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actual adopted apparent assumed Astronomical average axis binary stars binary systems bright brighter Catalogue chapter circle close companion components computed constant correct corresponding curve definite determined direction discoveries distance double stars eccentricity effect elements ellipse entirely equal equation errors evidence fact figures formulae give given greater increase known later least less light limits lines magnitude mass mean measures method micrometer motion nearly noted object Observatory observed obtained orbit origin pairs parallax percentage periastron period placed plane plates points position position angle possible practically present primary probably published radial velocity range reading reduction referred relation relative represent respectively separation shown spectra spectral class spectrograph spectroscopic binaries spectrum stellar Table taken telescope theory thread tion true unit variable visual binaries
Page 2 - We may conclude with the highest probability (the odds against the contrary opinion being many million millions to one) that stars form a kind of system by mutual gravitation. It is highly probable in particular, and next to a certainty in general, that such double stars as appear to consist of two or more stars placed near together are under the influence of some general law, such perhaps as gravity.
Page 255 - ... Durchmusterung contains 100,979 stars as bright as 9.0 magnitude north of the celestial equator; 5400 of these, or one in 18.7 on the average, have actually been found to be double within the chosen limits. If we add only 200 more pairs the ratio is increased to 1 in 18.03. We may therefore conclude that at least one in every eighteen, on the average, of the stars as bright as 9.0 magnitude in the northern half of the sky is a double star visible with the 36-inch telescope.
Page 228 - The visibility of countless stars is no argument against the invisibility of countless others.
Page 202 - P the period and a the semi.axis major of its orbit, and the units of mass, length and time are respectively, the Sun's mass, the astronomical unit, and the year.
Page 72 - Ü = the position angle of that nodal point which lies between 0° and 180°; that is, the position angle of the line of intersection of the orbit plane with the plane perpendicular to the line of sight. Call this merely "the nodal point", disregarding the distinction between ascending and descending nodes.
Page 169 - L,-\-L2, can be taken as the unit of light and the apparent brightness at any time expressed in terms of this. This leaves the problem with eleven unknown quantities to be determined from the photometric measures. Of these, the period is invariably known with a degree of accuracy greatly surpassing that attainable for any of the other elements, and the epoch of principal minimum can be determined, almost independently of the other elements, by inspection of the light-curve. Of the remaining elements,...
Page 170 - Two spherical stars, appearing as uniformly illuminated disks, and revolving about their common center of gravity in circular orbits, mutually eclipse one another. It is required to find the relative dimensions and brightness of the two stars, and the inclination of the orbit, from the observed light.curve.
Page 10 - ... which we are in search of and yet may never obtain from its brighter rivals, the minuteness of an object is no reason for neglecting its examination But if small double stars are to be watched, it is first necessary that they should be known ; nor need we fear that the list will become overwhelming.