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Topic: Angular diameter distance

Related Topics

angular momentum

angular frequency

angular velocity

Angular resolution

angular acceleration

Proof of angular momentum

angular size

conservation of angular momentum

perturbed angular correlation

angular aperture

Angular diameter distance

orbital angular momentum

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	Angular diameter distance - Wikipedia, the free encyclopedia
		The angular diameter distance is a distance measure used in astronomy.
		The angular diameter distance depends on the assumed cosmology of the universe.
		The angular diameter distance to an object at redshift, z, is expressed in terms of the comoving distance, χ as:
	en.wikipedia.org /wiki/Angular_diameter_distance (120 words)

	Comoving distance - Wikipedia, the free encyclopedia
		The comoving distance is defined as the proper distance divided by a time-varying scale factor representing the expansion of the universe.
		However, while conformal time is identical to locally measured time for an observer at a fixed comoving spatial position, the comoving distance is not, in the general case, identical to a distance as physically experienced by a particle moving slower than or at the speed of light.
		The ordinary distance as experienced by particles travelling slower than or at the speed of light is simply the comoving distance multiplied by the value of the scale factor at the cosmological time studied.
	en.wikipedia.org /wiki/Comoving_distance (1124 words)

	Angular_Diameter
		The angular size (or angular diameter) of an object is simply the angle between one side of the object and the other.
		To determine the angular size of an object, we will take advantage of the fact that two round or spherical objects can have the same angular diameter, even if they are at very different distances from the observer.
		Using the angular diameter you calculated in step 6, and the known distance to the Moon, calculate the liner diameter of the Moon as you did in Part II of this lab.
	lpc1.clpccd.cc.ca.us /lpc/bazan/astro30/Angular_Diameter.htm (1591 words)

	Distance Measures in Cosmology
		The unifying aspect is that all distance measures somehow measure the separation between events on radial null trajectories, ie, trajectories of photons which terminate at the observer.
		For small v / c, or small distance d, in the expanding Universe, the velocity is linearly proportional to the distance (and all the distance measures, eg, angular diameter distance, luminosity distance, etc, converge)
		Angular diameter distance is related to the transverse comoving distance by
	www.astro.ufl.edu /~guzman/ast7939/projects/project01.html (1088 words)

	Angular measure (Site not responding. Last check: 2007-10-23)
		Small angles are readily related to the sizes and distances of the objects: the ratio of the size to the distance is the angular size measured in radians.
		If you imagine a circle centered on your eye and passing through the object, the distance to the object is the radius of the circle, and the arc of that circle occupied by the object has the same length as the width of the object.
		The ratio of arc length (the size of the object) to the radius of the circle (the distance to the object) is the angular size of the object in radians.
	mintaka.sdsu.edu /GF/explain/atmos_refr/angles.html (583 words)

	Angular Size (Site not responding. Last check: 2007-10-23)
		We can take the concept of angular distance between two objects one step further and speak of the angular size (or angular diameter) of an object -- the angular distance from one side of an object to the other.
		The angular diameter of an object depends on two things: the object's actual size, and the distance of the object from us.
		The units of actual diameter and distance are unimportant, as long as they are the same, i.e., both in km, both in miles, etc.
	www.austincc.edu /jheath/Solar/Hand/Angsize/angsiz.htm (235 words)

	The Distance Scale of the Universe
		Angular Diameter Distance is a good indication (especially in a flat universe like ours) of how near the galaxy was to us when it emitted the light that we now see.
		The Comoving Distance is the distance scale that expands with the universe.
		Comoving Distance is the opposite of the Angular Diameter Distance - it tells us where galaxies are now rather than where they were when they emitted the light that we now see.
	www.atlasoftheuniverse.com /redshift.html (807 words)

	IMSA Astrophysics: Distance Ladder
		The diameter of the moon and its distance from the earth represent the second part of the ground floor measurement.
		To determine the diameter of the moon, Aristarchus reasoned that he could measure the duration of time between the moment when the edge of the moon first entered the umbra and the moment when the moon was first totally obscured.
		The diameter of the earth, later determined by Eratosthenes, is 12,742 km.
	staff.imsa.edu /science/astro/astrometry/ground2.html (900 words)

	x-billion light years? (Site not responding. Last check: 2007-10-23)
		Of the three, the proper distance is perhaps the most sensible of the three.
		In this case, distance doesn't mean either when the light was emitted or received, but how far the light travelled.
		Turning this into an absolute distance (i.e., some number of light-years) requires us to plug in a rate for the expansion (the Hubble constant) and its change with time (the deceleration parameter), neither of which is as precisely known.
	homepage.ntlworld.com /brian.kilby/astro/1999/oct/x-billion-lightyears.html (448 words)

	Galaxies and the Universe - Extragalactic Distance Scale
		The procedure usually follows a distance ladder, in which objects of well-known properties are used to calibrate larger/brighter kinds of objects which can in turn be used to calibrate other indicators that may be seen to greater distances, until finally we have indicators that are useful into the realm of allegedly pure cosmological motion.
		Measuring the average radial velocity then allows a distance determination, as the distance for which the radial velocity and proper motion are consistent with the angle between line-of-sight and space motion.
		Their usefulness as a distance indicator relies on the fact that their luminosity function appears to be invariant, and is easily understood from stellar evolution (Jacoby 1989 ApJ 339, 39).
	www.astr.ua.edu /keel/galaxies/distance.html (4237 words)

