by Mark Wicks
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 thecourse of his investigations on the site of the ancient city of Nippur,made extensive excavations, and dug down and down through the ruinsuntil he had penetrated through those of no less than sixteen differentcities, which, at various times, had been built one over the other. Heunearthed 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 tocontain a complete system of philosophy, science, and religion, andproved that those ancient people knew many things about astronomy, andin some of the fundamental matters would not have much to learn fromastronomers of the present day. These tablets contained, amongst otherthings, records of observations of Mars! It is claimed that Chineserecords go back to a still more remote date.
Since the discovery of the telescope our knowledge of Mars has graduallyextended, and its general surface configuration is now well known to allstudents of the planet.
_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, thusthis map completes the circuit of the Globe of Mars.]
The polar snow-caps were early depicted on drawings, also some of thedark areas; especially the striking one which has been known as theKaiser Sea and the Hour Glass Sea, but is now usually termed SyrtisMajor. It has an outline somewhat resembling that of India; and, if weinclude the southern portion, it is nearly as large in area.
Our maps of Mars are now practically uniform as regards the naming ofthe places marked upon them. Formerly this was not so, as each countryhad its own map and the places marked thereon were named after differentastronomers, and usually after those belonging to the country in whichthe map was prepared. Much confusion arose from this practice, becausethe same spot on Mars might have a different name on each map; thus itwas difficult to identify any particular spot when only the name wasknown.
Some international jealousy also arose owing to the patriotic desire ofobservers to identify particular spots upon Mars with the names of thegreat men of their own country.
To remove this cause of friction and misunderstanding a system has nowbeen almost generally adopted of giving classical names to Martianmarkings. Some of these are of portentous length and strange spelling,but still the adoption of a uniform nomenclature has been a greatconvenience to observers and others who have occasion to use or refer tothe maps.
On looking at a complete chart of the planet it will be seen that thelargest area of dark patches (which are believed to be areas capable ofsupporting life) is situated in the southern hemisphere, and thatseveral of these are wedge-shaped, with the points trending northward.On the earth it is just the opposite, the largest area of land being inthe 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 remaining50,000,000 square miles land.
Mars has a surface area of about 56,000,000 square miles, about35,000,000 square miles being desert, and the remaining 21,000,000square miles land which may be habitable, as most of it is covered withvegetation. There are no large areas of water anywhere upon Mars. Thiscalculation, however, makes no allowance for the lines of vegetationwhich cross the desert, and contain canals, and, with the oases, mayhave a very large population.
From the 50,000,000 square miles of land upon the earth must be deductedthe very large areas which are frozen during the greater part of theyear, and also the large areas which are deserts or bare rocks. Thiswould probably bring down the really habitable area to about 30,000,000square miles.
Making a similar deduction in the case of Mars, but remembering thatmore of the regions near the poles would be habitable during part of theyear than is the case on the earth (as there is practically no permanentglaciation and the temperate zones extend nearly to the poles) thehabitable area would be reduced to, say, 15,000,000 square miles.
It will thus be seen that although the total surface area of Mars isonly rather more than one-quarter of that of the earth, the area of itshabitable 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 sounfavourably with the earth as is usually thought, especially when it isremembered how small a proportion of the earth's area is reallypopulated.
Were it not for the great eccentricity of the planet's orbit, theseasons upon Mars would be very much the same in the different zones asthey are on our world, as the inclination of the planet's equator isonly very slightly less than that of the earth. According to the latestdetermination, the inclination in the case of Mars is 23 deg. and 13'.
As the Martian year is nearly twice as long as ours (being 668 Martiandays, which are equal to 687 of our days) the seasons are of courseproportionately longer in duration. The eccentricity of the orbit,however, causes a much greater difference between the lengths of summerand 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 to372 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 ofthe year is 76 days longer than in the northern hemisphere.
On the earth the winter portion of the year is seven days longer in thesouthern hemisphere than it is in the northern hemisphere.
For this reason, our south polar snow-cap is larger than the north polarcap; and we should naturally expect to find a similar condition uponMars, only greatly accentuated. Astronomical observation shows that thisis the case, for while the northern snow-cap on Mars attains a maximumdiameter of slightly under 80 deg., the southern snow-cap attains amaximum diameter of over 96 deg. The snow-caps are not perfect circles,but irregular in shape, and are, moreover, not exactly opposite to eachother.
