Outlines of Astronomy - John Frederick William Herschel - Google книги

Книги

Зображення сторінки

CONTENTS.

PART I.

General notions. Apparent and real motions. Shape and size of the Earth.

The horizon and its dip. The atmosphere." Refraction. Twilight.

Appearances resulting from diurnal motion. From change of station in

general. Parallactic motions. Terrestrial parallax. That of the stars

insensible. First step towards forming an idea of the distance of the stars.

Copernican view of the Earth's motion. Relative motion. Motions partiy

real, partly apparent. Geocentric astronomy, or ideal reference of pheno-

mena to the Earth's centre as a common conventional station .

Terminology and elementary geometrical conceptions and relations. Ter-

minology relating to the globe of the Earth—to the celestial sphere.

Celestial perspective

Of the nature of astronomical instruments and observations in general.

Of sidereal and solar time. Of the measurements of time. Clocks, chro-

nometers. Of astronomical measurements. Principle of telescopic sights

to increase the accuracy of pointing. Simplest application of this princi-

ple. The transit instrument. Of the measurement of angular intervals.

Methods of increasing the accuracy of reading. The vernier. The

microscope. Of the mural circle. The Meridian circle. Fixation of

polar and horizontal points. The level, plumb-line, artificial horizon.

Principle of collimation. Collimators of Rittenhouse, Kater, and Benzen-

berg. Of compound instruments with co-ordinate circles. The equatorial,

altitude, and azimuth instrument. Theodolite. Of the sextant and

reflecting circle. Principle of repetition. Of micrometers. Parallel wire

micrometer. Principle of the duplication of images. The heliometer.

Double refracting eye-piece. Variable prism micrometer. Of the position.

Of the figure of the Earth. Its exact dimensions. Its form that of equili-

brium modified by centrifugal force. Variation of gravity on its surface.

Statical and dynamical measures of gravity. The pendulum. Gravity

to a spheroid. Other effects of the Earth's rotation. Trade winds.

Determination of geographical positions—of latitudes-of longitudes.

Conduct of a trigonometrical survey. Of maps. Projections of the sphere.

Measurement of heights by the barometer

OF URANOGRAPIY.

Construction of celestial maps and globes by observation of right ascension

and declination. Celestial objects distinguished into fixed and erratic.

Of the constellations. Natural regions in the heavens. The Milky Way.

The Zodiac. Of the Ecliptic. Celestial latitudes and longitudes. Pre-

cession of the Equinoxes. Nutation. Aberration. Refraction. Parallax.

Summary view of the Uranographical corrections .

OF THE SUN'S MOTION.

Apparent motion of the Sun not uniform. Its apparent diameter also

variable. Variation of its distance concluded. Its apparent orbit an ellipse

about the focus. Law of the angular velocity. Equable description of

areas. Parallax of the Sun. Its distance and magnitude. Copernican

explanation of the Sun's apparent motion. Parallelism of the Earth's

Heat received from the Sun in different parts of the

orbit. Mean and true longitudes of the Sun. Equation of the centre.

Sidereal, tropical, and anomalistic years. Physical constitution of the

Sun. Its spots. Faculæ. Probable nature and cause of the spots.

Atmosphere of the Sun. Its supposed clouds. Temperature at its

surface. Its expenditure of heat. Terrestrial effect of solar radiation 205

Of the Moon. Its sidereal period. Its apparent diameter. Its parallax,

distance, and real diameter. First approximation to its orbit. An ellipse

about the Earth in the focus. Its excentricity and inclination. Motion

of its nodes and apsides. Of occultations and solar eclipses generally.

Limits within which they are possible. They prove the Moon to be an

opaque solid. Its light derived from the Sun. Its phases. Synodic

revolution or lunar month. Of eclipses more particularly. Their pheno-

Their periodical recurrence. Physical constitution of the Moon.

