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Topic: Angular size

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	Angular size -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-09)
		Angular size is a measurement of how large or small something is using rotational measurement ((additional info and facts about degrees of arc) degrees of arc, (additional info and facts about arc-minute) arc-minutes, and (additional info and facts about arc-second) arc-seconds).
		This is why angular size is useful in (The branch of physics that studies celestial bodies and the universe as a whole) astronomy - with minor exceptions, everyone is the same distance (give or take the tiniest fractions) from the objects being measured.
		While angular sizes measured in degrees are useful for larger patches of sky (in the constellation of Orion, for example, the three stars of the belt cover about 3 degrees of angular size), we need much finer units when talking about the angular size of galaxies, nebulae or other objects of the night sky.
	www.absoluteastronomy.com /encyclopedia/a/an/angular_size.htm (365 words)

	Encyclopedia: Angular size (Site not responding. Last check: 2007-10-09)
		Angular size is a measurement of how large or small something is using rotational measurement (degrees of arc, arc_minutes, and arc-seconds).
		It is easy to understand angular size by imagining that you standing some distance from some kind of large landmark, like the Golden Gate Bridge.
		This is why angular size is useful in astronomy - with minor exceptions, everyone is the same distance (give or take the tiniest fractions) from the objects being measured.
	www.nationmaster.com /encyclopedia/Angular-size (376 words)

	UFO Size Estimator (Site not responding. Last check: 2007-10-09)
		This method of estimation requires fairly accurate determinations of the angular size of a UFO, and its distance from the observer, compared to the apparent size of a known object such as the Moon.
		There are a few methods for determining the angular width of a UFO but the one used here is based on comparisons with the angular size of the moon and a constant value derived from the Moon's actual diameter (2160 miles) divided by the Moon's mean distance from the Earth (238856 miles).
		Angular Size The size that an object appears to be.
	terrygroff.com /ufotools/size (708 words)

	[No title]
		the angular size is equal to the arc divided by the radian.
		The angular size in radians of the person standing 54" from me with a width of 18" is easy to find.
		The angular size is the arc length (Lillan's hieght) over the radius (length across the room).
	www.mtholyoke.edu /~mpeterso/classes/math101/jitt10ans.html (1088 words)

	StudyWorks! Online : Understanding Angular Sizes (Site not responding. Last check: 2007-10-09)
		The size that something appears to an observer is called the “Angular Size” and is measured in degrees like an angle.
		The angular size of the Moon varies from 29' 23.0" to 33' 31.8" during the course of a month.
		The Sun's angular size varies from 31' 27.7" to 32' 31.9" during the course of a year.
	www.studyworksonline.com /cda/content/article/0,,EXP789_NAV2-78_SAR712,00.shtml (620 words)

	From the Cover: Explaining the moon illusion -- Kaufman and Kaufman 97 (1): 500 -- Proceedings of the National Academy ...
		to a reduction in the perceived size of the moon (11).
		The notion that perceived angular size of the moon determines its perceived distance is diametrically opposed to the apparent
		in angular size (0.6°), it was evident that the horizon moon was
	www.pnas.org /cgi/content/full/97/1/500 (4879 words)

	The Angular Size of the Moon and Other Planetary Satellites: An Argument For Design
		The angular sizes were calculated using the average distance (semi-major axis) of each orbit (epoch February 1, 1997).
		For instance, the ratio of the moon's apparent diameter to that of the sun is 0.9719.
		Furthermore the greatly diminished apparent size of the sun at the distances of the larger planets means that any total solar eclipse there would lack the visual effect as seen from the earth.
	www.creationresearch.org /crsq/articles/35/astrodesign.html (2865 words)

	Why do astronomers measure things in degrees instead of meters (Site not responding. Last check: 2007-10-09)
		However, since the astronomer doesn’t usually know the distances and sizes of the objects she views, she wouldn’t be able to figure out the angle the same way.
		Use this distance, and its angular size, to determine the diameter of the Moon.
		It’s interesting to note that the angular size of objects is universal for all observers on Earth – everyone measures the same angle, regardless of the size of the telescope’s field of view.
	web.haystack.mit.edu /pcr/documents/angleactivity.htm (1087 words)

	ASP: Biography of a Star: Our Sun's Birth, Life, and Death
		In principle, you could measure angular size with the same device normally used in the classroom to measure angles: a protractor.
		The factor 57.3 is a conversion factor that changes the angular size in units called radians to a value in degrees.
		Measure the angular size of the ruler from each position using the pinhole protractor and record this in the worksheet.
	www.astrosociety.org /education/publications/tnl/39/sun3.html (1409 words)

	Basic Geometry
		The object's angular size is determined by the ratio size/distance.
		The quarter's linear size (2.5 cm) is 1.4 times as big as the dime's (1.8 cm) and so must be placed 1.4 times farther away to subtend the same angle.
		Now move the quarter two times closer as in the lower drawing, and its angular size is twice as big (20 degrees instead of 10 degrees).
	boojum.as.arizona.edu /~jill/NS102_2004/geom.html (893 words)

