Distance Ladder
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The Transit of Venus and the understanding of Distances in the Universe
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Distance Ladder
- 1. Distance Ladder 2012-Apr-13 mississauga.rasc.ca
- 2. How far is it to the Moon, Planets Sun? How far to the nearest stars? How far to Galaxies? How big is the Universe? How old is the Universe? 2012-Apr-13 mississauga.rasc.ca
- 3. Moon, Nearest Milky Nearby Galaxy Planets, Stars Way Galaxies Clusters Sun Closer Farther 2012-Apr-13 mississauga.rasc.ca
- 4. Moon, Planets, Sun Nearest Stars Milky Way Nearby Galaxies Galaxy Clusters [RADAR] [Parallax] [Main Sequence [Cepheids] [White Dwarf Fitting] Supernovae] Trigonometry Luminosity-Temperature-Distance Tully-Fisher, et al. Redshifts 2012-Apr-13 mississauga.rasc.ca
- 5. Moon, Planet Nearest Stars Milky Way Nearby Galaxy s, Sun Galaxies Clusters [Parallax] [Main [RADAR] Sequence [Cepheids] [White Dwarf Fitting] Supernovae] Trigonometry Luminosity-Temperature-Distance Tully-Fisher, et al. Redshifts 2012-Apr-13 mississauga.rasc.ca
- 6. • Multiples of Feet! • Probably first derived guess Eratosthenes (200s BCE) • Calculated 40,000 stadia • Or 6,280 km – 8,360 km (based on different standard feet in the Ancient World) • Land/sea/air/space based trigonometric measurements mean radius of 6,371 km 2012-Apr-13 mississauga.rasc.ca
- 9. Moon, Nearest Stars Milky Way Nearby Galaxy Planets, Sun Galaxies Clusters [Parallax] [Main [RADAR] Sequence [Cepheids] [White Dwarf Fitting] Supernovae] Trigonometry Luminosity-Temperature-Distance Tully-Fisher, et al. Redshifts 2012-Apr-13 mississauga.rasc.ca
- 13. Moon, Nearest Milky Way Nearby Galaxy Planets, Sun Stars Galaxies Clusters [Main [RADAR] [Parallax] Sequence [Cepheids] [White Dwarf Fitting] Supernovae] Trigonometry Luminosity-Temperature-Distance Tully-Fisher, et al. Redshifts 2012-Apr-13 mississauga.rasc.ca
- 15. Moon, Nearest Milky Way Nearby Galaxy Planets, Sun Stars Galaxies Clusters [Main [RADAR] [Parallax] Sequence [Cepheids] [White Dwarf Fitting] Supernovae] Trigonometry Luminosity-Temperature-Distance Tully-Fisher, et al. Redshifts 2012-Apr-13 mississauga.rasc.ca
- 18. Moon, Pl Nearest Milky Nearby Galaxy anets, S Stars Way Galaxies Clusters un km Astronomical U Light Year Mega Parsec 2012-Apr-13 mississauga.rasc.ca
- 19. • AU Astronomical Unit is approximately the mean distance from the center of the Sun to the center of the Earth (~150,000,000 km) • ly Light-Year is the distance light travels in a vacuum in a Julian year (~10 trillion km) • pc A parsec is the distance from the Sun to a parallax-arc-second displaced object (3.26 ly or ~31 trillion km) • Mpc A Mega parsec is 3,261,000 ly 2012-Apr-13 mississauga.rasc.ca
- 20. • Voyager 1 is about 116 AU away • Proxima Centauri is about 4.2 ly away • the Pleiades are about 120 pc away • the Milky Way is about 30 kpc across • Andromeda Galaxy is 800 kpc away • the Virgo Cluster is about 16.5 Mpc • the boundary of the observable universe has a radius of about 14 Gpc 2012-Apr-13 mississauga.rasc.ca
- 21. • You need to get the AU right • Used to be only visual observation of the Venus Transit and very good mathematics could do it • Now there is RADAR of Venus and Mars, but that still requires very good “radio” observation and mathematics 2012-Apr-13 mississauga.rasc.ca
- 22. • A 0.0005% error in the angular measurement of the Transit of Venus means a 1% error in the AU and a 1% error in a parsec (or 2062.56 AU) • A 1% error in distance at the Cepheid stage represents a 2.3% error in the Luminosity difference • This carries through to the expansion number 2012-Apr-13 mississauga.rasc.ca
- 23. • Our measurements of the Transit of Venus are key to understanding the distance of the AU • This gives us a good value for a parsec • Which in turn helps us figure out luminosity and distance of stars in the Milky Way • Helping us to find where Cepheid are and how far away close Galaxies are • Which in turn helps us understand the expansion of the Universe! 2012-Apr-13 mississauga.rasc.ca
- 24. The Transit of Venus is Very Important 2012-Apr-13 mississauga.rasc.ca
Notes de l'éditeur
- For the time, the stadion was the current large unit of measure equal to 600 feet. A standing army was expected to march 100 stadia in a day (or about 11 miles). Alexander’s armies could march 13, while the cavalry could ride 40.
- From a 10th century manuscript