Each solar year then--and these are the years we usually reckon by--the equinox is at a point fifty seconds of arc to the east on the zodiac, an effect which is known by the name of the precession of the equinoxes.
To ascertain if there be any such to which they point, we must throw back the heavens to their position in the days of the Egyptians, because, as we have seen, the precession of the equinoxes alters the meridian altitude of every star.
But he did not give up the excentrics and epicycles for the explanation of the irregular motions of the planets, and certain imaginary variations in the precession of the equinoxes and the obliquity of the ecliptic.
There is another equally important and instructive result of this precession of the equinox.
On account of the precession of the equinoxes, as explained in the last chapter, the time at which the sun has any particular position with respect to the stars, grows later year by year in relation to the equinoctial points.
This is what we mean by the precessionof the equinoxes.
Its movement we see in the heavens in the precession of the equinoxes.
But there was already recognised as in existence a peculiar movement which explained theprecession of the equinoxes.
He went much farther: he made the precession of the Equinoxes depend upon this flattening; but he did not furnish its mathematical demonstration.
But even with this reservation the same objection applies to assigning, this as the sole or principal cause of Ice Ages, as to precession alone, viz.
We have already seen that of such causes there is none which appears feasible except Croll's theory of the effects of precession combined with high eccentricity.
This star is not always the same on account of the precession of the equinoxes, and Alpha Draconis supplied the place of the present pole-star about 3440 B.
As precession now favours the northern hemisphere, which is warmer than the southern in corresponding latitudes, it might be thought at first sight that this was the cause of the glacial period.
In fact it is only when combined with periods of high eccentricity of the earth's orbit, according to Croll's theory, that precession can pretend to have any claim to be an important factor in the production of glacial periods.
Neither could the precession of the equinoxes have been of itself a principal cause, for here also the limit of time negatives the supposition.
This balancing, which has been compared to that of a top when about to cease spinning, produces the movement known as the precession of the equinoxes.
In support of this estimate Mr. Hopkins puts forward another argument, based upon the precession of the equinoxes.
It is this retrograde evolution, in which the terrestrial axis describes round its own centre that revolution round a double conic surface, which is known as the precession of the equinoxes.
Two thousand years ago, the Ram was regarded as the symbol of spring; but owing to the secular movement of the precession of the equinoxes, the Sun is no longer there on March 21: he is in the Fishes.
I must first tell you this flattening of the poles is the cause of the precession of the equinoxes; that is to say, why every year the vernal equinox comes a day sooner than it would if the earth were perfectly round.
That comes from the precession of the equinoxes, of which I shall speak soon.
The precession of the equinoxes is a slow but continual shifting of the equinoctial points, from east to west.
The changes produced by theprecession of the equinoxes, in the apparent places of the circumpolar stars, have led to some interesting results in chronology.
He formed very accurate estimates of the obliquity of the ecliptic and of the precession of the equinoxes.
I shall conclude what I have to say at present, respecting the motion of the earth around the sun, by adding a few words respecting the precession of the equinoxes.
It must be observed, however, that this mode of conceiving of the precession of the equinoxes is purely imaginary, and is employed merely for the convenience of representation.
In other words, we may say that one-third of the movement of precession is due to the sun, and two-thirds to the moon.
The actual intensity of the force itself augments in the inverse square of the distance, and hence the capacity of the attracting body for producingprecession will, for a double reason, increase when the distance decreases.
If the earth were a perfect sphere, precession would be inexplicable.
We are therefore forced to seek for an explanation of precession in the fact that the earth is not a perfect sphere.
The phenomena of precession and nutation depend on movements of the earth itself, and not on movements of the axis of rotation within the earth.
It is affected by the motions of Precessionand Nutation, of which the former has been known since the time of Hipparchus.
This is not the case at present, owing to the precession of the equinoxes.
Owing to the precession of the equinoxes, the sidereal year is not the same as the solar year, being about 20 minutes longer.
It is obvious that during this long cycle the precession of the equinox must have completed seven revolutions.
Alfred Jeremias gives very forcible reasons for believing that the ancient Babylonians were acquainted with the precession of the equinoxes.
Sidenote: The precession of events as seen in space.
Realise to yourself, my friend, this presentation of an actual fact, for it is of importance to you to comprehend the precession of the waves of light and to understand the essential nature of this undoubted truth.
This phenomenon is called the precessionof the equinoxes.
When this moon acted on the earth, in conjunction with, or in opposition to the sun, variations in the earth's motion would be occasioned, and these variations produce what is called the precession of the equinoxes.
He sees the earth rotating against the direction of the hands of a watch, and he finds that it precesses with the hands of a watch, so that spin and precession are in opposite directions.
But it revolves once about its centre in twenty-seven solar days, eight hours, and it will no longer swing like a ship in a ground-swell, but will get a motion of precession opposed in direction to its own revolution.
The last two statements come to this:--When the forces acting on a spinning body tend to make the angle of precession greater, the precession is in the same direction as the spinning, and vice versa.
The precession of the earth is then of the same nature as that of a gyrostat suspended above its centre of gravity, of a body which would be stable and not top-heavy if it were not spinning.
When the gyrostat is not spinning, the ship vibrates slowly when put out of equilibrium; when the gyrostat is spinning the ship gets a motion of precession which is opposite in direction to that of the spinning.
Indeed it is because of this that we have the word "precession," which we now apply to the motion of a top, although the precession of a top is in the same direction as that of the spin.
If this rule is right, we see at once why precession takes place.
In fact theprecession of the earth is of the same nature as that of this large gyrostat (Fig.
Mathematical Tracts on Physical Astronomy, the Figure of the Earth, Precessionand Nutation, and The Calculus of Variations.
It is determined by the movement of the sun known to astronomers as precession of the equinox, by which the sun moves through one of the signs of the Zodiac in about 2100 years.
He devoted much time and study to the problem of the obliquity of the ecliptic, to the precession of the equinoxes,[127] and to the determination of the latitude and longitude of places.
An important consequence of the precession of the equinoxes lies in the fact that the zodiacal constellations do not agree with the signs with which they coincided in ancient times, i.
As to how much he thought should be added to or subtracted from the longitude of the fixed stars each year, to the end of taking due note of the precession of the equinoxes, he copied Plancius literally.
The year 1600 was selected as the normal year for recording the position of the stars, and a statement is made noting the corrections becoming necessary by reason of the precession of the equinoxes.
When in the state of extreme ellipticity, the precession of the equinoxes will cause the hemispheres in turn each to have their winter and summer alternately near and far from the sun.
Thirdly, the variations in the eccentricity of the earth's orbit, combined with the precession of the equinoxes and the rotation of the apsides, may be regarded as operative.
The Hindus, however, have disregarded precession in connexion with their calendar from the time (A.
It is not that which astounds us, for the axis of the earth has an imperceptible movement in about twenty-six thousand years which occasions the precession of the equinoxes.
Not even the precessionof the equinoxes will terrify him.