	Telescope - Open Encyclopedia (Site not responding. Last check: 2007-10-09)
		Telescopes increase the apparent angular size of objects, as well as their apparent brightness.
		Radio telescopes are often operated in pairs, or larger groups to synthesize large "virtual" apertures that are similar in size to the separation between the telescopes: see aperture synthesis.
		The Very Large Telescope (VLT) is currently (2002) the record holder in size, with four telescopes each 8 meters in diameter.
	open-encyclopedia.com /Telescope (1190 words)

	More About Angular Size
		An object's angular size is the angle between the lines of sight to its two opposite sides.
		An object's angular size is a measure of how large the object actually appears to be (which is a function of both actual size and distance away).
		In astronomy, the angular sizes of most objects are much smaller than even a single degree.
	imagine.gsfc.nasa.gov /YBA/HTCas-size/more-ang_size.html (291 words)

	Astronomy 101 Specials: Aristarchus and the Size of the Moon
		His genius was to use something he knew about the Earth (its size) and a bit of clever geometry to deduce the size of the Earth's shadow at the distance of the Moon.
		Aristarchus realized that the longest lunar eclipses must occur when the Moon passes right through the center of the Earth's shadow, and furthermore, that the angular size of the Earth's shadow could be measured by noting the difference in the position of the Moon before and after the eclipse.
		In addition, since the Moon and the Earth's shadow at the distance to the Moon are by definition at the same distance, the ratio of angular sizes is the ratio of physical sizes.
	www.eg.bucknell.edu /physics/astronomy/astr101/specials/aristarchus.html (738 words)

	Angular measure (Site not responding. Last check: 2007-10-09)
		The apparent sizes of distant objects and things in the sky are measured by the angle they subtend at the eye.
		The angular diameter of the Sun or the Moon is only about 1/4 of that, or just over 1/2 degree, which is 30 minutes of arc.
		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.
	mintaka.sdsu.edu /GF/explain/atmos_refr/angles.html (507 words)

	Astronomy 10: Parallax (Site not responding. Last check: 2007-10-09)
		angular size) of the marks to be 1°.
		The diameter (i.e., size) of the Moon is 3,476 km.
		The "size" will be the distance between your eyes, and the "angular size" will be the angle between two distant landmarks.
	cse.ssl.berkeley.edu /bmendez/ay10/2002/projects/parallax.html (1140 words)

	The Moon Illusion
		The moon's angular size is nearly constant as it moves across the sky, the moon subtending about 0.5 degree in the sky.
		Another real physical effect causes the angular size of the moon's image on the retina to be about 2% smaller when the moon is near the horizon, compared to its size near the zenith.
		When an object of constant size is seen near the horizon at A, and then near the zenith at B, we judge that both are "on" the apparent sky bowl, and therefore the object seems to be at A' and B', with A' being farther away than B', and is therefore judged to be larger.
	www.lhup.edu /~dsimanek/3d/moonillu.htm (8816 words)

	Plasma Laser Stars 1976 Paper
		The envelope function in the largest angular size-redshift diagram for quasars is shown to be a consequence of the distribution of their redshifts and to have no intrinsic physical significance.
		Curves obtained for the angular size from two world models, namely those of Einstein-de Sitter, and de Sitter, for a source of a fixed linear size of 290 kpc were found to provide reasonable upper envelopes to the plotted points.
		The indication was that the angular size falls off with redshift faster than one might expect for values of the deceleration parameter, q0, as determined from the apparent magnitude-redshift diagram for galaxies.
	laserstars.org /V1976a (1376 words)

	Moon Illusion Explained!
		Because the moon's angular size remains constant, photographs of the horizon moon and zenith moon taken with the same camera settings yield images which are the same size, as represented by Figure 1.
		Moreover, this basic angular size illusion necessarily is accompanied either by a distance illusion or by a linear size illusion or else all three illusions occur together.
		As the moon rises, its angular size appears to remain constant, and the basic illusion is that it appears to come closer as it approaches the zenith, so the horizon moon will look farther away than the zenith moon, hence look a larger linear size.
	facstaff.uww.edu /mccreadd/intro9.htm (5590 words)

	Princeton Montage
		The high resolution version will be printed out at a size of 46 inches wide by 61 inches high and displayed in their entrance foyer, next to another large mural (at the same angular size) of data from the Sloan Digital Sky Survey.
		As its name implies, angular size is an angle measured in degrees (remember that there are 360 degrees in a circle).
		So, an arc second (a common angular size in astronomy) is 1/3600th of a degree, and less than a millionth of a circle (1/1,296,000).
	terpsichore.stsci.edu /~summers/viz/princeton_montage (401 words)

	[No title]
		Since the ratio of finger size to arm size is approximately the same for different persons, most people have a fingerwidth of ~2° no matter what the length of their arms.
		When you start to measure angular sizes, you will soon realize that there is a relation between the angular size of an object and the distance to that object.
		The cross staff is a simple device (used for centuries before ~ AD 1600) for measuring the angular separation between two objects, or the angular size of a single object and (sometimes) thereby deriving its linear size or distance.
	www.astro.washington.edu /labs/clearinghouse/labs/Skywatch/angles.html (951 words)

