DSST Astronomy notes 1

76 proper motion of a star is the rate at which its

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76) Proper Motion of a star is the rate at which its direction in the sky changes, is usually expressed in seconds of arc per year a) Almost always an angle that is too small to measure precisely in a single year a.i) Barnard’s Star – the star of largest known proper motion (a.i.1) Which changes its direction by 10.25 arc seconds per year 77) Luminous Flux – measures of the amount of light energy received from stars a) Most fundamental observational data of astronomy 78) Magnitude – the measure of light flux received from a star or other luminous object a) Six levels of classifications were set up from 1-6 magnitude (1 being the brightest stars) 79) Photometry – the branch of observational astronomy which deals with the measurement of the intensity of starlight a) Sir William Herschel – devised simple method of stellar photometry, based on light gathering power of a telescope in proportion to area of its lens b) More modern and accurate method of stellar photometry employs the visual photometer b.i)A device attached to telescope – an artificial star image 80) Star Color – apparent brightness of a star depends upon its color, the distance and the temperature of the star a) Eye is most sensitive to green and yellow light b) Less sensitive to the blue and violet light (shorter wavelengths) c) Longer wavelengths – orange and red light c.i) Photographic plates use color – sensitive photographic plates to filter the light to determine magnitude of brightness 81) Black Body – a perfect radiator is an idealized body that absorbs all the electromagnetic energy upon it a) Star heats up until it reaches a temperature at which it emits radiation at exactly the same rate as received, and remains in equilibrium temperature b) A perfect radiator at any temperature emits some radiation at all wavelengths, but not in equal amounts b.i)A hotter black body emits more radiation at all wavelengths that does a cooler black body b.ii) Hot stars appear blue because most of their energy is at short wavelengths b.iii) Cool starts appear red because most of their energy is at long wavelengths 82) Binary Star – is a double star or two stars revolving around each other
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a) Star Mizar – first double star discovered - in the middle of the handle of the Big Dipper b) Discovered by John Baptist Riccioli in 1650 83) Optical Binary Stars – consist of two stars in nearly the same line of sight a) Not true binary stars, but appear to be because of the line of sight b) Relatively rare 84) Massive Stars – are more luminous a) The relations is known as mass-luminosity relation b) 90% of all stars obey mass-luminosity relation 85) High Intrinsic Luminosity – the rate of radiation of electro-magnetic energy into space by a star, or its luminosity, determines how bright it looks a) Many stars that seem bright are hundreds of light years away and are brighter than the sun 86) Gauging – to view the distribution of stars in the sky a) William Herschel – observed that some directions he could count more stars than others b) Published results of gauges of stars in 1785 87) Milky Way– a luminous band of light that encircles the sky
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76 Proper Motion of a star is the rate at which its...

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