Sun/Stars/Clusters Flashcards
Measures of the amounts of light energy, or _____________ ________, received from stars are among the most important and fundamental observational data of astronomy.
Luminous Flux. They are used in estimating both the distances and the actual output of energy of stars.
The measure of the amount of light flux received from a star or other luminous object is called ______________.
Magnitude. Six levels of classifications were set up from first through sixth magnitude, with the first denoting the brightest-appearing stars. This system of stellar magnitudes began in ancient Greece, but is still used today with the improvement of basing magnitudes on precise measurements of apparent or total luminosity rather than arbitrary and uncertain eye estimates of star brightness.
That branch of observational astronomy which deals with the measurement of the intensity of starlight is called _______________.
Photometry. Sir William Herschel devised a simple and direct method of stellar photometry. His method depended on the fact that the light-gathering power of a telescope is proportional to the area of its lens. A more modern and accurate method of stellar photometry employs the visual photometer, a device attached to a telescope which produces an artificial star image. Looking through the telescope, the astronomer can vary the brightness and color of the artificial star to match the real star and discern the amount of energy provided to the artificial star image to accomplish this match. This is a measure of the luminous flux of the real star.
The apparent brightness of a star can depend to some extent upon its ___________.
Color. Different colors produce different responses in the human eye. The eye is most sensitive to green and yellow light and has a lower sensitivity to the shorter wavelengths of blue and violet light and to the longer wavelengths of orange and red light. Photographic plates were devised to detect the light more accurately using color-sensitive photographic plates to filter the light to determine a more accurate magnitude of brightness.
The colors of stars are determined by the distance and the temperature of the star.
A perfect _____________ called a black body is an idealized body that completely absorbs all of the electromagnetic energy incident upon it.
Radiator. The star heats up until it reaches a temperature at which it emits radiation at exactly the same rate as it receives it, and then remains in equilibrium at that temperature.
The ___________ emitted from black bodies is relative to the different wavelengths at different temperatures.
Energy. A perfect radiator at any temperature emits some radiation at all wavelengths, but not in equal amounts. Note that a hotter black body emits more radiation at all wavelengths than does a cooler black body.
However, the big difference is that a hotter black body emits the largest proportion of its energy at shorter wavelengths than a cooler black body does. Hot stars appear blue because most of their energy is at short wavelengths and cool stars appear red because most of their energy is at long wavelengths.
A ____________ star is a double star or two stars revolving around each other.
Binary. In 1650, the Italian astronomer John Baptist Riccioli observed that the star Mizar, in the middle of the handle of the Big Dipper, appeared through his telescope as two stars. Mizar was the first double star to be discovered. In the century and a half that followed, many other closely separated pairs of stars were discovered telescopically.
_____________ binaries consist of two stars in nearly the same line of sight, of which one is far more distant than the other.
Optical. They are not true binary stars, but appear to be because of the line of sight. Optical binaries are relatively rare.
Optical. They are not true binary stars, but appear to be because of the line of sight. Optical binaries are relatively rare.
Massive. This relation is known as the mass-luminosity relation. This relation results from the fundamental laws that govern the internal structures of stars. About 90% of all stars obey the mass-luminosity relation (as you will learn later, the main sequence stars).
The most striking thing about the brightest-appearing stars is that they are bright not because they are nearby, but because they are actually of high intrinsic _________________.
Luminosity. The rate of radiation of electro-magnetic energy into space by a star, or its luminosity, determines how bright it looks. Many stars that seem so bright to the naked eye are hundreds of light years away and are actually brighter than the sun.
William Herschel, an English astronomer, sampled the distribution of stars about the sky by a procedure he called star ______________.
Gauging. He observed that in some directions he could count more stars through his telescope than in other directions. In 1785 he published the results of gauges of stars that he was able to observe in 683 selected regions scattered over the sky. In some areas, there was only a single star. In others, he counted over 600.
Visible to the human eye is a luminous band of light called the ___________ ________ that completely encircles the sky.
Milky Way. Galileo solved the first mystery of the Milky Way when his observations revealed that it really consists of myriads of faint stars. It is the light from many distant stars that appear lined up in projection when we look from our position on Earth.
The only parts of the sun that can be observed directly are its outer layers, collectively known as the sun’s ________________.
Atmosphere. The solar atmosphere does not consist of distinct layers with sharp boundaries. Rather, there are three general regions, each with different properties and each gradually transitioning into the next. The three regions are the photosphere, the chromosphere, and the corona.
The solar _______________ covers the range of depths from which the solar radiation escapes and is what we see when we look at the sun.
Photosphere. The light from the sun comes from the higher and cooler regions of the photosphere.
The region of the sun’s atmosphere that lies immediately above the photosphere is the ________________.
Chromosphere. The chromosphere was first observed during times of total solar eclipse. In 1868, the spectrum of the chromosphere was observed and found to be made up of bright lines, which showed that the chromosphere consists of gases that are absorbing light from the photospheric regions.
The chromosphere merges into the outermost part of the sun’s atmosphere, the ______________.
Corona. Like the chromosphere, the corona was first observed only during total eclipses, but unlike the chromosphere, the existence of the corona has been known for many centuries. Many of the early investigators regarded the corona as an optical illusion. The corona extends for at least a million miles beyond the photosphere and emits half as much light as the full moon.
