ASTRON 1F03 Lecture Notes - Lecture 6: Barred Spiral Galaxy, Gravitational Lens, Distant Star

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Most of the stars particularly at the center are blocked by interstellar dust. Variable stars are stars whose luminosity varies periodically. We can calculate they luminosity, their apparent brightness and using ab= l / 4 d2 we can nd the distance. 2 types of variables ll lyrae, periods from 0. 5 to 1 day and cepheid variables which are more singular. Infant for them, the longer the pulsation period the more luminous they are. If we know the period, we gure out the luminosity and its apparent brightness and we calculate distance. This happens due to internal instability of these stars. The center of our milky way was estimated by looking at these clusters: we assume that they are evenly distributed around the galactic bulge (reasonable assumption since the universe is homogenous) and we found the center of distribution. Galactic structure: the galactic halo and the globular clusters formed very early. The galactic disk is where the youngest stars lie.

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