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Topic: Cosmic distance ladder

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	Cosmic distance ladder - Wikipedia, the free encyclopedia
		The cosmic distance ladder refers to the methods by which astronomers determine the distances to celestial objects.
		At the base of the ladder are radar observations of Venus, which allow one to determine the distance between the Earth and Venus and by extension, the size of the orbit of the Earth.
		The field of astronomy which measures distances is known as astrometry.
	en.wikipedia.org /wiki/Cosmic_distance_ladder (181 words)

	cosmic distance ladder
		Distances within the Solar System are known to extreme accuracy by a variety methods, including the motions of the planets in the sky, radar, and timing of signals from interplanetary probes.
		Distances to stars within a couple of thousand light-years come from various geometrical methods; the most accurate values are those based on measurements of the annual parallax of about 10,000 nearby stars made by the Hipparcos satellite.
		Extragalactic distance indicators enable estimates to be made of the Hubble constant, a measure of the rate at which the universe as a whole is expanding.
	www.daviddarling.info /encyclopedia/C/cosmic_distance_ladder.html (486 words)

	Cosmic distance ladder
		I will measure distances in light years: one light year is the distance covered by light during one year, which is about 9.5 trillion kilometers, or about 6 trillion miles.
		A student is in her room sitting at her desk and would like to find the distance to the window; she gets a ruler and laboriously measures this distance to be 3 feet.
		Since we already knows the distance to the window (which she measured using her ruler) and she now knows the time it takes sound to go from her desk to the window and back she can determine the speed of sound.
	phyun5.ucr.edu /~wudka/Physics7/Notes_www/node109.html (429 words)

	Astronomical units of length - Wikipedia, the free encyclopedia
		The distances are closely related to the cosmic distance ladder.
		The distances to distant galaxies are typically not quoted in distance units at all, but rather in terms of redshift.
		The reasons for this are that converting redshift to distance requires knowledge of the Hubble constant which was not accurately measured until the early 21st century, and that at cosmological distances, the curvature of space-time allows one to come up with multiple definitions for distance.
	en.wikipedia.org /wiki/Astronomical_units_of_length (187 words)

	The ABC's of Distances
		Another method can be used to measure the average distance to a set of stars, chosen to be all about the same distance from the Earth.
		When distances to nearby stars were found using trigonometric parallaxes in the late 19th and early 20th century, it became possible to study the luminosities of stars.
		A figure [75 kB] to illustrate this shows a nearby dwarf galaxy, a nearby giant galaxy, and the giant galaxy at a distance such that its total flux is the same as that of the nearby dwarf.
	www.astro.ucla.edu /~wright/distance.htm (3899 words)

	Cosmic Distance Ladder (Site not responding. Last check: 2007-10-18)
		At very large distances such as those to galaxies further away than nearby clusters, astronomers can no longer use the methods such as trigonometric parallax or Cepheid variables that we have discussed before.
		At those distances, astronomers turn to a series of methods that often use standard candles: objects whose absolute magnitude is thought to be very well known.
		They can be used to measure distances out to around 1000-2000 Mpc, which is a significant fraction of the radius of the known Universe.
	csep10.phys.utk.edu /ojta/course2/galaxies/expanding/ladder_tl.html (533 words)

	Cepheid variable
		A yellow giant or supergiant pulsating variable whose period of pulsation is directly related to its luminosity: the longer the period, the greater the mean intrinsic brightness.
		This strict period-luminosity relationship makes Cepheids important cosmic distance indicators, since, by measuring a Cepheid’s period and comparing the intrinsic brightness, which this yields, with the apparent brightness, the star’s distance can be worked out.
		In addition, since Cepheids are so bright that they can be seen in other galaxies, they help establish a distance scale well beyond the Milky Way (see cosmic distance ladder).
	www.daviddarling.info /encyclopedia/C/Cepheid_variable.html (336 words)

