Introduction to
Astrophysics and Cosmology
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GALAXIES
From current observations, it would appear that the large-scale structure of the cosmos ranges from stars – galaxies – clusters – superclusters, separated by voids. Before 1989, the common idea held was that superclusters were the largest structures in existence. However, in 1989, the “Great Wall” – a sheet of galaxies over 500 million light years long and twenty million wide – was discovered.
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Photometry
Astronomers can use spectroscopy and photometry to study stellar light in hopes of learning more about the universe we live in. A telescope with a spectrograph measures the spectrum of a star and gives the brightness at different wavelengths.
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A telescope equipped with a set of colored filters measures the intensity of a star’s image through different filters, allowing study of the distribution of different star’s radiation over the wavelength’s scale.
Large samples of stars are more efficiently studied using stellar photometry.
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