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# Topic: Astronomical unit

###### In the News (Fri 24 Nov 17)

 Astronomical unit - Wikipedia, the free encyclopedia For greater precision, the International Astronomical Union in 1976 defined the AU as the distance from the centre of 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. en.wikipedia.org /wiki/Astronomical_unit   (939 words)

 Astronomical distance - Wikipedia, the free encyclopedia The distance to an astronomical body is often, therefore, referred to by the time it takes light to reach the body. Another often used unit, on the same order of magnitude as the light year is the parsec. In the early 1900s an astronomer named Henrietta Leavitt examined the relationship between the absolute magnitude and period of the variable stars known as Cepheid variables. en.wikipedia.org /wiki/Astronomical_distance   (447 words)

 astronomical unit articles on Encyclopedia.com   (Site not responding. Last check: 2007-10-22) The astronomical unit is the principal unit of measurement within the solar system, e.g., Mercury is just over 1/3 AU and Pluto is about 39 AU from the sun. Typical examples are devices used in astronomical telescopes to measure the apparent diameter of celestial objects and similar devices used in microscopes. Its average distance from the sun is 2.36 astronomical units, and the period of its orbit is 1,325 days. www.encyclopedia.com /articles/00847.html   (487 words)

 NationMaster - Encyclopedia: Astronomical unit   (Site not responding. Last check: 2007-10-22) The aberration of light (also referred to as astronomical aberration or stellar aberration) is an astronomical phenomenon which produces an apparent motion of celestial objects. 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). Distance measurements began with astronomers of the renaissance using parallax across the face of the earth to determine the distance to nearby heavenly bodies. www.nationmaster.com /encyclopedia/Astronomical-unit   (2666 words)

 CD Baby: ASTRONOMICAL UNIT: Astronomical Unit   (Site not responding. Last check: 2007-10-22) Astronomical Unit is a group of four musicians who use their talents and abilities in the eternal pursuit of funkiness. Astronomical Unit has been performing for several years with Bill "Greezy Fingers" Smith on keyboards, alto sax and vocals; Dave "Super T" Tran on guitar, percussion and vocals; Andy "Dr. Gravymaster" Mandiak on bass; and Brian "Soup Kitchen" Platino on drums and percussion. All songs written by Astronomical Unit are a collaboration of several band members with eclectic tastes in music which gives each tune its own vibe, yet all have a similar focus: to shake booties whenever and wherever possible. www.cdbaby.com /cd/astronomicalunit   (213 words)

 The Astronomical Unit (AU): Mercury/Sun Distance The astronomical unit (AU) currently in use is derived from the average mean distance between the Earth and the Sun, which is generally cited as 93,000,000 miles or 1,496,000,000 kilometers. It does not seem at all acceptable to employ the Earth/Sun distance for the astronomical unit of measurement, given the fact that it lies somewhere within the system, not as one of the system's defining or manifest parameters, by itself determined by those parameters. Other appear when Mercury is simply taken as the basic unit of measurement for other aspects, such as degrees of tilt in the axes of the planets and with respect to the plane of the ecliptic of Earth. www.earthmatrix.com /orbital/astronomical_unit.html   (1297 words)

 SurfWax: News, Reviews and Articles On Astronomical Unit The spacecraft crossed at 94 astronomical units (an astronomical unit is the distance from the Sun to Earth), or 14... Currently about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), the planet becomes the farthest-known object in the solar system, and the third brightest of the Kuiper belt objects. One astronomical unit is the distance from Earth to the sun, which is 150 million kilometers (93 million miles)... news.surfwax.com /astronomy/files/Astronomical_Unit_Astronomy.html   (3354 words)

 Talk:Astronomical unit - Wikipedia, the free encyclopedia The astronomical unit is defined as the mean distance between the Earth and the Sun. The best measurement of the astronomical unit comes from phase-modulated continuous-wave radio signals reflected off other planets. It was continuous-wave signals returned from the Viking probes on Mars that allowed the determination of the astronomical unit to 20m. en.wikipedia.org /wiki/Talk:Astronomical_unit   (542 words)

 NationMaster - Encyclopedia: Astronomical unit   (Site not responding. Last check: 2007-10-22) Standards are produced by many organizations, some for internal usage only, others for use by a groups of people, groups of companies, or a subsection of an industry. A light minute (also written light-minute) is a unit of length. A light hour (also written light-hour) is a unit of length. www.nationmaster.com /encyclopedia/astronomical-unit   (2666 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)

 Astronomical unit   (Site not responding. Last check: 2007-10-22) Earth's orbit is not a circle but an ellipse ; originally, the AU was defined as the length of the semimajor axis of said orbit. A conversion to SI units would separate the results from the gravitational constant, at the cost ofintroducing additional uncertainty by assigning a specific value to that unknown constant. It is known that the mass of the Sun is very slowly decreasing, and therefore the period of a body at a given distance isincreasing. www.therfcc.org /astronomical-unit-31190.html   (525 words)

