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Topic: Astronomical interferometers

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	Interferometry Summary
		This technique is the basis for astronomical interferometer arrays, which spread out over a wide area and can together produce a picture which is resolution similar or equivalent to a single telescope with the diameter of the combined spread of telescopes.
		The VLT Interferometer is expected to produce its first images using aperture synthesis soon, followed by other interferometers such as the CHARA array and the Magdalena Ridge Observatory Interferometer which may consist of up to 10 optical telescopes.
		However, interferometers are perhaps even more widely used in integrated optical circuits, in the form of a Mach-Zehnder interferometer, in which light interferes between two branches of a waveguide that are (typically) externally modulated to vary their relative phase.
	www.bookrags.com /Interferometry (5971 words)

	interference. The Columbia Encyclopedia, Sixth Edition. 2001-05
		The Michelson interferometer used in the Michelson-Morley experiment of 1887 to determine the velocity of light had a half-silvered mirror to split an incident beam of light into two parts at right angles to one another.
		The radio interferometer consists of two or more radio telescopes separated by fairly large distances (necessary because radio waves are much longer than light waves) and is used to pinpoint and study various celestial sources of radiation in the radio range.
		Astronomical interferometers consisting of two or more optical telescopes are used to enhance visible images of distant celestial objects.
	www.bartleby.com /65/in/interfrnc.html (852 words)

	Interferometry - Wikipedia, the free encyclopedia
		The interferometer setup shown to the right was used in the famous Michelson-Morley experiment that provided evidence for special relativity.
		Fabry-Pérot interferometers are widely used in telecommunications, lasers and spectroscopy for controlling and measuring the wavelength of light.
		This technique is the basis for astronomical interferometer arrays, which can make measurements of very small astronomical objects if the telescopes are spread out over a wide area.
	en.wikipedia.org /wiki/Interferometer (2569 words)

	Interferometers
		Interferometers cannot compete with the "Time Honoured" method of a knife edge and the human eye in a Double Pass Null test for accuracy.
		For astronomical mirrors where the accuracy required is a small fraction of a wavelength, they become highly dependant on the equipment quality and the skill of the operator.
		Interferometers results suggesting large smooth bumps in the centre of mirrors are much more likely to be errors in the Interferometer set-up or use.
	www.oldham-optical.co.uk /Interferometer.htm (4886 words)

	The Future of Astronomical Research
		Astronomical interferometers form an image in much the same way that a holograph is used to record the 3-dimensional image of an object on a piece of photographic film.
		An optical interferometer consisting of two Hubble telescopes separated by 1400 kilometers would just be able to resolve this distant star patch with an resolution of 0.0000001 arcseconds.
		Potentially, the most serious limitation to any of these "photon-counting" interferometers is the large number of photons entering the telescopes caused by naturally occurring sources of light unrelated to the object you are trying to study.
	www.astronomycafe.net /anthol/remote.html (2898 words)

	Online Encyclopedia and Dictionary - Very Large Telescope
		VLT is located at the Paranal Observatory on Cerro Paranal, a 2,635 m high mountain in the Atacama desert in northern Chile.
		The principle role of the VLT is to operate as four independent telescopes, and the interferometry (combining light from multiple telescopes) is a minor secondary role.
		The VLT is intended to achieve an effective angular resolution of 0.001 arcsecond at a wavelength of 1 µm, comparable to that achieved using other arrays such as the Navy Prototype Optical Interferometer and the CHARA Array.
	www.fact-archive.com /encyclopedia/VLT (634 words)

	NAIC-NRAO Single Dish Summer School
		While, in general, interferometers provide high spatial resolution for imaging small-scale structure (corresponding to high spatial frequencies in the Fourier plane), single-dishes can be used to image the largest spatial scales (corresponding to the lowest spatial frequencies), including the total power (corresponding to zero spatial frequency).
		Astronomers share the radio spectrum with a multitude of other users who transmit useful signals with a wide variety of spectral and temporal characteristics.
		I'll also gaze into the crystal ball and, to end, poll the astronomers present on what is their opinion of the subject.
	www.naic.edu /~astro/School/abstracts.shtml (2431 words)

