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Topic: Stellar parallax

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	Stellar Parallax (Site not responding. Last check: 2007-11-04)
		Stellar parallax the difference in direction of a celestial object as seen by an observer from two widely separated points.
		The measurement of parallax is used directly to find the distance of the body from the Earth (geocentric parallax) and from the Sun (heliocentric parallax).
		The largest measured stellar parallax is 0.76", for the nearest star, Alpha Centauri; the smallest that can be directly measured is about 25 times smaller, but indirect methods permit calculation of the parallax, inversely proportional to the distance, for more and more distant objects but also with more and more uncertainty.
	abyss.uoregon.edu /~js/glossary/parallax.html (161 words)

	parallax. The Columbia Encyclopedia, Sixth Edition. 2001-05
		Formally, the parallax of a star is the angle at the star that is subtended by the mean distance between the earth and the sun.
		A unit of stellar measurement is the parsec; it is the distance at which a star would have a parallax of one second of arc and is equivalent to 206,265 times the distance from the earth to the sun, or about 3.3 light-years.
		Geocentric parallax is a technique similar to stellar parallax, which uses the diameter of the earth rather than the diameter of its orbit as a baseline.
	www.bartleby.com /65/pa/parallax.html (461 words)

	Wikinfo \| Parallax
		Parallax is the change of angular position of two stationary points relative to each other as seen by an observer, due to the motion of said observer.
		The parsec is the distance for which the annual parallax is 1 arcsecond and hence the maximum parallactic shift is 2 arcsecond.
		Dynamic parallax has sometimes also been used to determine the distance to a supernova, when the optical wave front of the outburst was seen to propagate through the surrounding dust clouds at an apparent angular velocity, when we know its true propagation velocity to be that of light.
	www.wikinfo.org /wiki.php?title=Parallax (1335 words)

	parallax - HighBeam Encyclopedia
		Trigonometric parallax is the apparent displacement of a nearby star against the background of more distant stars resulting from the motion of the earth in its orbit around the sun.
		A unit of stellar measurement is the parsec ; it is the distance at which a star would have a parallax of one second of arc and is equivalent to 206,265 times the distance from the earth to the sun, or about 3.3 light-years.
		Spectroscopic parallax is the most widely used technique for determining the distances of stars that are too distant for their stellar parallaxes to be measured.
	www.encyclopedia.com /doc/1E1-parallax.html (577 words)

	Parallax - Search Results - MSN Encarta
		Parallax, also called parallactic shift, the apparent displacement of the position of a celestial object on the celestial sphere when viewed from...
		Parallax View, The, motion picture about an assassination conspiracy rooted in corporate America, based on the novel by Loren Singer.
		Stellar Parallax, apparent change in star position, used in determining stellar distances.
	ca.encarta.msn.com /Parallax.html (111 words)

	Early Methods of Measuring the Distance to Stars
		and the detection of annual parallax with instruments subject to shrinking and warping with the passage of the seasons was daunting task.
		Since Bradley was unsuccessful in determining annual parallax he was able to estimate from the accuracy of his measures that the stars must be at least 400 000 AU from the sun.
		It was not until 1838 that the first parallax was measured, and was done by three scientists independently using three different instruments to measure stellar parallax: Bessel with his heliometer, Srure with his filar micro meter and Henderson with his meridian circle.
	www.astro.utoronto.ca /~bclarke/AST199M/stellar_distances.htm (1851 words)

	Untitled Document
		With the acceptance of the idea of a moving Earth orbiting the Sun, it became possible to reconsider the notion that the stars are all at the same distance from the center of the Universe (the Sun in the Copernican model).
		Parallax is simply the change in the apparent position of a nearby object relative to a more-distant object due to a change in the position of the observer.
		If the Earth moves and parallax shifts are not observed from one side of its orbit to another, then either the stars are all exactly at the same distance from the Sun, or they are so far away that the shifts are too small to observe.
	www.nd.edu /~jkolata/phys171/Distances/Parallax.html (713 words)

