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Topic: Astronomical units of length

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  Length - Wikipedia, the free encyclopedia
Length is a measure of one dimension, whereas area is a measure of two dimensions (length squared) and volume is a measure of three dimensions (length cubed).
Units of length may be based on lengths of human body parts, the distance travelled in a number of paces, the distance between landmarks or places on the Earth, or arbitrarily on the length of some fixed object.
Units used to denote distances in the vastness of space, as in astronomy, are much longer than those typically used on Earth and include the astronomical unit, the light-year, and the parsec.
en.wikipedia.org /wiki/Length   (332 words)

 Astronomical units of length - Wikipedia, the free encyclopedia
Astronomers use a number of different length units for different objects.
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   (180 words)

 astronomy - Hutchinson encyclopedia article about astronomy
The reform of European astronomy began in the 15th century by astronomers and mathematicians seeking to clarify and correct astronomical texts (especially Ptolemy's); however it was not until the following century, with the discoveries of Copernicus, that the Sun was proved to be the centre of the planetary system.
Also significant was the first measurement of the distance of a star, when in 1838 the German astronomer Friedrich Bessel measured the parallax of the star 61 Cygni, and calculated that it lies at a distance of about 6 light years (about half the modern value).
Astronomical spectroscopy was developed, first by Fraunhofer in Germany and then by people such as Pietro Angelo Secchi and William Huggins, while Gustav Kirchhoff successfully interpreted the spectra of the Sun and stars.
encyclopedia.farlex.com /astronomy   (1499 words)

 Astronomical unit - Facts, Information, and Encyclopedia Reference article
For greater precision, the International Astronomical Union in 1976 defined the AU as the distance from the Sun at which a particle of negligible mass, in an unperturbed circular orbit, would have an orbital period of 365.256 898 3 days (a Gaussian year).
While the value of the astronomical unit is now known to great precision, the value of the mass of the Sun is not, because of uncertainty in the value of the gravitational constant.
A conversion to SI units would separate the results from the gravitational constant, at the cost of introducing additional uncertainty by assigning a specific value to that unknown constant.
www.startsurfing.com /encyclopedia/a/s/t/Astronomical_unit.html   (839 words)

 Encyclopedia :: encyclopedia : Foot (unit of length)   (Site not responding. Last check: 2007-10-29)
A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a metre.
The most commonly used foot today is the English foot, used in the United Kingdom and the United States and elsewhere, which is defined to be exactly 0.3048 metre.
The imperial foot was adapted from an Egyptian measure by the Greeks, with a subsequent larger foot being adopted by the Romans.
www.hallencyclopedia.com /Foot_(unit_of_length)   (394 words)

 Light Year Encyclopedia Article @ LaunchBase.net (Launch Base)   (Site not responding. Last check: 2007-10-29)
The actual, exact length of the light-year depends on the length of the reference year used in the calculation, and there is no wide consensus on the reference to be used.
In astronomy, the preferred unit of measurement for such distances is the parsec which is defined as the distance at which an object will generate one arcsecond of parallax when the observing object moved one astronomical unit perpendicular to the line of sight to the observer.
Units related to the light year are the light-minute and light-second, the distance light travels in a vacuum in one minute and one second, respectively
www.launchbase.net /encyclopedia/Light_year   (409 words)

 A Dictionary of Measures, Units and Conversions
The units may be found either by looking under the category in which they are used [such as length, mass, density, energy etc.], or else by picking one unit from an alpabetically ordered list of units.
The unit of length was the metre which was defined as being one ten-millionth part of a quarter of the earth's circumference.
The SI unit of length is the metre.
www.bioinfo.rpi.edu /~zukerm/dictunit.html   (4915 words)

 IAU Website: Units
The symbol for the astronomical unit of length is au; the astronomical unit of time is 1 day (d) of 86 400 SI seconds (s); the astronomical unit of mass is equal to the mass of the Sun and is often denoted by Mo, but the special subscript makes this symbol inconvenient for general use.
An appropriate unit of length for studies of structure of the Galaxy is the parsec (pc), which is defined in terms of the astronomical unit of length (au).
The unit known as the light-year is appropriate to popular expositions on astronomy and is sometimes used in scientific papers as an indicator of distance.
www.iau.org /Units.234.0.html   (1578 words)

 astronomical unit   (Site not responding. Last check: 2007-10-29)
A unit of distance, roughly equal to the average distance from the earth to the sun, about 149,600,000,000 meters.
The astronomical unit of time is the day, defined as 86,400 seconds (the second as defined in SI), and the astronomical unit of mass is the mass of the sun, by definition 1.
that 1) dimensions of celestial bodies, velocities, etc. be described in kilometers, 2) "la distance moyenne du soleil à la terre, ou unité astronomique" [the average distance between the sun and earth, or astronomical unit] be used for distances in the solar system and 3) the parsec be used for distances to stars.
www.sizes.com /units/astronomical_unit.htm   (346 words)

