A Handbook of Descriptive and Practical Astronomy: Instruments and practical astronomyClarendon Press, 1890 |
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Συχνά εμφανιζόμενοι όροι και φράσεις
adjustment Altazimuth ALTAZIMUTH MOUNTING altitude angle Ångström aperture appear astronomical bands bright lines Catalogue celestial object centre chromosphere circle clock collimation colour comet Contains cycle dark lines declination diameter disc distance dome Double Stars eclipse equator equatorial equatorial mounting equatorial room eye-piece focal length focus Fraunhofer lines glass Greenwich Harvard College Observatory Herschel horizontal hour-circle Huggins hydrogen inches interval lens lenses Lick Observatory light Lockyer longitude lunar magnitude means measure Memoirs R.A.S. meridian Metonic cycle micrometer mirror Month Moon motion mounted nebula object-glass Observatory obtained optical orbit parallax Paris Observatory photographs planet plate polar axis position Pract prism rays reduced reflector refraction refractor Right Ascension ring satellites screw Secchi's seen sextant shutter sidereal slit sodium solar spectrum spectra spectroscope spot star otherwise called stars observed Sun's Tables telescope Transit Instrument tube vertical violet wave-lengths whilst wires zenith
Δημοφιλή αποσπάσματα
Σελίδα 541 - When a straight line standing on another straight line makes the adjacent angles equal to one another, each of the angles is called a right angle ; and the straight line which stands on the other is called a perpendicular to it.
Σελίδα 15 - ... is, become indistinct by a very slight motion on either side of it. A proper test-object must be chosen : the Moon is too easy ; Venus too severe, except for first-rate glasses ; large stars have too much glare; Jupiter or Saturn are far better; a close double star is best of all for an experienced eye ; but for general purposes a moderate-sized star will suffice. Its image in focus, with the highest power, should be a very small disc, almost a point, accurately round ; without
Σελίδα 189 - His instrument consists of a wedge of shade glass of a neutral tint inserted in the field of view of the telescope, and movable so that a star may be viewed through the thicker or thinner portions at will. The exact position is indicated by means of a scale. The light of different stars is measured by bringing them in turn to the centre of the field, and moving the wedge from the thin towards the thick end until the star disappears. The exact point of disappearance is then read by the scale.
Σελίδα 184 - H ; both the prisms and the lens are fastened in this tube. K is a small right-angled prism, covering half the slit, by the aid of which light may be seen reflected through the circular aperture in front of it. In this manner a comparison may be made with the spectra of metals or gases. The reflecting prism, with the ring to which it is attached, can be instantly removed, and the whole length of the slit used if desired. DD is a ring milled on the edge ; on turning this round, both edges of the slit...
Σελίδα 451 - Subtract the epact from 57, divide by 7, and keep the remainder, or 7, if there be no remainder. XV. To XIII. add VII., the dominical number, (and 7 besides, if XIV. be greater than VII.,) and subtract XIV., the result is the day of March, or if more than 31, subtract 31, and the result is the day of April, on which Easter Sunday falls.
Σελίδα 159 - Subtract the Sun's declination from 90«, when the latitude and declination are of the same name, or add it to 90*, when they are of contrary names ; and the sum, or remainder, will be the Sun's polar distance. , 3. Add together the Sun's polar distance, the latitude of the place, and the altitude of the Sun; take the difference between half their sum and the polar distance, and note the remainder.
Σελίδα 152 - It is erected perpendicular to the plane of the sextant and parallel to the index glass when the zero of the vernier coincides with the zero of the arc.
Σελίδα 41 - With respect to the practical working of the illumination, I will briefly say that it has proved a complete success in every respect. Any object that can be seen under any circumstances, however faint, can be well and accurately measured. There is no such thing as a star too faint for measurement, if it can be seen at all. A very feeble light is sufficient to illuminate the wires perfectly for any object.
Σελίδα 350 - ... due to gravity. II. The spectra of all bodies depend upon the heat of the meteorites, produced by collisions, and the average space between the meteorites in the swarm, or in the case of consolidated swarms upon the time which has elapsed since complete vaporization.
Σελίδα 548 - Nodes (nodus, a knot) are those points in the orbit of a planet or a comet where it intersects the ecliptic. The ascending node...