	Astrobiology Magazine ::
		The effect on the appearance of an astronomical source due to the bending of light by the gravitational field of an intervening object.
		Astronomical interferometers work by combining the light of two or more telescopes to achieve the resolving power equivalent to a much larger telescope.
		Interferometers are widely used in radio astronomy, but the technique is more difficult to apply in the optical because of the disturbing effects of the earth's atmosphere.
	astrobio.net /news/Glossary.html (2311 words)

	SCI.CRYONICS: BONZO 2: Two photons interferometers.
		The intensity interferometer is a "particle-property" interferometer, that is, it does not matter what is the wavelength used to get information.
		The astronomical part of the project is there to develop, and finance the electronics and computer parts.
		Intensity interferometers was first used at the end of World War two, but forty years later they remain uncommon systems, largely ignored from many, including optical specialists.
	www.cryonet.org /cgi-bin/dsp.cgi?msg=4455 (537 words)

	SPIE Proceedings Vol. 3350
		Abstract: Since modern astronomical interferometers require a large number of sensors and actuators for closed-loop control of opto-mechanical components, reconfigurability of the hardware is a strongly desired feature of interferometer control software.
		The stellar interferometers require picometer accuracy 1D metrology gauges, surface metrology gauges and 3D metrology gauges to measure the required distances or to calibrate the fiducials that define the end points of the interferometric paths.
		Both the rotation rate of the interferometer about the normal to the plane containing the three spacecraft and the orientation in the plane must be determined accurately in order to permit the detection of white light fringes from sources that have visual magnitudes as high as possible.
	www.spie.org /web/abstracts/3300/3350.html (13424 words)

	Astronomical interferometer - Wikipedia, the free encyclopedia
		An astronomical interferometer or hypertelescope is an array of telescopes or mirror segments acting together to probe structures with higher resolution.
		Astronomical interferometers are widely used for optical astronomy, infrared astronomy, submillimetre astronomy and radio astronomy.
		One simple layout of astronomical interferometer is a parabolic arrangement of mirrors, giving a partially complete reflecting telescope (with a "sparse" or "dilute" aperture).
	en.wikipedia.org /wiki/Astronomical_interferometer (1319 words)

	Board on Physics and Astronomy and Astrophysics
		The survey committee obtained advisory studies from over 300 astronomers who participated in one or more of the 15 panels established to represent different wavelength disciplines, as well as solar, planetary, theoretical, and laboratory astrophysics.
		Astronomers use computers to collect and study billions of bytes of data every 24 hours and to make theoretical simulations of complex phenomena.
		For example, studies of the sun, the planets, and the stars have led to experimental techniques for the investigation of the earth's environment and to a broader perspective from which to consider terrestrial environmental concerns such as ozone depletion and the greenhouse effect.
	www7.nationalacademies.org /bpa/Bahcall_Survey_Contents.html (2089 words)

	Astrophysics Research at MIT
		MIT optical astronomers are also mapping lensing galaxies, which will remove some of the uncertainties currently associated with the theoretical modeling of gravitational lenses.
		The interferometers are operated in coincidence, so as to reject the noise from local environmental perturbations.
		Eventually, the LIGO may form a network with European and Asian interferometers to measure the polarization of the waves and determine source location with sufficient precision to allow identification by electromagnetic astronomies (radio, optical, x-ray, and g-ray).
	web.mit.edu /astrophysics/research.html (2874 words)

	[No title]
		He later moved on to use astronomical interferometers in the measurement of stellar diameters and in measuring the separations of binary stars.
		His interferometer made it possible for him to determine the width of heavenly objects by matching the light rays from the two sides and noting the interference fringes that resulted.
		In 1920, using a 6-metre interferometer attached to a 254-centimetre Hooker Telescope at Mt. Wilson near Pasadena, he succeeded in measuring the diameter of the star Betelgeuse (Alpha Orionis) as 386,160,000 km (300 times the diameter of the Sun).
	www.angelfire.com /scifi2/rsolecki/albert_michelson.html (1102 words)

	Interferometry (Site not responding. Last check: 2007-10-10)
		This technique is the basis for radio telescope arrays which, spread out over a wide area of hundreds of miles, can together produce a picture with resolution similar or equivalent to a single telescope with the diameter of the combined spread of telescopes.
		The VLT Interferometer is expected to produce its first images soon, followed by other interferometers such as the Keck Interferometer and the Magdalena Ridge Observatory Interferometer which may consist of up to 10 optical telescopes.
		An interferometer works on the principle that two waves that coincide with the same phase will amplify each other while two waves that have opposite phases will cancel each other out.
	interferometry.iqnaut.net (664 words)

