunar eclipse, it may be greater than 1 because the Earth's shadow is larger than the Moon. The units used to express the magnitude of an eclipse have varied through history. In Chaucer's times, the appar

Table 5.2. Selected records of ancient lunar eclipses.

Modern

Date Viewing location circumstancesa Comments

Modern

Date Viewing location circumstancesa Comments

Table 5.2. Selected records of ancient lunar eclipses.

b.c. 424

Sept.

0 0

Post a comment