	Lecture 21: Rotation & Revolution of the Earth
		The "non-observation of stellar parallaxes" was one of the principal objections to the Copernican heliocentric model.
		The first stellar parallax was observed in 1837 by the astronomer Friedrich Wilhelm Bessel for the star 61 Cygni.
		Parallaxes, the "final proof", were to be elusive for more than a century, and were one of the chief goals of astronomers in this period.
	www-astronomy.mps.ohio-state.edu /~pogge/Ast161/Unit4/movearth.html (1357 words)

	Hipparchus, Bessel and Stellar Parallax
		A star A in January is seen in position B and in July as a star situated in C. The average distance to the Sun, the astronomical unit A.U. is approximately 150 million kilometers.
		The parallax angle of the nearest star is less than 1/3600 of one degree, it is like trying to see a penny size object from a distance 4 km away.
		No stellar parallax could be measured showing as a sign of the Earth revolution around the Sun.
	www.mlahanas.de /Greeks/Astronomy2.htm (606 words)

	[No title]
		The method is known as stellar parallax which is the reflection of the annual motion of the Earth around the Sun as measured against the fixed background of stars.
		Every measurement of this star therefore produces the same value for the parallax and the errors in the window labelled error histogram are confined to one single bin.
		Error per measurement is comparable to the actual parallax These measurements have a large error per measurment so you will seldom see the star shift exactly on the reference points A and B as it does in the case of no error.
	zebu.uoregon.edu /disted/ph122/lec10.html (800 words)

	stellar_parallax
		Their measurement of the parallax of Mars could then be used to obtain the distance to Mars, and hence, deduce the size of the astronomical unit.
		Modern satellite surveys have measured parallax with extreme precision and have mapped the distances in the galaxy.
		Robert Hooke (1669) believed he had seen a stellar parallax in the motion of a star called gamma draconis of 15".
	www.calstatela.edu /faculty/kaniol/a360/stellar_parallax.htm (686 words)

	Parallax (Site not responding. Last check: 2007-11-04)
		Stellar distance estimates are crucial to understanding stellar properties and underpin the whole distance network for galactic and extragalactic astronomy.
		The greatest parallax occurs when the earth is at the ends of its orbit.
		Note how the parallax decreases as the star moves further away and increases as the star move closer to the earth.
	instruct1.cit.cornell.edu /courses/astro101/java/parallax/parallax.html (315 words)

	Curious About Astronomy: Is there a proof that Earth moves?
		Parallax should not be confused with aberration: parallax arises from the change of Earth's position and depends on the distance to the star, while aberration is caused by Earth's great speed and does not depend on how far the star is.
		This was a very important discovery because Aristotle himself mentioned the lack of observable stellar parallax as the proof that the Earth is not moving (he didn't have a telescope and didn't know that the stars are so distant).
		So, aberration (slight change in stellar positions due to Earth's speed), parallax (slight change in stellar positions due to Earth's changing position) and Doppler effect (slight change in color of stars due to Earth's speed) all prove that Earth is moving around the Sun, and not the other way round.
	curious.astro.cornell.edu /question.php?number=190 (705 words)

	Stellar Astronomy (Site not responding. Last check: 2007-11-04)
		Directly from parallax via the principles of trigonometry plus a knowledge of the size of the orbit of the earth
		Equivalently, stellar surface temperature can be used in place of spectral type.
		If luminosity is measured in terms of magnitude and temperature is indicated via a measure of stellar color, then we have a color-magnitude diagram - this is essentially the same as an HR diagram.
	www.missouri.edu /~physwww/astronomy_one/html/stellar_astronomy.html (679 words)

	Parallax (Site not responding. Last check: 2007-11-04)
		Generally speaking, parallax is the apparent shift in the direction to an object as seen from two different locations.
		Stellar parallax occurs as the Earth orbits the Sun and our line of sight to a nearby star varies.
		In reality, stellar distances are so great that parallax shifts are less than an arc second, completely unobservable to the unaided eye.
	astsun.astro.virginia.edu /~jh8h/glossary/parallax.htm (146 words)