	This Week in Computational Astrophysics » Recent Techniques and Applications (Site not responding. Last check: 2007-10-23)
		Angular diameter distance from the Sunyaev-Zel'dovich effect in galaxy clusters: calibration from hydrodynamical simulations
		The angular-diameter distance D_A of a galaxy cluster can be measuread by combining its X-ray emission with the cosmic microwave background fluctution due to the Sunyaev-Zeldovich effect.
		The application of this distance indicator usually assumes that the cluster is spherically symmetric, the gas is distributed according to the isothermal beta-model, and the X-ray temperature is an unbiased measure of the electron temperature.
	www.cita.utoronto.ca /~ljdursi/thisweekcomp/entry_193.php (429 words)

	Active Galaxies Educator Unit
		The relationship between angular diameter, distance, and appearance is shown below: the closer an object is, the larger the angle it covers and the larger it appears; the farther away an object is, the smaller the angle it covers and the smaller it appears.
		In astronomy, the angular diameter is usually measured directly and the equation is used to calculate the distance or the physical diameter of the object.
		To calculate the diameter of the emission region from the duration of the brightness variation we multiply the velocity of light (called c which equals 3x 10^8 m/s), by the length of time (called t or “delta t” or Δt) it takes the AG to change brightness.
	glast.sonoma.edu /teachers/agn/index.html (7886 words)

	THE SN1987A CIRCUMSTELLAR RING AND THE DISTANCE TO THE LARGE MAGELLANIC CLOUD
		That is all angular size is, a way to describe how large something appears to be in self-consistent units.
		It turns out that for things with a small angular size, their distance equals the actual size of the object divided by it's angular size.
		You are given the angular size of the piece of sky of the picture of the ring and you have to estimate the angular size of the ring itself which is smaller than that of the whole picture.
	super.colorado.edu /~astr1020/homework4/angular_size.html (698 words)

	angular diameter
		The angle that the actual diameter of an object makes in the sky; also known as angular size or apparent diameter.
		The Moon, with an actual diameter of 3,476 km, has an angular diameter of 29 '21" to 33' 30", depending on its distance from Earth.
		If both angular diameter and distance are known, linear diameter can be easily calculated.
	www.daviddarling.info /encyclopedia/A/angular_diameter.html (132 words)

	Cosmology and Cosmic Structure Evolution (Site not responding. Last check: 2007-10-23)
		The distance at the "cosmic now" is the radial co-moving coordinate distance (equal to the proper distance in a flat geometry), and appears in the Hubble Relation.
		The "distance then" is sometimes called the emission distance, and is a measure of how far away the galaxy was then when the light we see now left the galaxy.
		This emission distance can in principle be measured by comparing the angular sizes of a class of objects of similar physical size, and so is often called the angular diameter distance.
	homepages.wmich.edu /~korista/cosmology.html (868 words)

	Eber
		That distance is just the physical size of the spots on the recombination surface and it is used as a ruler against which other measurements are based.
		WMAP measured the angular size of the spots on the recombination surface, and compared this to the known physical size of the spots, our ruler, and deduced the distance to the recombination surface.
		There is actually another way to calculate the distance to the recombination surface (known as the angular diameter distance), using the expansion rate of the universe: the Hubble constant.
	www.its.caltech.edu /~sciwrite/journal03/eber.html (2879 words)

	The ABC's of Distances
		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.
		The diameter of the largest H II region in external galaxies has been taken as a "standard rod" that can be used to determine distances.
		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 (3918 words)

	Chandra :: Photo Album :: Scales and Angular Measurement
		The Sun and the moon have angular diameters of about half a degree, as would a 4-inch diameter orange at a distance of 38 feet.
		The angular diameter is proportional to the actual diameter divided by its distance.
		For example if an object is observed to have an apparent diameter of 1 arc second and is known to be at a distance of 5000 light years, it can be determined that the actual diameter is.02 light years.
	chandra.harvard.edu /photo/scale.html (351 words)

	2.4 Distance measures (Site not responding. Last check: 2007-10-23)
		In this section we summarize various distance measures that are defined in an arbitrary spacetime.
		lies in the fact that they relate cross-sectional diameters at the source to angular diameters at the observer, and this is always true, even beyond caustic points.
		This reflects the fact that the angular diameter of an image on the observer’s sky is subject to aberration whereas the cross-sectional diameter of an infinitesimally thin bundle has an invariant meaning (recall Section 2.3
	www.univie.ac.at /EMIS/journals/LRG/Articles/lrr-2004-9/articlesu4.html (1937 words)