	The Cosmic Distance Ladder, I: Parallax
		This article will be the first of a series on the Cosmic Distance Ladder, which calibrates the distance to everything outside our solar system.
		With these measurements we can calibrate angular measurements of the motions of the sun and planets to determine their distances, as well as the mass of the sun (via Newtonian gravity).
		Because an arcsecond is the fundamental unit for this work, a unit of distance, the parsec is used to reflect the physical distance at which an object produces as parallax of one arcsecond.
	www.suite101.com /article.cfm/astronomy/11999 (445 words)

	The Cosmic Distance Ladder, III: Measuring the Hubble Constant
		The Cosmic Distance Ladder, III: Measuring the Hubble Constant
		So important is measurement of the Hubble constant that many of the century's greatest astronomers have spent their entire careers working on the topic, and a principal justification for the Hubble Space Telescope was to measure it.
		Hence, if the constant of proportionality is known, the distance can be determined to any galaxy, provided is speed of recession.
	www.suite101.com /article.cfm/astronomy/13754 (541 words)

	Cosmic Ladder (Site not responding. Last check: 2007-10-18)
		The answer to this is somewhat obvious: Earth is at the right distance, as a function of sun's position (and thus temperature) in the HR diagram.
		The radius of the star will increase and although its temperature will drop, earth will be scorched to death because of the decreased distance between sun and earth.
		What matters is that there is this horrendous realization that the planets of the solar system have been a "ladder" of sorts.
	users.forthnet.gr /ath/jgal/writing/CosmicLadder.html (1229 words)

	Measuring Cosmic Distances With Stellar Heart Beats
		There is indeed no accurate, direct way to determine the distance to galaxies beyond the Milky Way: astronomers first determine the distance to nearby stars in our galaxy as accurately as possible and then use a series of other techniques that reach progressively further into space to estimate distances to more distant systems.
		The distances to four of the stars (Eta Aql, W Sgr, Beta Dor and L Car) were derived using the interferometric Baade-Wesselink method, as their pulsation is detected by the VLTI.
		Combining the distances measured by this programme with the apparent magnitudes of the stars, the astronomers determined the absolute magnitude (intrinsic brightness) of these stars and arrived at a very precise calibration of the zero-point of the Period-Luminosity relation (assuming the slope from previous work).
	www.spacedaily.com /news/astro-navigation-04f.html (1672 words)

	Step 1: distances up to 100 (Site not responding. Last check: 2007-10-18)
		For near-by stars their distance is measured by parallax: the star is observed in, say, December and then in June, and the direction of the star with respect to the sun is measured in both cases.
		Figure 8.5: Knowing the size of Earth's orbit and measuring the angles of the light from the star at two points in the orbit, the distance to the star can be derived.
		The farther the star is, the smaller the angles.
	phyun5.ucr.edu /~wudka/Physics7/Notes_www/node110.html (133 words)

	Chandra Press Room :: Chandra Shows New Way to Measure Cosmic Distances :: April 25, 2000 (Site not responding. Last check: 2007-10-18)
		By analyzing the time variations in the halo, the astronomers determined that the distance to Cygnus X-3 is 30,000 light years, within about 20 percent accuracy.
		The X-ray scattering method of measuring cosmic distances depends on the fact that X-rays, because of their high energies, are scattered through small angles by dust grains.
		If so, it would help astronomers in their quest to understand the size and age of the universe, since it would provide an independent estimate of the size of the first steps on the cosmic distance ladder.
	chandra.harvard.edu /press/00_releases/press_032000cygx399.html (785 words)

	Winter 2002 - The Winter Sky
		This is the series of steps which we go through in order to extend the astronomical distance scale to the edge of the universe.
		Trigonometric parallaxes, where we measure the change in the apparent position of a star as the earth moves around the Sun, are used to determine the distances to the closest stars, but even the Hyades is too distant for reliable results from this method when earthbound telescopes are used.
		In order to work, this method requires that the cluster be large enough that the convergent point be well defined and that the motion be large enough to give accurate measurements and that it be directed neither directly along nor perpendicular to the line of sight.
	www.mira.org /newsletr/nlwin01/5WinterSky.htm (930 words)

