ASTR 1103 Lecture Notes - Lecture 15: Barred Spiral Galaxy, Sombrero Galaxy, Elliptical Galaxy
9 Feb 2020
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Document Summary
The andromeda galaxy: 1 trillion stars, 2. 5 million ly away, visible to the naked eye. In constellation virgo near spica: visible in amateur telescopes, clear dust band, 28 million ly away. Classification of galaxies: morphological according to shape, quantitative according to their luminosity and colour. Hubble"s morphological classification of galaxies: elliptical, spirals and barred spirals milky way is a barred spiral galaxy. Quantitative classification: blue cloud spiral and irregular, red sequence elliptical. Proportion of galaxies: 75% elliptic and spiral elliptic galaxies more common than spiral, 25% irregular, selection effect non-representative sample, spirals more visible than elliptical. Goods: great observations origins deep survey, survey of galaxies, uses space and ground telescopes, studied two areas in northern and southern skies. Distance ladder: the calibration used to build a distance scale extending from the size of earth to the most distant visible galaxies. Stellar parallax: used to measure distances to stars up to 1500 ly away.