 Units of Length
He asserts as a general principle that all “natural” units of length fluctuate, and the proof of it would be the comparison of the English foot (304.797 mm.) with the Paris foot (324.839), the Lyons foot (341.760) and the Bordeaux foot (356.740).
In reconstructing the overall structure of the units of length I have shown that the longest foot is the foot of 18 basic fingers which is the edge of the cube containing a basic talents of barley, and that to this foot corresponds a barley cubit of 27 basic fingers.
The length of ancient stadia had been intensely studied in the period between Newton and the French Revolution, when the exact measurement of the circumference of the earth was a lively problem; by the end of the eighteenth century all the ancient texts then available had been explained.
www.metrum.org /measures/length_u.htm   (16305 words)

 Units of Length
In reconstructing the overall structure of the units of length I have shown that the longest foot is the foot of 18 basic fingers which is the edge of the cube containing a basic talent of barley, and that to this foot there corresponds a barley cubit of 27 basic fingers.
This unit of 120 cubits, often called aslu, “cord,” in the texts, is the sexagesimal multiple of the double cubit, which in turn is composed of 60 fingers.
The length of ancient stadia has been intensely studied in the period between Newton and the French Revolution, when the exact measurement of the circumference of the earth was a lively problem; by the end of the eighteenth century all the ancient texts then available had been explained.
www.brandonlodge.org /gauge.htm   (16611 words)

 The MSDS HyperGlossary: Distance Unit Conversions
An astronomical unit is defined as the mean distance between the Earth and the Sun.
A unit of distance that would be traversed in a period of one year by an object moving at the speed of light in a vacuum (300,000,000 meters per second).
A unit of distance equal to the distance from the sun to a point having a heliocentric (sun-centered) parallax of one second (second as an angle, not a time unit).
www.ilpi.com /msds/ref/distanceunits.html   (805 words)

The achievable accuracy is largely affected by the baseline length or distance between individual antennas on the ground, the path of the vehicle during propulsion, the unpredictable features of the propagation path between the radar system antenna and the vehicle, and, of course, equipment errors.
All of the dimensions used by the astronomer in the solar system are known to very great precision in terms of the astronomical unit as a reference base; for example, the distance from Earth to Mars at a given instant can be obtained very accurately, from available data, in astronomical units.
However, the length of the astronomical unit in terrestrial dimension standards, like meters or statute miles is rather poorly known; and, therefore, such a measure as the distance from Earth to Mars is rather poorly known in terms of standards like meters or miles.
www.hq.nasa.gov /office/pao/History/conghand/guidance.htm   (2659 words)

 Basic Astronomical Terms
Length of the direct, shortest way between two points or objects; here, commonly the distance of a celestial object from Earth, the Solar System, or the Milky Way Galaxy is considered.
This value defines, at last, the length of a meter, from time units, which are measurable by much higher acuracy than length units.
The distance from which the mean distance of Earth's orbit around the Sun, the astronomical unit (AU), appears under the angle of 1 arc second.
seds.lpl.arizona.edu /messier/xtra/Terms/terms.html   (939 words)

The output from `units' indicates that the jansky is defined to be equal to a fluxunit which in turn is defined to be a certain combination of watts, meters, and hertz.
Units specified on the command line will need to be quoted to protect them from shell interpretation and to group them into two arguments.
Internally, nonlinear units are defined by a pair of functions which convert to and from linear units in the data file, so that an eventual conversion to primitive units is possible.
www.delorie.com /gnu/docs/units/units.man.html   (3783 words)

The distance between two points is the length of a straight line segment between them.
In the case of two locations on Earth, usually the distance along the surface is meant: either "as the crow flies" (along a great circle) or by road, railroad, etc. Distance is sometimes expressed in terms of the time to cover it, for example walking or by car.
In physical space the Euclidean distance is in a way the most natural one, because in this case the length of a rigid body does not change with rotation.
www.brainyencyclopedia.com /encyclopedia/d/di/distance.html   (755 words)

 The Nine Planets Glossary
English astronomer and mathematician who, at the age of 24, was the first person to predict the position of a planetary mass beyond Uranus.
One of the earliest American astronomers of note; rose from poverty and overcame a lack of formal education to become the first director of the Harvard College Observatory where he studied Saturn and (with Lassell) discovered its moon Hyperion.
a planetary orbit) is 1/2 the length of the major axis which is a segment of a line passing thru the foci of the ellipse with endpoints on the ellipse itself.
www.seds.org /nineplanets/nineplanets/help.html   (4842 words)

