The Martian Seasons
:
To Mars Via The Moon
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
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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.
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 deg. 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 deg., the southern snow-cap attains a
maximum diameter of over 96 deg. 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 deg., whilst the much larger
southern cap may be reduced to about 5 deg. 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
deg. to 30 deg. in diameter when at the minimum; whilst the southern
snow-cap is nearly 40 deg. 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 deg. 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 noon to about 3 P.M. it was much
warmer.
Usually a lovely rosy effulgence is seen in the atmosphere in the
mornings and evenings. As a rule, sunrise and sunset effects are much
more ethereal and more beautiful than those on the earth, the tints
being more delicate and the whole appearance of the sky less broadly
marked. It is as the difference between the crude broad effects of a
coloured poster and the delicate effects of a highly-finished painting.
What, in our sunsets, would appear a deep golden colour appears on Mars
as a delicate pale gold, merging into bright silver. What with us is a
carmine or deep rose, in Martian skies becomes a beautiful rose-pink;
whilst the darker, or Indian, red seen for some time at the latter
period of our sunsets is carmine in the Martian sky, and Indian red only
appears just at the last.
These tints are seen when the skies are of their normal clearness, but
after the occurrence of a great sand-storm in the desert and the upper
air has become filled with fine sand particles, the Martian sunsets are
equal in variety and depth of colour to anything seen on our earth
during the months immediately succeeding the Krakatoa eruption. Those
strange and intensely coloured sunsets will doubtless be remembered by
my readers who had the good fortune to see them during the many months
when they were visible after that great volcanic outburst in the year
1883.
Sand-storms have been unusually prevalent on Mars during the present
summer, passing over large areas of country and obscuring the sun for
considerable periods; so we have had several phenomenal sunsets
afterwards.
As the time passed on the days became cooler-the evenings being
considerably more so than on our earth in August, and twilight was very
much shorter. Towards the end of the Martian August evening dews began
to be succeeded by slight hoar frosts.
The heat in the tropics is not nearly so intense as on the earth. On the
other hand, in the high latitudes near the poles, the summer temperature
is higher than in similar latitudes on the earth, because upon Mars
there is no permanent glaciation except right at the poles.
We have, of course, seen the Martian polar stars. The axial tilt of the
planet being less than that of ours, and in a different direction, and
its 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 the
sky, and a considerable distance from our polar stars.
In the northern hemisphere of Mars the polar star is a small one marked
on our maps in the constellation of Cepheus, and it is almost on the
boundary between that constellation and Cygnus. The pole star lies
nearly 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 of
the large constellation of Argo Navis which is termed Carnia.
Although the polar stars are very small, they shine more brightly in the
Martian skies than the north polar star does to us, and are therefore
more easily seen.