Notwithstanding its much greater area the southern snow-cap melts to agreater extent than the northern snow-cap does, owing to the intensityof the heat at the melting period. The northern snow-cap usually meltsuntil the diameter is reduced to about 6 deg., whilst the much largersouthern cap may be reduced to about 5 deg. In the year 1894 itdisappeared entirely! The summer must have been unusually hot.
So far as can be gathered from the records of our whaling and polarexpeditions, it would appear that our north polar snow-cap is from 20deg. to 30 deg. in diameter when at the minimum; whilst the southernsnow-cap is nearly 40 deg. in diameter when smallest.
* * * * *
We had arrived upon Mars on the 24th of September 1909, according toterrestrial reckoning; but according to the Martian date it was then the26th of June in the southern hemisphere, where Sirapion, ourlanding-place, is situated. The season was, therefore, midsummer, andas Sirapion is in latitude 25 deg. south and in the sub-tropical zone,the temperature was fairly high. The mornings were much more clear andbrilliant than those on our earth; the warmth and general "feel" of theair at that time reminding me very much of what it is like in the southof England between seven and eight o'clock on a hot sunny day. Those whoenjoy an early morning walk know how delightful and exhilarating itbecomes towards that time. There is neither chilliness nor uncomfortableheat; one feels a delightful sense of freedom and that it is good to bealive. This is really the best and most enjoya
ble time on a summer'sday. On Mars there was rather more warmth but a greater sense ofexhilaration. Of course, from near noon to about 3 P.M. it was muchwarmer.
Usually a lovely rosy effulgence is seen in the atmosphere in themornings and evenings. As a rule, sunrise and sunset effects are muchmore ethereal and more beautiful than those on the earth, the tintsbeing more delicate and the whole appearance of the sky less broadlymarked. It is as the difference between the crude broad effects of acoloured poster and the delicate effects of a highly-finished painting.
What, in our sunsets, would appear a deep golden colour appears on Marsas a delicate pale gold, merging into bright silver. What with us is acarmine or deep rose, in Martian skies becomes a beautiful rose-pink;whilst the darker, or Indian, red seen for some time at the latterperiod of our sunsets is carmine in the Martian sky, and Indian red onlyappears just at the last.
These tints are seen when the skies are of their normal clearness, butafter the occurrence of a great sand-storm in the desert and the upperair has become filled with fine sand particles, the Martian sunsets areequal in variety and depth of colour to anything seen on our earthduring the months immediately succeeding the Krakatoa eruption. Thosestrange and intensely coloured sunsets will doubtless be remembered bymy readers who had the good fortune to see them during the many monthswhen they were visible after that great volcanic outburst in the year1883.
Sand-storms have been unusually prevalent on Mars during the presentsummer, passing over large areas of country and obscuring the sun forconsiderable periods; so we have had several phenomenal sunsetsafterwards.
As the time passed on the days became cooler--the evenings beingconsiderably more so than on our earth in August, and twilight was verymuch shorter. Towards the end of the Martian August evening dews beganto be succeeded by slight hoar frosts.
The heat in the tropics is not nearly so intense as on the earth. On theother hand, in the high latitudes near the poles, the summer temperatureis higher than in similar latitudes on the earth, because upon Marsthere is no permanent glaciation except right at the poles.
We have, of course, seen the Martian polar stars. The axial tilt of theplanet being less than that of ours, and in a different direction, andits orbit being inclined 1 deg. and 51' in regard to the earth's orbit,it follows that the poles of Mars must point to a different part of thesky, and a considerable distance from our polar stars.
In the northern hemisphere of Mars the polar star is a small one markedon our maps in the constellation of Cepheus, and it is almost on theboundary between that constellation and Cygnus. The pole star liesnearly in a line joining the brighter stars [alpha] Cephei and[alpha] Cygni.
The south polar star is a small one marked [symbol] in that part ofthe large constellation of Argo Navis which is termed Carnia.
Although the polar stars are very small, they shine more brightly in theMartian skies than the north polar star does to us, and are thereforemore easily seen.