	The Cosmic Distance Ladder (Site not responding. Last check: 2007-10-18)
		Determining the distance to an object is one of the most difficult tasks in astrophysics.
		With the most accurate telescopes available, this technique can be used to measure the distances to stars out to a few hundred light years.
		It is these measurements that allow us to determine the distance scale across the billions of light years that separate us from the distant galaxies.
	www.rotse.net /summary/defs/distance.html (820 words)

	The Cosmic Distance Ladder (Site not responding. Last check: 2007-10-18)
		The exercises measure a succession of distance ratios, systematically stepping out in scale from the familiar world of everyday objects to larger and larger things, ultimately exploring the expansion rate of the universe as a whole.
		The second lab studies astronomical parallax, simulating the apparent motion of stars as the Earth goes around the sun in its orbit, a technique which first gave the distances to stars (in terms of the Earth-Sun distance) in the nineteenth century.
		The third lab constructs a Hubble diagram of galaxy distances and redshifts; coupled with the Cepheid distance calibration, this yields a measurement of Hubble's constant and an estimate of the expansion rate and age of the universe.
	www.astro.washington.edu /labs/Distance_Ladder.html (226 words)

	How do we measure the distances to things in space? (Site not responding. Last check: 2007-10-18)
		It is not an easy thing to measure the distances to objects in the Universe since these objects are usually very far away.
		To measure distances in the Universe, we will need to construct what is commonly referred to as a "cosmic distance ladder".
		In other words, astronomers use different methods to determine the distances to objects; the specific method which is used depends on how far away the object is. But all of the methods are wonderful combinations of science and mathematics!
	starchild.gsfc.nasa.gov /docs/StarChild/questions/question39.html (218 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		Except for the two Magellanic Clouds (visible from the southern hemisphere), which turn out to be small, satellite galaxies of the Milky Way, we did not know the distances to any other galaxies: they were so far away that we could not obtain spectra of the individual stars.
		Only the most luminous stars were visible, and these stars are difficult to use for distance estimates due to their large intrinsic spread in luminosity.
		To calibrate Type I supernovae, we used the other distance techniques (such as Cepheid varaibles) to estimate the distances to the nearest galaxies that had Type I supernovae explosions.
	ganymede.nmsu.edu /tharriso/ast110/class22.html (2741 words)

	Measuring Cosmic Distances with Stellar Heart Beats (ESO Press Release 25/04)
		For all purposes, these stars are all at the same distance (the size of the SMC is negligible compared to its much larger distance from us).
		By dividing the angular and linear measures, the distance to the star is obtained.
		The agreement between these two independent, geometrical calibrations is remarkable and greatly increases the confidence in the cosmic distance scale now in use.
	www.eso.org /outreach/press-rel/pr-2004/pr-25-04.html (1822 words)

	SETI Course blog: Week 2: The Distance Scale and the Drake Equation (Site not responding. Last check: 2007-10-18)
		Some of the material covered in Chapter 2 is also covered in a nice web page by Nick Strobel that has useful animations; I encourage you to read that, especially if you're at all confused by some of the material in the text.
		This week we talked a bit about the Distance Ladder, and the scales of distances in the Universe.
		There is a good web page at NASA on the cosmic distance ladder; well worth reading.
	flash.uchicago.edu /~ljdursi/SETI/blog/printer.php?id=1076283317 (244 words)

	Cosmic Distance Ladder (Site not responding. Last check: 2007-10-18)
		The use of standard candles to determine large distances in the Universe is a highly technical issue because there are many things that one has to correct for or assume before arriving at a final answer.
		It should not be too surprising to find that there are some legitimate disagreements on exactly how to do this.
		Such uncertainties are usually resolved by further observation, but they lead to quantitative uncertainty until then.
	csep10.phys.utk.edu /ojta/course2/galaxies/expanding/ladder_tr.html (92 words)