 Base unit definitions: Second
The unit of time, the second, was defined originally as the fraction 1/86 400 of the mean solar day.
However, measurement showed that irregularities in the rotation of the Earth could not be taken into account by the theory and have the effect that this definition does not allow the required accuracy to be achieved.
In order to define the unit of time more precisely, the 11th CGPM (1960) adopted a definition given by the International Astronomical Union which was based on the tropical year.
physics.nist.gov /cuu/Units/second.html   (163 words)

 Length - Dictionary of Unit - List of Measurement Unit - Dictionary of Length Units
The S I unit of length is the metre.
To change any of these other units of length into their equivalent values in metres use the operation and conversion factor given.
Where some uncertainty is indicated it means that a good idea of the size of the unit can be given but that a better value would depend upon knowing the period and/or culture in which the unit was being used.
www.hobbyprojects.com /dictionary_of_units/length.html   (174 words)

In general English usage, length (symbol: l) is but one particular instance of distance – an object's length is how long the object is – but in the physical sciences and engineering, the word length is in some contexts used synonymously with "distance".
No one speaks of "the length from here to Alpha Centauri", but rather of "the distance from here to Alpha Centauri," but when one speaks of distance more abstractly, one says "A kilometer or a mile, is a unit of length" or "...of distance", and the two statements are synonymous.
Length conversion: millimeters and micrometers to meters and prefixes
www.knowledgefun.com /book/l/le/length.html   (220 words)

 Length units conversion inches mm m mm centimeters meters miles distance kilometers - sengpielaudio
Length units conversion inches mm m mm centimeters meters miles distance kilometers - sengpielaudio
Definition: The length of 1 meter is a SI unit.
Prior to that, the U.S. and Canada each had their own, slightly different definition of the inch in terms of metric units, while the U.K. and other Commonwealth countries defined the inch in terms of the Imperial Standard Yard.
users.nlamerica.com /kevin/Length.htm   (218 words)

 Extrasolar Planets
In the September 15, 1916 issue of The Astronomical Journal (1) and the September 7, 1916 issue of Nature, (2) an article appeared that dealt with the discovery of a rather small, insignificant star that demonstrated a large proper motion.
The planet having the 2.8 mass is considered to be 0.47 astronomical units from the pulsar with a nearly circular orbit.
The 3.4 mass planet is considered to be 0.36 astronomical units from the pulsar with a nearly circular orbit.
www.public.asu.edu /~sciref/exoplnt.htm   (15809 words)

 Length   (Site not responding. Last check: 2007-10-29)
The two fundamental units of length are the foot in English units and the meter in Metric units.
The foot was originally defined as the length of the average person’s foot; however, due to its’ obvious inaccuracy, it was given a formal basis.
The Metric System’s fundamental length unit of the meter was originally defined as the 1/10,000,000 of the distance from the North Pole to the Equator along the meridian line passing through Paris.
www2.latech.edu /~bmagee/303groups/metric_system/length.htm   (133 words)

 [No title]
All units except angular units may be changed in the input file.
For each component a TEMPerature (default units are degrees K) and a physical DIAMeter (default units are solar diameters) must be specified.
In addition, a RADius (default units in astronomical units) in the plane of the sky (before tilting with INCL) and an angular location MODGEN Page 3 THETA (in degrees east from north before rotating with ROT) can be specified.
www.astro.caltech.edu /~tjp/citvlb/vlbhelp/modgen.mem   (911 words)

 Units for Stellar Distances   (Site not responding. Last check: 2007-10-29)
A light year is often a convenient unit in discussing distances between stars, because the average separation between stars in a galaxy is typically of that order of magnitude.
From basic trigonometry we find that this distance is equal to 206,265 astronomical units (where the astronomical unit is the average separation of the Earth and the Sun) or 3.26 light years.
Although the light year is often found in popular level discussions, professional astronomers probably use the parsec, kiloparsec, and megaparsec more commonly as units of large distance.
csep10.phys.utk.edu /astr162/lect/distances/units.html   (531 words)

 J and J Software--Unit Converter
This is a unit converter program written in Python, programmed by Joseph Nicholas.
Units can be sorted alphabetically or by magnitude.
The number of units displayed without having to scroll down is user-adjustable.
www.geocities.com /jandjprograms/unitconverter.html   (329 words)

 Astronomical Leage - Astro Note 16: Astrophotography I - Star Trails
Note that the units of length, L, will be the same as the units of F.
Assuming an 8x enlargement of a print and "normal" viewing distances, a trail of 0.1 mm or less will be virtually unnoticeable.
The angle of sky coverage, B, of any film having linear dimension s used with a lens of focal length F is given by (s and F must have the same units):
www.astroleague.org /al/astrnote/astnot16.html   (214 words)

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