Its mountains and other superficial features. Indications of former

volcanic activity. Its atmosphere. Climate. Radiation of heat from

its surface. Rotation on its own axis. Libration. Appearance of the

Of terrestrial gravity. Of the law of universal gravitation. Paths of pro-

jectiles,-apparent, real. The Moon retained in her orbit by gravity. Its

law of diminution, Laws of elliptic motion. Orbit of the Earth round

the Sun in accordance with these laws. Masses of the Earth and Sun

compared. Density of the Sun. Force of gravity at its surface. Disturb-

ing effect of the Sun on the Moon's motion

257
CHAPTER IX.

OF THE SOLAR SYSTEM.

Apparent motions of the planets. Their stations and retrogradations. The

Sun their natural centre of motion. Inferior planets. Their phases,

periods, etc. Dimensions and form of their orbits. Transits across the

Sun. Superior planets. Their distances, periods, etc. Kepler's laws

and their interpretation. Elliptic elements of a planet's orbit. Its helio-

centric and geocentric place. Empirical law of planetary distances;

violated in the case of Neptune. The ultra-zodiacal planets. Physical

peculiarities observable in each of the planets

OF THE SATELLITES.

Of the Moon, as a satellite of the Earth. General proximity of satellites

to their primaries, and consequent subordination of their motions. Masses

of the primaries concluded from the periods of their satellites. Main-

tainance of Kepler's laws in the secondary systems. Of Jupiter's satel-

lites; their eclipses, etc. Velocity of light discovered by their means.

Satellites of Saturn-of Uranus—of Neptune .

Great number of recorded comets. The number of those unrecorded pro-

bably much greater. General description of a comet. Comets without

tails, or with more than one. Their extreme tenuity. Their probable

structure. Motions conformable to the law of gravity. Actual dimen-

sions of comets. Periodical return of several. Halley's comet. Other

ancient comets probably periodic. Encke's comet-Biela's—Faye's-

Lexell's—De Vico's-Brorsen's—Peter's. Great comet of 1843. Its

probable identity with several older comets. Great interest at present

attached to cometary astronomy, and its reasons. Remarks on cometary

orbits in general

OF THE PLANETARY PERTURBATIONS.

Subject propounded. Problem of three bodies. Superposition of small

motions. Estimation of the disturbing force. Its geometrical representa-

tion. Numerical estimation in particular cases.

Resolution into rect-

angular components. Radial, transversal, and orthogonal disturbing

forces. Normal and tangential. Their characteristic effects. Effects of

the orthogonal force. Motion of the nodes. Conditions of their advance

and recess. Cases of an exterior planet disturbed by an interior. The

reverse case. In every case the node of the disturbed orbit recedes on the

plane of the disturbing on an average. Combined effect of many such

disturbances. Motion of the Moon's nodes. Change of inclination.

Conditions of its increase and diminution. Average effect in a whole revo-

lution. Compensation in a complete revolution of the nodes. Lagrange's

theorem of the stability of the inclinations of the planetary orbits. Change

of obliquity of the ecliptic. Precession of the equinoxes explained. Nuta-

tion. Principle of forced vibrations

THEORY OF THE AXES, PERIHELIA, AND EXCENTRICITIES.

'Variation of elements in general. Distinction between periodic and secular

variations. Geometrical expression of tangential and normal forces.

Variation of the Major Axis produced only by the tangential force.

Lagrange's theorem of the conservation of the mean distances and periods.

Theory of the Perihelia and excentricities. Geometrical representation

of their momentary variations. Estimation of the disturbing forces in

nearly circular orbits. Application to the case of the Moon. Theory of

the lunar apsides and excentricity. Experimental illustration. Applica-

tion of the foregoing principles to the Planetary theory. Compensation

in orbits very nearly circular. Effects of ellipticity. General results.

Lagrange's theorem of the stability of the excentricities .