	H.05 When people speak of galaxies X billion light years away, does this mean they are that far away now or were that
		There are at least three kinds of distances: * angular-diameter distance---the one you need to make the usual relation sine(angular size) = linear size/distance work; * luminosity distance---makes the typical relationship observed flux = luminosity / 4 pi (distance*2) work; and proper distance---the piece-by-piece distance the light actually travelled.
		Turning this into an absolute distance (i.e., some number of light-years) requires us to plug in a rate for the expansion (the Hubble constant) and its change with time (the deceleration parameter), neither of which is as precisely known as we might like.
		For the press release we quoted a distance of 2.4/3.4 x 15 billion light-years (rounded to 11 since that 15 is fuzzy).
	www.faqs.org /faqs/astronomy/faq/part8/section-14.html (589 words)

	2.3 Surveying the universe
		Robertson-Walker spacetimes have preferred foliations, so it is possible to define sensible notions of the distance between comoving objects - those whose worldlines are normal to the preferred slices.
		the observed angular velocity; and the angular-diameter distance,
		Note that, for large redshifts, the dependence of the various distance measures on z is not necessarily monotonic.
	relativity.livingreviews.org /Articles/lrr-2001-1/node8.html (349 words)

	High-Redshift Elliptical Galaxies in HDF
		Distances to these galaxies are generally not available and are difficult to estimate from their recession velocity alone because they are so nearby.
		For NGC 1023 and NGC 4649 I have used the distances measured by Ciardullo, Jacoby, and Tonry (1991) using planetary nebulae and for NGC 4486 (M87) the surface brightness fluctuation distance found by Tonry et al.
		It may be argued that the distances of the galaxies in the sample are uncertain, compromising the accuracy of the luminosities and the predicted HDF magnitudes.
	ecf.hq.eso.org /~ralbrech/sepdec97apjl/975277.html (4108 words)

	Homework 10 (Site not responding. Last check: 2007-10-23)
		However, everyone must submit their own solutions to get credit, and all help should be acknowledged (a single sentence mentioning the others in your study group is sufficient).
		Assuming the galaxies are located at a distance of 86 Mpc from us, calculate the mass of the parent galaxy.
		(c) [6 pts] Plot the angular diameter vs distance (in Mpc) for a galaxy with a linear diameter of 30 kpc.
	astrowww.astro.indiana.edu /~classweb/a222s0488/hw10.html (455 words)

	From theory to observables (Site not responding. Last check: 2007-10-23)
		is called the luminosity distance, L the intrinsic luminosity of the source and F is the measured flux.
		is the angular diameter distance, D is the proper size of the object,
		In a Robertson Walker Universe the proper motion distance reduces to the physical distance along a spacelike slice.
	khwarizmi.phy.iitb.ac.in /~yajnik/seminarhtml/node21.html (225 words)

	Approximate angular diameter distance in a locally inhomogeneous universe with nonzero cosmological constant (Site not responding. Last check: 2007-10-23)
		Approximate angular diameter distance in a locally inhomogeneous universe with nonzero cosmological constant
		We discuss the general and approximate angular diameter distance in the Friedman-Robertson-Walker cosmological models with nonzero cosmological constant.
		We modify the equation for the angular diameter distance by taking into account the fact that locally the distribution of matter is non homogeneous.
	www.edpsciences.org /articles/aa/abs/2003/45/aa4018/aa4018.html (168 words)

	Homework 8 (Site not responding. Last check: 2007-10-23)
		expanding at 150 km/s at a distance of 200 pc from the galactic center.
		(a) [5 pts] Plot the angular diameter vs distance (in Mpc) for a galaxy with a linear diameter of 30 kpc.
		The recession velocities of the satellite and the parent galaxy are measured to be 6450 km/s and 6500 km/s, respectively, and the two galaxies are separated by an angle of 30' on the sky.
	www.astro.indiana.edu /~classweb/a202s0497/homework8.html (529 words)

	:: NASA Quest > Archives :: (Site not responding. Last check: 2007-10-23)
		With reference to the orbit of a planet, the distance between the center of its orbit and the center of the primary about which it revolves.
		The squares of the periods of revolution of any two planets are proportional to the cubes of their mean distances from the sun.
		a celestial coordinate; it is the angular distance measured from the vernal equinox eastward along the celestial equator to the
	quest.arc.nasa.gov /mars/background/glossary.html (1360 words)

	Observations with Lensing
		Because the angular-diameter distance depends strongly on the cosmological model used, the lensing probability is a function of the cosmological constant, as shown below.
		This plot is for the case of a flat universe.
		If instead the galaxy number count is assumed to be fixed, the dependence of the lensing probability on the cosmological constant is much less.
	astro.berkeley.edu /~julie/observations.html (452 words)

	String-Dominated Universe Cosmology
		This altered angular diameter distance affects number count predictions, the probability of gravitational lensing, and the predictions for microwave background fluctuations.
		Thus, there are no cosmological constant models compatible with this observation, measurements of large-scale structure, measurements of the Hubble constant, and the constraint that the age of the universe exceed 11 Gyr.
		At the redshifts probed by the supernova study, the distance redshift relation in a string-dominated universe is close to, but not identical to, an open universe.
	ecf.hq.eso.org /~ralbrech/novdec97apjl/975744.html (3229 words)

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