DSST Astronomy notes 1

87 milky way a luminous band of light that encircles

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87) Milky Way– a luminous band of light that encircles the sky a) Solved by Galileo – revealed that it consists of myriads of faint starts 88) Solar Atmosphere – the only parts of the sun that can be observed directly are its outer layers a) Three general regions a.i) Photosphere – covers the range of depths from which the solar radiation escapes – what we see when we look at the sun a.ii) Chromosphere – lies immediately above the photosphere (a.ii.1) Observed during times of totals solar eclipse (a.ii.2) In 1868 the spectrum chromosphere was found to be made up of bright lines and that it contained gases that are absorbing light from the photospheric regions a.iii) Corona – what the chromosphere merges into the outermost part of the suns atmosphere (a.iii.1) Also observed during total eclipse (a.iii.2) Unlike the chromosphere the corona has been known for centuries (a.iii.3) Often regarded as optical illusion (a.iii.4) Extends for at least a million miles beyond the photosphere and emits half as much light as the full moon 89) Sunspot – a temporary cooler region in the solar photosphere that appears dark by contrast against the hotter sun a) Galileo – first showed that sunspots are on the surface of the sun b) Regions where the gases are cooler than those surrounding the region 90) Spectroheliograph – was invented for photographing the sun or part of the sun in monochromatic light in 1892 a) Works with the Telescope to produce a photo of the sun’s surface based on selected wavelength of the spectrum isolated b) Wavelength is choses to correspond to the spectral wavelength of a specific element contained in the sun i.e.: hydrogen or calcium b.i)Sun is 99% hydrogen and helium b.ii) Also contains iron, silicon, and carbon 91) Plages – referred to as “clouds of calcium” or “clouds of hydrogen” and are seen through spectroheliograms a) Regions where calcium and hydrogen emit light at the wavelengths observed 92) Spicules – the small jet like spikes of gas rise vertically through the chromospheres and move upward with speeds near 20 km/sec and last for only a few minutes 93) Prominences – huge clouds of cool dense plasma suspended in the sun’s hot thin corona a) They appear as red flame-like protuberances rising above the limb of the sun b) Can be viewed at anytime
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94) Flares appear as intensely bright spots usually in the vicinity f a sunspot a) Usually reaches its maximum intensity within a few minutes and fades out 95) Proxima Centauri is the closest star from our son a) Which is 4.2 light years away 96) Variable Stars – stars that vary in light a) Are designated in order of time of discovery in the constellation in which they occur b) Once discovered they are named by a letter followed by the constellation where it appears 97) Variables of Star Brightness a) Estimating the magnitude of the variable by visual observation through a telescope b) Comparing the magnitude to the variable star to other stars c) Determining the magnitude of the star by photoelectric photometry d) The magnitude of a variable star changes with time and is called the “light curve” of that star
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87 Milky Way a luminous band of light that encircles the...

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