	Bradley's Discovery of Stellar Aberration
		Unfortunately, the direction of the change was not what one would have expected, if it were caused by stellar parallax, and additional observations, of other stars, were attempted, to clarify the matter.
		(Parallax produces an elliptical motion, circular at the Ecliptic poles, and linear at the Ecliptic plane, whose semi-major axis equals the reciprocal of each star's distance in parsecs, which is of course different for different stars.
		Stellar aberration produces an elliptical motion, circular at the Ecliptic poles, and linear at the Ecliptic plane, whose semi-major axis equals a constant, regardless of the distance or angular position of the star, equal to one radian multiplied by the ratio of the Earth's orbital velocity, to the speed of light.
	cseligman.com /text/history/bradley.htm (1516 words)

	Comins & Kaufmann, Discovering the Universe (Site not responding. Last check: 2007-11-04)
		The parallax (p) of the star is equal to the angular radius of the Earth's orbit as seen from the star.
		The distance d to the star (in parsecs) is found by taking the reciprocal of the parallax angle p (in arcseconds): d = 1 / p.
		The closer the star is to us, as in the second part of the animation, the greater the parallax angle p.
	www.physics.uoguelph.ca /phyjlh/Astro/animations/StellarParallax.htm (88 words)

	Parallax
		That means that the angle α; between AC and BC is small; that angle is known as the parallax of C, as viewed from AB.
		All observed parallaxes are less than 1", at the limit of the resolving power of even large ground-based telescopes.
		In measuring star distances, astronomers frequently use the parsec, the distance to a star whose yearly parallax is 1"--one second of arc.
	www-istp.gsfc.nasa.gov /stargaze/Sparalax.htm (934 words)

	Outln Ch22
		Parallax angles are measured based on the apparent shift of the stars against the stellar background as the Earth orbits the sun.
		The parsec (parallax second) is the distance corresponding to a parallax of exactly one second, while a light-year is equal to the distance travelled through space by light in one year.
		STELLAR CLASSIFICATION: An early attempt to classify stars, the spectral classification, was based on the fact that light spectra are influenced by the kinds and relative abundances of elements present in the radiating body.
	www.tamuk.edu /Geo/Jordan/MAJCourses/Fall_1999/ES2/coch22.htm (2747 words)

	IMSA Astrophysics: Distance Ladder
		Stellar classification can be used as a very effective tool for determining stellar distances, when parallax has reached its limitations, around 0.390" or 26 parsecs.
		Although technological improvements will continue to increase this distance, really distant stars in the galaxy will need to have their distances determined by the indirect method of applied stellar classification, called spectroscopic parallax.
		Quite simply, stars whose distances are well known (through trigonometric parallax measurements) have been placed on a H-R diagram.
	staff.imsa.edu /science/astro/astrometry/stellarclass.html (298 words)

	parallax — FactMonster.com
		; it is the distance at which a star would have a parallax of one second of arc and is equivalent to 206,265 times the distance from the earth to the sun, or about 3.3 light-years.
		parallax - parallax -- Listen to the pronunciation: WAV format or AU format Uncle Mike finds parallax to be...
		parsec - parsec [parallax + second], in astronomy, basic unit of length for measuring interstellar and...
	www.factmonster.com /ce6/sci/A0837583.html (451 words)

	Parallax (Site not responding. Last check: 2007-11-04)
		The basic measurement for stellar distance data is parallax -- an apparent shift of nearby objects with respect to farther ones, as seen from a moving location.
		For stellar measurements, the moving object is the Earth, as it moves around the Sun every year.
		Galileo tried to measure the expected parallax of stars, to verify Copericus' heliocentric theory of the Universe, but his telescope was not powerful enough.
	www.astro.wesleyan.edu /~anna/Astro211/0219b.html (302 words)

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