Unlike Mercury and Venus, which are never far from the sun, and can be
seen only for a comparatively short time either early in the morning
or in the evening, and are never very high up in the skies, Mars may
be situated so that it can be seen at any time of the night, and also
at any distance from the sun. When it is in opposition it rises just
as the sun sets, and is then in view all night. At this time it is
nearer, larger, and brighter than at any other time in the particular
revolution it is then making, and, consequently, is in the best
position to be viewed by us that it will have during that revolution.
Oppositions differ, however, in different revolutions, and some show
us the planet more splendidly brilliant than it appears at others. The
oppositions at which Mars shows most brilliant take place, fortunately,
in the summer and early autumn--the seasons which are most agreeable
for outdoor observation. He is then traveling through that region of
the sky, sparse in stars, that lies between Sagittarius and Aries; and,
since the ecliptic there runs rather low in the sky, he can easily be
observed at any time in the night without any neck-breaking postures.
These favorable oppositions occur in the summer because the earth is in
line in the latter part of August with that point in the orbit of Mars
where the planet makes its nearest approach to the sun. Oppositions
never occur when Mars is exactly at that point; but they do occur when
he is very near it, and at such times we see him in his greatest glory.
This happens once every fifteen or seventeen years. But at any summer
or early-autumn opposition Mars is not very far from this nearest point
to the sun, so that at any oppositions during these seasons he is very
brilliant and almost as bright as when he is at his best.
The earth is in line in the winter with that part of Mars’s orbit which
carries him farthest from the sun, and at opposition then he is much
less bright than at the summer oppositions. He is at the same time in
those constellations which pass nearly overhead in the sky, and cannot
be quite so comfortably seen at all times in the night as he can be
in the summer. The very best and most brilliant oppositions occur in
the latter part of August or in the early part of September; the
least favorable ones occur in February. The others vary in brilliancy
according to their distance from these favorable and unfavorable dates,
all the summer ones being quite brilliant, and all the winter ones much
less so. At any opposition, though, however unfavorable, the planet is
much nearer to us and much brighter than when in conjunction.
It is worth one’s while, even at some inconvenience, to see Mars at
whatever time he is in opposition, for he is a delight to the observer,
and always notable in the part of the skies through which he is then
passing. There are some aspects of the planet that are so charming
at a winter opposition that it is a positive loss not to have seen
him at such times. He is more isolated and conspicuous in the summer;
but he fits well in that gay company of winter stars that shine more
brilliantly than any others, and we can easily feel something akin to
family pride as we watch him moving so graciously among them.
Mars makes a complete circuit of the skies, and comes back into the
same position with relation to the sun and the earth on an average
every seven hundred and eighty days, which makes his synodic period
longer than that of any other planet. Owing to the great eccentricity
of his orbit, and his consequent unequal motion in the various parts
of it, the synodic period varies as much as thirty-five or thirty-six
days. One cannot say, therefore, without computation of some length,
just exactly how many days will elapse between any two single
oppositions.
For mere purposes of naked-eye observation the variations in the
synodic period of Mars do not make any difference, for the planet is in
view practically all night for many nights before and after opposition,
with changes of brightness too small to be noticed by an untrained
eye. For at least two months at the time of opposition it has almost
the same aspect to us. At that time it is always in the east early in
the evening, and shines all night. For nearly nine months afterward it
is visible and conspicuous in the evening sky, appearing each evening
nearer and nearer to the western horizon, until finally, in a little
more than a year after opposition, it passes behind the sun and becomes
a morning star. But, as it then rises before the sun and passes across
the heavens in the daytime, it is invisible to us. It is pleasant,
however, at such times to know that as the sun passes across the skies
in its daily journey Mars is up there, within a certain distance from
it, making the same journey with it, beaming down upon us with the same
lively light that it shows at night, and could be as well seen at any
time but for the too dazzling rays of the sun.
Mars will be in conjunction in November of this year (1912), and will
not be visible in the evening during 1913 until toward the end of the
year. The next opposition after the publication of this book will occur
in January, 1914. From that time until the following autumn the planet
may be seen in the evening. In 1915 Mars will not be visible in the
evening sky until late in the year. After November it will be in the
east in the evening, rising earlier each evening, until at opposition,
early in 1916, it will rise at sunset and will be visible in the
evening during the entire summer and autumn of that year, but will not
be extraordinarily bright. In 1917 it will be again invisible in the
evening. In 1918 it will be in opposition in the early spring, and will
shine in the evening all the rest of that year. It will not be visible
in the evening in 1919, but will be in opposition again in the latter
part of April, 1920, and will shine in the evening all of that year and
the early part of the next, when it will again disappear from evening
view and will not emerge again until it is nearing a fine opposition
that will take place just at the beginning of the summer of 1922. The
planet will then be in the constellation Scorpio, not far from Antares,
and this will afford an excellent opportunity to see these two ruddy
bodies near together.
In 1924 there will be an exceptionally brilliant opposition, which will
occur during the last week of August, and the planet will then be about
as brilliant as it ever appears, and will be very favorably situated
for observation in the constellation Pisces. We shall then see Mars in
the flame-like phase of his beauty, and he will dominate the evening
sky during the whole of that summer. At oppositions such as this one
Mars is more favorably situated for observation from the earth than any
other heavenly body except the moon.
The next oppositions will take place the last week in October, 1926, in
December, 1928, January, 1931, early March, 1935, the middle of May,
1937; and then we will have two more splendidly brilliant oppositions
in July, 1939, and early October, 1941, respectively.
During the years that Mars does not appear in the evening we need not
be deprived of a sight of the planet if we will look for it in the
morning sky. A few months after conjunction it may be seen as a morning
star, rising shortly before the sun. It rises earlier each morning,
and hence can be seen each morning for a longer time. After its hour
of rising has reached midnight it then passes into the evening sky and
rises earlier each evening until it reaches opposition.
The movement of Mars among the stars, as we see it, is generally toward
the east, and we can see by looking that it changes its place among
the constellations in that direction, going from Aries to Taurus, from
Taurus to Gemini, and so on. On each side of opposition, however, the
planet appears for a few weeks to be moving westward among the stars.
This is the retrograde motion which an outer planet appears to have
when we are overtaking and passing it, and which has been explained in
the chapters on the movements of the planets.