	History and Development of the Telescope
		Galileo Galilei is generally credited with being the first to use a telescope for astronomical purposes in 1609, calling it at first a perspicillum, and then using the terms telescopium in Latin and telescopio in Italian (from which the English word derives).
		The preferred solution for small astronomical telescopes is to tip the altazimuth mount so that the azimuth axis is parallel with the axis of the Earth's rotation; this is known as an
		These allow many astronomical targets to be monitored continuously, and for large areas of sky to be surveyed.
	www.edinformatics.com /inventions_inventors/telescope.htm (1208 words)

	AN1: Millimeter-Wave Interferometers
		The local oscillator (LO) for the receiver is derived from the same source as the transmitter either by splitting the power from a common oscillator, or by phase-locking another oscillator to the transmitter source.
		The most critical component in the MMW interferometer is the receiver capable of producing two output signals, the in-phase and quadrature phase (I-Q channels) using a pair of balanced mixers and hybrid power dividers with accurate phase relationship.
		In addition, radio astronomical measurements often utilize a large receiver array in an interferometric configuration.
	www.quinstar.com /an01_millimeter_wave_interferometers.html (412 words)

	Astronomical interferometry,from the visible to sub-mm waves
		Since the delay line position is continually measured with an internal laser interferometer, we know D and thus the angle between the baseline vector and the direction to the star; this is a basic astrometric datum.
		Radio astronomers realized in the 1950’s that they can take advantage of Equation (1) and build imaging interferometers much more easily than their colleagues working in the visible wavelength region.
		There are now a number of mm-wave interferometers that perform imaging of continuum and line emission of objects as varied as nearby star-forming regions and distant galaxies in the young universe, with a spatial resolution of about 1 arc second.
	www.europhysicsnews.com /full/12/article13/article13.html (2194 words)

	Downing College : Stafford Withington (Site not responding. Last check: 2007-10-10)
		My work is concerned with the development of techniques for observing astronomical sources at wavelengths of between 1mm and 100 microns, or equivalently between the radio and far-infrared.
		This part of the electromagnetic spectrum, sometimes known as the THz region, is rich in information about the formation of stars in our own galaxy, the formation of galaxies in the very early Universe, and the nature of the exotic physical processes that were at work in the Big Bang itself.
		Withington, E.S. Campbell, and M.P. Hobson, A numerical procedure for simulating the behavior of multimode, bolometric, astronomical interferometers, J. Applied Physics, 97, 124909 (2005).
	www.dow.cam.ac.uk /dow_server/mfs/fellows/S._Withington.html (425 words)

	Scanning Tomographical Imaging Telescope
		For the past four centuries optical imaging devices in general and astronomical instruments in particular have relied on the circular aperture as the primary light-gathering element.
		The eminent optical engineers Daniel Schroeder, author of Astronomical Optics 2000, and Raymond Wilson, author of Telescope Optic 1999, are familiar with the optical arrangement of the STII and they have indicated that the rectangular aperture would be well suited to the construction of telescopes with resolving powers far beyond those presently envisioned.
		There are of course risks involved in undertaking a preliminary analysis of an astronomical instrument that constitutes a decided break with Galileo and Newton and consequently lacks the evolutionary foundation established by these pioneers whose basic design of the astronomical telescope has withstood the test of four centuries.
	www.pages.drexel.edu /~garfinkm/Scope.html (6589 words)

	Millimetre-wave interferometers (Site not responding. Last check: 2007-10-10)
		ATCA is also important as it is currently the only interferometer operating in the southern hemisphere giving it a unique role in astronomy.
		The France-based IRAM consortium operates a 5-element interferometer on the Plateau de Bure.
		Astronomical interferometry was first carried out at optical wavelengths in the early 20th Century using the `Michelson Stellar Interferometer' which allowed stellar diameters to be measured and binary stars to be resolved.
	www.astro.umd.edu /~agg/interferometers.html (941 words)

