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Unformatted text preview: Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson & McMillan, Astronomy Chapter 15 Normal and Active Galaxies Galaxies and the Universe Galaxies Prior to the Great Debate of 1920, it was Prior unclear if the universe consisted of unclear The disk-llike collection of stars around ike The the sun, now called “The Milky Way The Galaxy” Galaxy OR There were many galaxies distributed through space through Great Debate of 1920 Great The discovery of Galaxies The argument was whether the fuzzy The nebulae in the sky were: All llocal objects in our Galaxy (e.g. All ocal emission nebula, young star clusters) emission OR OR Sometimes huge collections of stars at Sometimes huge great distances great Charting the Galaxies Charting In 1921 Edwin Hubble showed that Andromeda (M31) was 700,000 parsecs away away This indicates that Andromeda must be a vast collection of stars comparable to our Galaxy our Hubble set about surveying galaxies to determine their properties determine A universe filled with galaxies This is the Hubble Deep Field – a tiny tiny patch of sky patch More galaxies than anything else anything Just a handful of stars in this image image Galaxies in The Hubble Deep Field The A very long, deep exposure with HST HST Range of galaxy colours and colours and shapes All elongated – not pointlike not pointlike Hubble Classification Scheme Hubble Hubble surveyed galaxies using the new 2.5 m (100 inch) Hooker telescope on Mt Wilson (built 1917) Mt In 1924, he set out a visual (by eye) classification scheme for all galaxies: classification Spirals, Barred Spirals, Ellipticals and Spirals, Ellipticals and Irregular galaxies Irregular Spiral Galaxies Spiral Spiral Galaxies are always Large Disk shaped Contain gas and dust in the disk Contain Are relatively blue due to young stars forming in the disk in The Bulge iis a rounded central region Bulge s containing older stars containing Regular Spiral Galaxies Regular Denoted by the letter S with a letter a-d Denoted indicating a combination of The size of the Bulge The How tight the spiral arms are How Sa, Sb, Sc, Sd Sa, Sb Sc, Sd Smaller Bulge Looser arms Sa Sb Sc M81 Face on Sa Problems of projection Problems dust Sombrero Sombrero Galaxy: Edge on Sa Edge Barred Spirals Barred Sometimes the spiral galaxy has a rectangular bar shape in the centre rectangular The arms stars from the end of the bar The Denoted: SBa, SBb, SBc SBa SBb SBc SB a d SB Smaller Smaller Bulge/Bar Bulge/Bar Looser Looser arms arms Barred Galaxies?...
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