	Do Atoms Get Bigger as the Universe Expands?
		The metric encodes a lot of information; the part we care about (for this FAQ entry) is distances between objects.
		Page 719 discusses this very question; Box 29.4 outlines the "cosmic distance ladder" and the difficulty of measuring cosmic distances; Box 29.5 presents Hubble's work.
		Chapter 2 discusses the cosmic distance ladder; chapters 6 and 7 explain FRW spacetimes.
	math.ucr.edu /home/baez/physics/Relativity/GR/expanding_universe.html (1091 words)

	Type II Supernovae as distance indicators (Site not responding. Last check: 2007-10-18)
		The application of the ``expanding photosphere method'' (EPM) to Type II supernovae offers the possibility to determine extragalactic distances independently of the cosmic distance ladder.
		I perform a detailed assessment of the performance of EPM from a sample of 17 supernovae.
		Although these objects display a wide range in absolute luminosities, I show that the candles can be standarized to a level of 0.5 mag which proves similar to the precision yielded by EPM.
	www.lco.cl /ociw/seminars/abstracts/mhamuy.html (88 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		A copy of the presentation will be provided to the professor to check for accuracy and for distribution to the class (PowerPoint is encouraged but not required).
		In your presentation, make sure that you cover the basic technique, range of relevant distances, potential problems, and sources of error.
		Chapters 2 and 7 in Binney & Merrifield are good places to start, but also include “recent” results from at least one scientific journal paper.
	www.chara.gsu.edu /~crenshaw/Presentation.doc (91 words)

	ASTR100 (0202-0205)
		Match the following steps in the distance ladder (ways to determine distance to astronomical objects).
		___ uses objects we know the real luminosity (and distance) of nearby to figure out distances of similar objects that are farther away
		___ uses the appearance of a cluster’s main sequence stars to calibrate distance
	www.astro.umd.edu /~lwinter/Teaching/ASTR100.htm (180 words)

	General Education Course Syllabus
		Stellar evolution and nucleosynthesis, the universe beyond the solar system and the cosmic distance ladder, fl holes and other exotic objects, galaxies, origin and evolution of our universe.
		Describe the sun's motion around the center of the Galaxy and explain the techniques used to find the distance and speed of this motion.
		Describe methods used to find the distances to galaxies.
	www.runet.edu /~academic/colleges/cas/astr/syllabi/astr112.html (975 words)

	Elizabeth Wehner - Astro 103/104 Session 1 (Site not responding. Last check: 2007-10-18)
		We talked about the cosmic distance ladder and its importance to astronomy.
		During the early 1900's this important question of how large our universe truly could be, was answered.
		Here's what your classmates had to say about various rungs on the distance ladder:
	www.astro.wisc.edu /~wehner/honors/one.php (162 words)

	GALAXIES and the COSMIC DISTANCE LADDER (Site not responding. Last check: 2007-10-18)
		The COSMIC DISTANCE LADDER starts with distances to stars in our own galaxy:
		The TULLY-FISHER RELATION is an independent distance indicator
		When distances (r) were calibrated using Cepheid variables, Hubble found:
	www.chara.gsu.edu /~wiita/a1020lecture_23.html (945 words)

	Determining the Extragalactic Distance Scale (Site not responding. Last check: 2007-10-18)
		In this lab we will study a class of pulsating stars called Cepheid Variables.
		These stars play a key role in establishing the cosmic distance ladder and can be used to determine distances far greater than what cam be measured with trigonometric parallax alone.
		In this lab, we will search for Cepheids in another galaxy, M100, and then use the Cepheids to determine the distance to that galaxy.
	tesla.phys.unm.edu /a111labs/cepheids (86 words)

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