Solar year

“ The beginning and end of a solar year, and the solstices and equinoxes are not marked by any decided natural phenomena, and it is only by long-continued observations of the sun's path among the fixed stars that any tolerably accurate number of days can be assigned to the duration of the year and seasons. ”

“ The civil solar year exists in more varieties than one. The principal variety, conveniently called the Mēshādi year, i.e. “the year beginning at the Mēsha-saṁkrānti,” is the only one that we need notice at this point. The The civil solar year. beginning of it is determined directly by the astronomical solar year; and for religious purposes it begins, with that year, at the moment of the Mēsha-saṁkrānti. ”

“ But let us see what the cycle association between solar spots and terrestrial weather actually is, or rather of what nature it promises to be, for as yet the true nature of the association has not been made out.
It has been found that in a period of about eleven years the sun’s surface is affected by what may be described as a wave of sun-spots. There is a short time—a year or so—during which scarce any spots are seen; they become more and more numerous during the next four or five years, until they attain a maximum of frequency and size ”

“ The number of stellar days in a year is greater by one day than the number of solar days. The stellar day does not follow the variations of light and darkness and therefore does not enter into the calendar. The difference between the actual solar day, which is of slightly varying length, and the mean solar day abstracted from it for the purposes of our clock-regulated time-reckoning has no significance for antiquity. The second unit determined by the sun is the year, the period of a revolution of the earth about the sun. ”

“ In 2other words, though the difference between a single solar year and a single lunar year is more than 11 days, it is possible, by taking a number of years together and reckoning them as lunar years, one or more of them being lengthened by an additional month, to make the whole period very nearly coincide with the same number of solar years. ”

“ Similarly, near the sun’s poles we should find a gradual darkening, as is the case; but from five degrees to thirty degrees latitude, the sun, in its rotation, by reason of the inclination of its axis, passes at every point directly beneath the planets, or within their area of control, and here we find the solar spots in their greatest number, size, and intensity. These sun-spots cross the face of the sun in about fifteen days, and vary in development from year to year, having a cycle of 11.11 years from maximum to maximum. They also have a long cycle of about fifty-six years. ”

“ It is certain that the sun must under such circumstances fall some degrees in temperature each year. In a couple of thousand years the change in temperature would be sufficiently great to affect in the profoundest manner the supply of sunbeams. As, however, we know that for a couple of thousand years, or, indeed, for periods much longer still, there has been no perceptible decrease in the volume of solar radiations, we conclude that the great luminary cannot be regarded merely as a glowing solid globe dispensing its heat by radiation. ”

“ Not only is the Earth’s orbit eccentric in form, but its eccentricity varies within narrow limits; and besides this the orbit itself, as a whole, is subject to a periodical shift of place, from the joint effect of all which changes it comes about that our seasons are now of unequal length, the spring and summer quarters of the year unitedly extending to 186 days, whilst the autumn and winter quarters comprise only 178 days. The sun therefore has the chance of shining for a longer absolute period of time over the northern hemisphere than over the southern hemisphere ”

“ This longer cycle, underlying the sunspot period, alters the time of occurrence of the sunspot maxima in relation to the preceding sunspot minima. He makes out three periods in solar activity, of between three and four years, about eleven, and about thirty-five year respectively. These are related as 1:3:9.
It is clear that the existence of a thirty-five-year period will account for many of the views that have been advanced in favor of a progressive change of climate. A succession of a few years wetter or drier than the normal is likely to lead to the conclusion that the change is permanent. ”

“ A Solar Day is the period of time it takes the Sun to move from any certain meridian of longitude till it returns to the same meridian the next day. Owing to the variable motion of the earth in its orbit, and the obliquity of the ecliptic, the Sun’s path, the solar days are not all of equal length, but as the purposes of social and civil life require a uniform division an average is struck of all solar days in a year, and this is called a Mean Solar Day. ”

“ Let us apply this principle to the solar system, and endeavour to find out whether in that system we have, in relation to the heat thereof, either a cycle of operations or a reversible cycle. We have again to consider the sun as the source of all light and heat in the solar [118] system, radiating forth on every side, year by year, the countless units of heat which go to form the continuance of all planetary life and existence. One of the problems that has confronted scientific men for many years is this, Where does the sun get its supply of heat from? ”

“ We have here another periodic variation, which runs its complete course in a period of a year, and it is easy to see that this variation must have a marked effect on the warming of the earth, the long days and great altitudes of summer producing the greater warmth of that season, while the shorter days and lower altitudes of December, by diminishing the daily supply of solar heat, bring on the winter's cold. ”

“ In addition to this the axis of the earth is continually changing in direction by reason of solar attraction at the equator. This shifting, as explained in the astronomical section, is very slight every year, and in the course of 24,000 years the conditions of the seasons will have completely changed round and back again,—for the northern and southern conditions will be reversed in our hemisphere. Day and night come twenty minutes earlier every year. We are now nearer the sun in winter as shown in diagram (page 497) ; when we change we shall be nearest the sun in summer and farthest in winter. ”

“ The solar impulse which produces these effects tends to precede the terrestrial exhibit which depends upon the solar impulse by some months, possibly by a year under certain conditions, and this anticipation of course promises an opportunity to develop what may become a rational ground for a seasonal forecast for terrestrial weather. ”

“ There is a solar equinoctial, so to speak, just as there is a terrestrial equinoctial in which the sun crosses the line twice each year, and the meteorological disturbances faintly shown on the earth at such times are vastly increased on the sun, and rendered far more complex by the interaction of many planets upon the sun, instead of a single sun upon each planet. ”

