CHAPTER XXIV

THE MARTIAN SEASONS

Our earliest records of Mars date back to a very remote period, viz. 2300 years before the birth of Christ! Professor Hilprecht, in the course of his investigations on the site of the ancient city of Nippur, made extensive excavations, and dug down and down through the ruins until he had penetrated through those of no less than sixteen different cities, which, at various times, had been built one over the other. He unearthed the famous Temple of Bel, together with its great library, consisting of over 23,000 tablets, containing the chronicles of Bel.

When a number of these tablets had been deciphered, they were found to contain a complete system of philosophy, science, and religion, and proved that those ancient people knew many things about astronomy, and in some of the fundamental matters would not have much to learn from astronomers of the present day. These tablets contained, amongst other things, records of observations of Mars! It is claimed that Chinese records go back to a still more remote date.

Since the discovery of the telescope our knowledge of Mars has gradually extended, and its general surface configuration is now well known to all students of the planet.

[Illustration: From a Globe made by M. Wicks Plate XIII

MARS. MAP VI

“Syrtis Major” is seen on the extreme left just below the Equator. “Sabaeus Sinus” is again in view just to the right of the centre, thus this map completes the circuit of the Globe of Mars.]

The polar snow-caps were early depicted on drawings, also some of the dark areas; especially the striking one which has been known as the Kaiser Sea and the Hour Glass Sea, but is now usually termed Syrtis Major. It has an outline somewhat resembling that of India; and, if we include the southern portion, it is nearly as large in area.

Our maps of Mars are now practically uniform as regards the naming of the places marked upon them. Formerly this was not so, as each country had its own map and the places marked thereon were named after different astronomers, and usually after those belonging to the country in which the map was prepared. Much confusion arose from this practice, because the same spot on Mars might have a different name on each map; thus it was difficult to identify any particular spot when only the name was known.

Some international jealousy also arose owing to the patriotic desire of observers to identify particular spots upon Mars with the names of the great men of their own country.

To remove this cause of friction and misunderstanding a system has now been almost generally adopted of giving classical names to Martian markings. Some of these are of portentous length and strange spelling, but still the adoption of a uniform nomenclature has been a great convenience to observers and others who have occasion to use or refer to the maps.

On looking at a complete chart of the planet it will be seen that the largest area of dark patches (which are believed to be areas capable of supporting life) is situated in the southern hemisphere, and that several of these are wedge-shaped, with the points trending northward. On the earth it is just the opposite, the largest area of land being in the northern hemisphere, and the wedge-shaped masses trend southward.

Our earth’s surface comprises an area of about 193,000,000 square miles, of which some 143,000,000 square miles are water, and the remaining 50,000,000 square miles land.

Mars has a surface area of about 56,000,000 square miles, about 35,000,000 square miles being desert, and the remaining 21,000,000 square miles land which may be habitable, as most of it is covered with vegetation. There are no large areas of water anywhere upon Mars. This calculation, however, makes no allowance for the lines of vegetation which cross the desert, and contain canals, and, with the oases, may have a very large population.

From the 50,000,000 square miles of land upon the earth must be deducted the very large areas which are frozen during the greater part of the year, and also the large areas which are deserts or bare rocks. This would probably bring down the really habitable area to about 30,000,000 square miles.

Making a similar deduction in the case of Mars, but remembering that more of the regions near the poles would be habitable during part of the year than is the case on the earth (as there is practically no permanent glaciation and the temperate zones extend nearly to the poles) the habitable area would be reduced to, say, 15,000,000 square miles.

It will thus be seen that although the total surface area of Mars is only rather more than one-quarter of that of the earth, the area of its habitable land, even under its present unfavourable circumstances, amounts to about half of the habitable area of the earth.

Looking at Mars from this point of view, it does not contrast so unfavourably with the earth as is usually thought, especially when it is remembered how small a proportion of the earth’s area is really populated.

Were it not for the great eccentricity of the planet’s orbit, the seasons upon Mars would be very much the same in the different zones as they are on our world, as the inclination of the planet’s equator is only very slightly less than that of the earth. According to the latest determination, the inclination in the case of Mars is 23° and 13’.

As the Martian year is nearly twice as long as ours (being 668 Martian days, which are equal to 687 of our days) the seasons are of course proportionately longer in duration. The eccentricity of the orbit, however, causes a much greater difference between the lengths of summer and winter in the two hemispheres.

* * *

In the northern hemisphere of Mars, spring lasts 191 Martian days; summer, 181 days; autumn, 149 days; and winter, 147 days.

In the southern hemisphere spring lasts 149 days; summer, 147 days; autumn, 191 days; and winter, 181 days.

Thus, in the northern hemisphere spring and summer together amount to 372 days, and autumn and winter to 296 days.

In the southern hemisphere, however, spring and summer have 296 days, whilst autumn and winter last 372 days; so that the winter period of the year is 76 days longer than in the northern hemisphere.

On the earth the winter portion of the year is seven days longer in the southern hemisphere than it is in the northern hemisphere.

For this reason, our south polar snow-cap is larger than the north polar cap; and we should naturally expect to find a similar condition upon Mars, only greatly accentuated. Astronomical observation shows that this is the case, for while the northern snow-cap on Mars attains a maximum diameter of slightly under 80°, the southern snow-cap attains a maximum diameter of over 96°. The snow-caps are not perfect circles, but irregular in shape, and are, moreover, not exactly opposite to each other.

Notwithstanding its much greater area the southern snow-cap melts to a greater extent than the northern snow-cap does, owing to the intensity of the heat at the melting period. The northern snow-cap usually melts until the diameter is reduced to about 6°, whilst the much larger southern cap may be reduced to about 5°. In the year 1894 it disappeared entirely! The summer must have been unusually hot.

So far as can be gathered from the records of our whaling and polar expeditions, it would appear that our north polar snow-cap is from 20° to 30° in diameter when at the minimum; whilst the southern snow-cap is nearly 40° in diameter when smallest.

* * *

We had arrived upon Mars on the 24th of September 1909, according to terrestrial reckoning; but according to the Martian date it was then the 26th of June in the southern hemisphere, where Sirapion, our landing-place, is situated. The season was, therefore, midsummer, and as Sirapion is in latitude 25° south and in the sub-tropical zone, the temperature was fairly high. The mornings were much more clear and brilliant than those on our earth; the warmth and general “feel” of the air at that time reminding me very much of what it is like in the south of England between seven and eight o’clock on a hot sunny day. Those who enjoy an early morning walk know how delightful and exhilarating it becomes towards that time. There is neither chilliness nor uncomfortable heat; one feels a delightful sense of freedom and that it is good to be alive. This is really the best and most enjoyable time on a summer’s day. On Mars there was rather more warmth but a greater sense of exhilaration. Of course, from near

Добавить отзыв
ВСЕ ОТЗЫВЫ О КНИГЕ В ИЗБРАННОЕ

0

Вы можете отметить интересные вам фрагменты текста, которые будут доступны по уникальной ссылке в адресной строке браузера.

Отметить Добавить цитату