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Whirlpool Galaxy: image taken with our own telescope! the size of the field of view
- f our
Galaxies are everywhere...dim little points/smudges of light - - PowerPoint PPT Presentation
Galaxies are everywhere...dim little points/smudges of light - - PowerPoint PPT Presentation
Galaxies are everywhere...dim little points/smudges of light Whirlpool Galaxy: image taken with our own telescope! the size of the field of view of our telescope is 26 arc minutes Galaxies are everywhere...dim little points/smudges of light
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Galaxies are everywhere...dim little points/smudges of light This is an especially dark, uninteresting small part of the sky (2.5 arc minutes across)
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Virgo cluster: nearest big galaxy cluster
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Virgo cluster: nearest big galaxy cluster
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Galaxies are everywhere...dim little points/smudges of light and we can detect supernova explosions in them, even when they
- nly cover a
few pixels!
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2df galaxy survey: each dot is a galaxy
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there is a limit to the size scale of structure (~100 million light years)
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Large scale structure simulation
zoom in
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but first, The Cosmological Principle
weak: the Universe is the same everywhere (homogeneous and isotropic
- n large scales)
strong: also, the same at all times
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but first, The Cosmological Principle
weak: the Universe is the same everywhere (homogeneous and isotropic
- n large scales)
strong: also, the same at all times
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Contents of the Universe changes with time: Quasars as a function of redshift (and thus distance and lookback-time)
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but first, The Cosmological Principle
weak: the Universe is the same everywhere (homogeneous and isotropic
- n large scales)
strong: also, the same at all times strong: ruled out by observations; including the darkness of the night sky
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Olber’s paradox: if the Universe (or forest) were infinitely large, we’d see a star/galaxy (or tree) in every direction
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Cosmological Principle: Universe is the same everywhere homogeneous? scale is the key
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Chuck Close, Maggie, 1996 Jackson Pollock, Number 1, 1950 (Lavender Mist)
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a wheat field is homogeneous...but that characterization depends on the scale
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and it might be homogeneous without being isotropic
view from the left vs. the right?
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we observe isotropy on large scales; if we are not in a special place, then this implies global homogeneity
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On small scales, the Universe is clearly not homogeneous Working our way out from Earth in increasingly larger scales, here are some examples of inhomogeneity
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Earth and Moon: sizes to scale
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Earth and Moon: sizes to scale and distance to scale
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The Sun, our star: 8 light minutes away and 4 light seconds across
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The Sun, our star: volume about a million times larger than the Earth
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the distribution of stars in the sky is not uniform
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we live inside a flattened disk of stars: the Milky Way Galaxy
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Milky Way composite, seen from Earth’s surface
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Our neighbor galaxy: Andromeda
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Andromeda: thought to be much like the Milky Way corresponds to our location in the Milky Way
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Our neighbor galaxy: Andromeda infrared view
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The Whirlpool Galaxy (M51): grand-design spiral
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characterization of individual stars in galaxies: starting around 1915
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Virgo cluster: nearest big galaxy cluster
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Virgo cluster: nearest big galaxy cluster
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Edwin Hubble (late 1920s)
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Part of what made it possible to determine that Andromeda is a separate galaxy was the discovery of Cepheid variable stars by Henrietta Leavitt
she also developed a clever method for using these variable stars as distance indicators
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Hubble’s original (1929) velocity-distance relationship
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