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Name

Propontis

Protei Regio

Protonilus

Scandia

Serpentis Mare

Sinai'

Sirenum Mare Sithonius Lacus. . .

Solis Lacus

Styx

Syria

Syrtis Major

Tanai's

Tempe

Thaumasia

Thoth

Thyle I

Thyle II

Thymiamata

Tithonius Lacus.. .

Tractus Albus

Trinacria

Trivium Charontis Tyrrhenum Mare.

Uchronia

Umbra

Utopia

Vulcani Pelagus.. .

Xanthe

Yaonis Regio

Zephryia

FIGURE 2.21. The International Astronomical Union map of Mars based on numerous telescopic observations.

invisible." Lowell also observed that the canals exhibit seasonal darkening in appearance, which he attributed to the development of vegetation as water became available from the polar caps.

The main reason for the interest taken by the general public in Lowell's observations on Mars was his firm opinion that the canals were not natural features but the work of "intelligent creatures, alike to us in spirit, though not in form." In three books, entitled "Mars," published in 1895; "Mars and Its Canals," in 1906; and "Mars as the Abode of Life," 1908, he developed this idea with increasing enthusiasm. Lowell realized that, as seen in the telescope, the canals had considerable width, too wide to be actual waterways. The dark lines, he contended, represented agricultural regions irrigated by water flowing from the Martian polar caps along true canals that are not actually visible. The oases, which like the canals exhibit seasonal variations in appearance, were regarded by Lowell as centers of population surrounded by areas of vegetation.

It is of interest that Schiaparelli, the "father" of the Martian canals, adopted a somewhat equivocal attitude concerning life on the planet. In an article published in 1893, before Lowell started his observations, Schiaparelli said of the canals: "It is not necessary to suppose them to be the work of intelligent beings, and ... we are now inclined to believe them to be produced by the evolution of the planet." Later in the same article, when referring in particular to the double canals, he wrote: "Their singular aspect . . ., as if they were the work of rule and compass, has led some to see in them the work of . . . inhabitants of the planet. I am very careful not to dispute this supposition which includes nothing impossible." However, he went on to say, "The intervention of intelligent beings might explain the geometrical appearance of the gemination, but is not at all necessary for such a purpose." Then, in 1897, perhaps under the influence of Lowell, he wrote: "[The] arrangement [of the canals] presents an indescribable simplicity and symmetry which cannot be the work of chance."

Lowell's views concerning life on Mars created much excitement at the turn of the century. At the present time no scientist believes that there are intelligent beings on the planet. There is no general agreement, however, concerning the canals. Many reputable observers have claimed that they saw them, whereas others have stated equally firmly that, in spite (or because) of excellent seeing conditions, they have been unable to detect the canals. Currently, most astronomers would probably agree that there are linear features on the surface of Mars, but whether they are such long, thin straight lines, as Schiaparelli, Lowell, and others have reported seeing or not is still a matter of controversy. The problem is discussed more fully in chapter VI, but no final solution is offered.

Identification of Martian Features

To the 62 surface features on Mars which Schiaparelli identified and named in 1877, he later added more, as did other astronomers in subsequent years. Although the main aspects of the map of Mars remained unchanged, by the middle of the 20th century nearly 600 features had been named, in accordance with the scheme introduced by Schiaparelli. Unfortunately some newly discovered markings were given different names by different observers. Furthermore, certain named features were obviously temporary; they may have been seen on one occasion but not in later years.

Consequently, the International Astronomical Union appointed a committee to review the naming of the important and permanent aspects of the Martian surface and to prepare a map of the planet. A list was pub-

FIGURE 2.22. Complete circuit of Mars; the longitude of the central meridian is indicated in each case. (Lowell Observatory photographs.)

lished in 1958 of the names and locations, in latitude and longitude, of 128 apparently permanent features. These were given earlier in this chapter and the related map, drawn by G. de Mottoni, is presented in figure 2.21. The latter is a Mercator-type projection which exaggerates the longitudinal dimensions in the higher latitudes. Hence, the map covers the region between latitudes 65° N and 65° S only. The areas of high latitude are shown in the six polar views at the top (south) and bottom (north) of the chart.

The six photographs in figure 2.22, taken at the Lowell Observatory during the favorable opportunity presented in 1941, show a complete circuit of Mars. The latitude of the central meridian is indicated in each case. It is of interest to compare these photographs with the hand-drawn map in figure 2.21.

Recent observations on Mars, especially of its rotation, show that the prime (or zero) meridian, which must pass through both north and south poles, does not coincide with the one postulated by Schiaparelli and that had been in use for some 60 years. The middle of the Meridianii Sinus, to which Schiaparelli assigned 0° longitude, is now at a longitude of 357°. The new zero of latitude and longitude happens to be the northern tip of the western point of Meridianii Sinus.

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