	Water Line Monitoring at OVRO: Introduction (Site not responding. Last check: 2007-10-10)
		While standard astronomical calibration techniques can remove slow, large scale atmospheric-induced phase drifts that occur over several minutes, these techniques are not able to remove the small scale fluctuations that occur on time scales of seconds.
		As current and future interferometers expand to longer baselines, it is becoming increasingly important to correct data for these rapid fluctuations in order to routinely achieve the anticipated sub-arcsecond resolution images.
		The Owens Valley Radio Observatory (OVRO) millimeter-wave interferometer is investigating one method to correct for rapid phase fluctuations by monitoring the 22.2 GHz atmospheric water vapor line along the line of sight of each telescope.
	www.astro.caltech.edu /~jmc/wlm/intro.html (188 words)

	DSN Science with the SKA
		A number of optical and IR interferometers are being built and/or are planned to be operational on time scale comparable to that of SKA.
		Radio interferometer arrays such as the VLA and MERLIN have sufficient sensitivity to image a small number of stellar wind systems with brightness temperatures ~10^4 K at a resolution of ~50 mas.
		However interfering sources tend to be in the near field of individual interferometers, and will have a different response to different members of a redundant set of interferometers, whereas astronomical sources will be in the far field, and will have identical responses to all members of the set.
	www.ras.ucalgary.ca /SKA/meeting_stuff/abstracts.html (4053 words)

	NASA Observatorium Observation of the Week (Site not responding. Last check: 2007-10-10)
		Arrays of astronomical telescopes, such as the VLA, are called interferometers.
		The greater the separation of the individual telescopes, the sharper the interferometer's view of distant objects.
		The newest addition to astronomical radio interferometers is the Japanese "Highly Advanced Laboratory for Communications and Astronomy" (HALCA), which is a twenty-six-foot diameter Earth-orbiting radio telescope linked with ground-based radio telescopes around the world to form the largest radio interferometer built to date.
	observe.arc.nasa.gov /nasa/ootw/1997/ootw_970507/ob970507.html (1005 words)

	ADASS 2003 Conference Proceedings
		SIM has two so-called guide interferometers to provide stable inertial orientation knowledge of the baseline, and a science interferometer to measure target fringes.
		The key to interferometer measurements is the white light fringe determination.
		SIM is a fringe-scanning interferometer that needs to acquire and track the white light fringe in order to equalize the paths of the two arms of the interferometer at the nanometer level.
	www.adass.org /adass/proceedings/adass03/P10-6 (1177 words)

	POINTS Abstracts (Site not responding. Last check: 2007-10-10)
		POINTS, an astrometric Optical interferometer with a nominal measurement accuracy of 5 microarcseconds for the angle between a pair of stars separated by about 90 deg, is presently under consideration by two divisions of NASA-OSSA.
		POINTS, an astrometric optical interferometer with a nominal measurement accuracy of 5 microarcseconds for the angle between a pair of stars separated by about 90 deg, is presently under consideration.
		Each interferometer detects a dispersed fringe (channeled spectrum), which falls on a CCD detector array nominally 8k elements long and a small number of elements wide.
	cfa-www.harvard.edu /~reasen/POINTS-abstracts.html (2554 words)

	Astronomical Times
		Several important time scales still follow the rotation of the earth, most notably civil and sidereal time, but of these are now derived from atomic time through a combination of earth rotation theory and actual measurements of the earth's rotation and orientation.
		Chapter 2 of the most recent Explanatory Supplement to the Astronomical Almanac [ref 1] gives an extensive summary of time standards and a list of original literature references.
		Polar motion is equivalent to a change in latitude and longitude of points on the earth's surface with respect to the earth's instantaneous rotation axis.
	www.cv.nrao.edu /~rfisher/Ephemerides/times.html (2060 words)

	Diphy - Digital Philately - View Stamp (Site not responding. Last check: 2007-10-10)
		The Hooker telescope was equipped in 1919 with a special attachment, an optical astronomical interferometer developed by Albert Michelson, much larger than the one he had used to measure Jupiter's satellites.
		The Infrared Spatial Interferometer (ISI) is an array of three 65 inch (1.65 m) telescopes operating in the mid-infrared.
		These and other astronomical interferometers are included in the List of astronomical interferometers at visible and infrared wavelengths.
	www.diphy.com /stamp/US2000.129 (1292 words)

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