Of the inequalities independent of the excentricities. The Moon's variation

and parallactic inequality. Analogous planetary inequalities. Three

cases of Planetary perturbation distinguished. Of inequalities dependent

on the excentricities. Long inequality of Jupiter and Saturn. Law of

reciprocity between the periodical variations of the elements of both

planets. Long inequality of the Earth and Venus. Variation of the

epoch. Inequalities incident on the epoch affecting the mean motion.

Interpretation of the constant part of these inequalities. Annual equation

of the Moon. Her secular acceleration. Lunar inequalities due to the

action of Venus. Effect of the spheroidal figure of the Earth and other

planets on the motions of their satellites. Of the tides. Masses of dis-

turbing bodies deducible from the perturbations they produce. Mass of

Moon, and of Jupiter's satellites, how ascertained. Perturbations of

Uranus resulting in the discovery of Neptune

OF SIDEREAL ASTRONOMY.

Of the fixed stars. Their classification by magnitudes. Photometric scale

of magnitudes. Conventional or vulgar scale. Photometric comparison

of stars. Distribution of stars over the heavens. Of the Milky Way or

galaxy. Its supposed form that of a flat stratum partially subdivided.

Its visible course among the constellations. Its internal structure. Its

apparently indefinite extent in certain directions. Of the distance of the

fixed stars. Their annual parallax. Parallactic unit of sidereal distance.

Effect of parallax analogous to that of aberration. How distinguished

from it. Detection of parallax by meridional observations. Henderson's

application to a centauri. By differential observations. Discoveries of

Bessel and Struve. List of stars in which parallax has been detected.

Of the real magnitudes of the stars. Comparison of their lights with that

Variable and periodical stars. List of those already known. Irregularities

in their periods and lustre when brightest. Irregular and temporary

stars. Ancient Chinese records of several. Missing stars. Double stars.

Their classification. Specimens of each class. Binary systems. Revolu-

tion round each other. "Describe elliptic orbits under the Newtonian law

of gravity. Elements of orbits of several. Actual dimensions of their

orbits. Coloured double stars. Phenomenon of complimentary colours.

Sanguine stars. Proper motion of the stars. Partly accounted for by a

real motion of the Sun. Situation of the solar apex. Agreement of

southern and northern stars in giving the same result. Principles on

which the investigation of the solar motion depends. Absolute velocity

of the Sun's motion. Supposed revolution of the whole sidereal system

round a common centre. Systematic parallax and aberration. Effect of

the motion of light in altering the apparent period of a binary star

OF CLUSTERS OF STARS AND NEBULÆ.

Of clustering groups of stars. Globular clusters. Their stability dyna-

mically possible. List of the most remarkable. Classification of nebulæ

and clusters. Their distribution over the heavens. Irregular clusters.

Resolvability of nebulæ. Theory of the formation of clusters by nebulous

subsidence. Of elliptic nebulæ. That of Andromeda. Annular and

planetary nebulæ. Double nebulæ. Nebulous stars. Connection of

nebulæ with double stars. Insulated nebulæ of forms not wholly irregular.

Of amorphous nebulæ. Their law of distribution marks them as outliers

of the galaxy. Nebulæ and nebulous group of Orion-of Argo—of Sagit-

tarius—of Cygnus. The Magellanic clouds. Singular nebula in the

greater of them. The zodiacal light. Shooting stars

OF THE ACCOUNT OF TIME.

Natural Units of time. Relation of the sidereal to the solar day affected

by precession. Incommensurability of the day and year. Its incon-

How obviated. The Julian Calendar. Irregularities at its

first introduction. Reformed by Augustus. Gregorian reformation.

Solar and lunar cycles. Indiction. Julian period. Table of Chrono-

logical cras. Rules for calculating the days elapsed between given Dates.

Equinoctial time.

venience.

I. Lists of Northern and Southern Stars, with their approximate

Magnitudes, on the Vulgar and Photometric Scales

II. Synoptic Table of the Elements of the Planetary System 606-7

III. Synoptic Table of the Elements of the Orbits of the Satellites, so

as they are known

IV. Elements of Periodicai Comets at their last Appearance 611

« Назад Продовжити »