	EDUCATION.JPL.NASA.GOV - JPL Education Gateway
		Ask what happened to the size of the sighting object and the measure of the angle when the students moved back from 3 meters to 5 meters.
		Answer: Size of the sighting object and angular size both decreased because when you view an object from farther away it appears smaller, therefore its angular size is smaller.
		Allow each student pair to measure the angular size of the object with their quadrant.
	education.jpl.nasa.gov /educators/angular.html (491 words)

	NIFS CoDR - Optical Parameters (Site not responding. Last check: 2007-10-09)
		Given also that the width of the slitlets is matched to two pixels, and that the anamorphic factor of the grating is dictated by other considerations, the angular area of the field is fixed.
		The angular size of the field in the spatial direction is given by
		mrad, and the focal length at the field mirror array is 128 m, the angular fanning pitch of the IFU is 0.2537°, the total fanning angle is 7.1036°, the circumferential pitch of the pupil mirror array elements is 1.984 mm, and the circumferential pitch of the field
	msowww.anu.edu.au /~peter/nifs/codr/codr_optical_parameters.htm (1079 words)

	Debunking the Moon Hoax
		The angular size of an object is the object's size divided by its distance, as long as the distance is much larger than the size.
		Si, in this case, the angular size is 13 billionths of a radian (the metric unit of angular measure).
		To convert from radians to degrees, multiply the angular size in radians by 180 and divide by pi (3.1415....).
	www.ucolick.org /~robin/moonhoax.html (566 words)

	The structure of southern extragalactic radio sources.
		The angular size is to be understood according to the size flag as follows: d Separation of peaks in a double source.
		In this case, the size is the distance between components which may be matched by examination of the source names.
		Pairs of sources were also sometimes given angular sizes for both the separation of centroids and the separation of peaks in a double.
	www.cs.wisc.edu /niagara/data/nasa/ApJS_80_137.xml (1639 words)

	How Big is a Star? (Site not responding. Last check: 2007-10-09)
		The radius of very few stars can be computed from their angular size (as seen from Earth) and their distance from Earth.
		Most stars are so far away from the Sun that their angular size is not resolved, even in large telescopes.
		If the angular size `a' of a star and the distance `d' to that star are known, then the radius `R' of the star can be computed.
	www.stormpages.com /swadhwa/stellarevolution/lecture5.htm (541 words)

	Box 1 - Nature Neuroscience (Site not responding. Last check: 2007-10-09)
		(a) The looming stimulus subtends an angular size
		In the locust's brain, the spiking activity of LGMD is relayed to neurons that are involved in the generation of flight steering and jump escape behaviors.
		An attractive possibility would be for the excitatory, motion-dependent input to be encoded in logarithmic coordinates and for the inhibitory input to be linear in angular size.
	www.nature.com /neuro/journal/v3/n11s/box/nn1100_1171_BX1.html (457 words)

	The distribution of angular sizes (Site not responding. Last check: 2007-10-09)
		The angular size of a source was defined as the mean of the major and minor axis of the fitted elliptical Gaussian.
		They are probably smaller than indicated on the plots and would continue the trend of decrease in angular size observed by Richards, 2000.
		calculates the total flux from the deconvolved angular size and the peak flux, figure 2.11 illustrates the surface brightness limit of source at low signal to noise.
	www.astro.soton.ac.uk /~ns/thesis/node41.html (224 words)

	Rob's Lesson Plan 4 for the Galactic Plane Surveys (Site not responding. Last check: 2007-10-09)
		By measuring the angular size of a source, you will be able to calculate its distance from the earth.
		The angular size is also used in a correction factor to calculate the temperature of a source in the next exercise.
		The result is the angular size of NGC 7027 in arcseconds.
	www.gb.nrao.edu /~glangsto/lessons/lessonDISTANCE.html (436 words)

	Moon Illusion Explained: Section 2
		And to have a perceived linear size of 10 units it must be at a distance from point O equal to 2/3rds the distance of 'horizon moon'-15.
		This "size" is, of course, the perceived linear size.
		Indeed, this linear size constancy must occur in order for the increase in the perceived visual angle to yield the shorter perceived distance as an example of the relative angular size cue to distance.
	facstaff.uww.edu /mccreadd/sectionII.html (3794 words)

	Chandra :: Photo Album :: Scales and Angular Measurement
		The apparent sizes of and distances between objects are described with angular measurement.
		It is also 400 times more distant, so it appears to be the same size as the full moon; that is, it has the same angular size.
		The angular diameter is proportional to the actual diameter divided by its distance.
	chandra.harvard.edu /photo/scale.html (343 words)

	Re: Real and Apparent Size? (Site not responding. Last check: 2007-10-09)
		Angular size can be expressed in degrees, but of more direct use is the angular size in radians.
		For an object the angular sized of the moon or sun, approximately 1/2 degree or about 0.009 radians (9 milliradians), at a distance of 1 km, the actual size (perpendicular to the lie of sight) would be about 0.009 x 1000 = 9 meters.
		Note that this calculation only gives the size as "projected" onto a line that is perpendicular to the line of sight.
	www.virtuallystrange.net /ufo/updates/1998/sep/m21-026.shtml (476 words)

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