“ The solar clock records daily time at too frequent intervals to be of any practical value, and in the tropics at all events the variations in its apparent rising and setting at different times of the year are too slight to be of much practical importance unless a certain degree of culture has been attained. ”

“ The mistake evidently is in making the 25th instead of the 24th, the date of the vernal equinox in the time of Cæsar, consequently a difference of four days instead of three from Cæsar to the Council of Nice.
I.—PAGE 59.
The concurrence of the solar and the civil year was restored by Gregory in 1582, or 1600 is the same in computation; but the discrepancy between civil and solar time is 11 minutes and 10.38 seconds every year, which in 100 years will amount to 18 hours, and 37.3 minutes; reckoned in round numbers 18 hours, and is represented on the chart, hours behind time 18. ”

“ Answer.—Four correct “noon-marks” are made in a year, on the following days: Dec. 24, April 15, June 14, and Sept. 1. Owing to the inclination of the earth’s axis and its unequal movement in its orbit, solar days vary in their length. The average solar day corresponds to the twenty-four hours of our clocks, which keep what is called mean time. ”

“ Twice in the course of the year the earth passes through the plane of the solar equator. During these periods a minimum of solar dust trickles down upon the earth, and that period is characterized by a larger number of polar lights which is distinguished by a higher elevation of the sun above the horizon. ”

“ The eleven-year periodicity is admittedly connected with variations in the solar activity, but there are other cycles which are completely independent of such variations, such as, for instance, the annual variation undergone by all meteorological elements, which depends entirely on the inclination of the earth’s axis. ”

“ They increase progressively in every year; whereas the Dominical letters have a crab-like retrogressive progress, which impedes facility of practice. 3. The rationale of the solar epacts is more easily explained and more readily understood: they are the accumulated odd days short of a complete week; consequently the accumulation must increase by 1 in every year, except in leap years, when it increases by 2 ”

“ The sky here is so pure and clear in our summer that it would be a shame to neglect such an opportunity of making experiments on heat, and accordingly I have been occupied in the December solstice in determining the constant of solar radiation, that is to say, the absolute quantity of heat sent down to the earth’s surface from the sun at noon, or at a vertical incidence. ”

“ While all adolescent suns do not pass through a pulsating stage, at least not visibly, when looking out into space you may observe many of these younger stars whose gigantic respiratory heaves require from two to seven days to complete a cycle. Your own sun still carries a diminishing legacy of the mighty upswellings of its younger days, but the period has lengthened from the former three and one-half day pulsations to the present eleven and one-half year sunspot cycles. ”

“ But the inclination of the equator to the ecliptic, that is, of the earth's plane of daily rotation to that of its annual revolution, necessitates seasons. Each pole must be alternately turned to and away from the sun every year. Each hemisphere, therefore, must have alternately its spring, summer, autumn, and winter. But if the earth's orbit were exactly circular, these seasons would be of equal duration, and the distance from the sun no greater in one than in another. ”

“ It may here be stated as a note by the way that the circumstances under which the Sun first shows itself after it has risen above the horizon has some bearing on the probable character of the weather which is at hand. When the first indications of day-light are seen above a bank of clouds it is thought to be a sign of wind; but if the first streaks of light are discovered low down, that is in, or very near the horizon, fair weather may be expected. ”

“ We are certainly not going so far as to say that any connection has been definitely established between a season of exuberant sun-spots and a season remarkable for excessive warmth, but, as we know that there is a connection between the magnetic condition of the earth and the state of solar activity, it is by no means impossible that climate and sun-spots may also stand in some relationship to each other. ”

“ As, now, the temperature of the sun in its outer portion has been estimated at from 6000° to 7000°, the sun should have cooled completely within historical times. And though the interior of the sun most probably has a vastly higher temperature than the outer portions which we can observe, we should, all the same, have to expect that the solar temperature and radiation would noticeably have diminished in historical times. ”

“ On a really excellent day more may be sometimes detected than during several weeks when the atmosphere is only moderately favourable. The observations, being of a critical nature, should not be103 attempted in winter, when the Sun is low. I have frequently secured fine views of the delicate structure of the solar surface between about 8 and 9 A.M. in the summer months; and this is often a convenient time for amateurs to snatch a glimpse, before going to business. ”

“ Thus the daily difference between the movement of the sun and of the stars leads the sun back very nearly to conjunction with the same star as it was twelve months earlier, and gives us the cycle of the year. The slight difference in the sun's position relative to the stars at the end of the year, finally leads the sun back to the same star at the same time of the year, viz., at the spring equinox, and gives us the great precessional cycle of 25,800 years. ”

“ Speaking loosely, it may be estimated that at the sea-level, in fair weather, neither excessively moist nor dry, about thirty per cent, of the solar radiation is absorbed when the sun is at the zenith, and at least seventy-five per cent, at the horizon. ”

“ They have been apt to forget that, as every world in our own system has its period of life, short by comparison with the entire duration of the world, so each solar system, each system of such systems, may have its own life-bearing season, infinitely long according to our conceptions, but very short indeed compared with the entire duration of which the life-bearing season would be only a single era. ”

“ The heat of the sun is known to be variable, and the eleven years' period of sun-spots has recently attracted much attention as producing appreciable effects on the seasons. There may possibly be longer cycles of solar energy, or the sun may be liable, like some variable stars, to paroxysms of increased energy. ”