 Astronomical unit (Henry Spencer)   (Site not responding. Last check: 2007-10-22) From: Henry Spencer Newsgroups: sci.space.science Subject: Re: Astronomical Units Date: Tue, 24 Mar 1998 05:31:13 GMT In article <6f1ud3\$7rj@lace.colorado.edu>, Frank Crary wrote: >...If you mean using the distance between the Earth and the Sun as a unit >of length, then the use is ancient... In particular, he originated the idea of putting together a complete system of units -- for calculations, not just results -- with the AU as the unit of length, the day as the unit of time, and the Sun's mass as the unit of mass, with constants (notably the constant of gravity) adjusted to match. Almost certainly "astronomical unit" is an English translation of whatever term he used. www.yarchive.net /space/science/astronomical_unit.html   (399 words)

 Astronomical unit   (Site not responding. Last check: 2007-10-22) While the value of the astronomical unit now known to great precision the value the mass of the Sun is not of uncertainty in the value of the gravitational constant. Because the gravitational constant is known only five or six significant digits while positions of the planets are known to or 12 digits calculations in celestial mechanics typically performed in solar masses and astronomical rather than in kilograms and kilometers. This makes all results dependent on the gravitational A conversion to SI units would separate the results from the constant at the cost of introducing additional by assigning a specific value to that constant. www.freeglossary.com /Astronomical_unit   (839 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. English astronomer who applied Newton's laws of motion to historical comet data and predicted correctly the reappearance of the comet which now bears his name. www.seds.org /nineplanets/nineplanets/help.html   (4842 words)

 Astronomical Unit   (Site not responding. Last check: 2007-10-22) The aging Sun-like star HD 69830 has three planets and an asteroid belt orbiting it less than 1 astronomical unit away. The astronomical unit (AU) is a unit of distance, approximately equal to the mean distance between Earth and Sun. It is known that the mass of the Sun is very slowly decreasing, and therefore the period of a body at a given distance is increasing. www.wikiverse.org /astronomical-unit   (737 words)

 astronomical unit   (Site not responding. Last check: 2007-10-22) 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)

 Star tracks. (Thousand Astronomical Unit project) - Science News - HighBeam Research   (Site not responding. Last check: 2007-10-22) It is probably the oldest astronomical activity, having begun the first time an observer made note of the location a star accurately enough to be able to find it the next night. Called TAU for Thousand Astronomical Unit project, the proposed flight would take a telescope out to 1,000 astronomical units--1,000 times the mean radius of the earth's orbit, or about 93 billion miles. As astronomers know the dimensions of the earth's orbit, they can calculate the altitude of the triangle, which is the distance to the star. highbeam.com /doc/1G1:4722670/Star+tracks.+(Thousand+Astronomical+...   (1979 words)

 astronomical unit concept from the Astronomy knowledge base   (Site not responding. Last check: 2007-10-22) has definition The AU is the preferred unit for distances within the solar system. Mercury, the innermost planet, lies on average 0.39 AU from the Sun; Pluto, normally the farthest planet, lies on average 39.5 AU from the Sun. The astronomical unit is defined as the length of the radius of the unperturbed circular orbit of a body of negligible mass moving around the Sun with a sidereal angular velocity of 0.017202098950 radian per day of 86400 ephemeris seconds. www.site.uottawa.ca:4321 /astronomy/astronomicalunit.html   (219 words)

 Astronomical unit   (Site not responding. Last check: 2007-10-22) ASTRONOMICAL UNIT (AU) 1 AU = 149,597,870.691 kilometers. Definition: An Astronomical Unit is approximately the mean distance between the Earth and the Sun. The Answer The Astronomical Unit is the average distance between the Sun... www.logicjungle.com /wiki/Astronomical_unit   (235 words)

 Astronomical unit   (Site not responding. Last check: 2007-10-22) TASOS is the largest astronomical organization in Singapore with over 200 members plus affiliation with a dozen of schools and institutions all over the country. Sends its subscribers a daily email on astronomical events such as satellite passes and meteor showers that can be observed from their location. A bibliography from the Astronomical Society of the Pacific, for those who want to examine with a skeptical eye some of the claims at the fringes of science that seem connected to astronomy. www.omniknow.com /common/wiki.php?in=en&term=Astronomical_unit   (2038 words)

 Astronomical Unit The Astronomical Unit is the average distance between the Sun and Earth. Kepler's laws relate the period of a planet's orbit (in years) to the average distance of the planet to the Sun in (astronomical units). By sending radio signals (which travel at the speed of light) to a spacecraft, and measuring how long it takes for the spacecraft to return those signals, you can determine how far away a spacecraft is in kilometers. imagine.gsfc.nasa.gov /docs/ask_astro/answers/980122b.html   (293 words)

 astronomical unit on Encyclopedia.com   (Site not responding. Last check: 2007-10-22) A Herald Exclusive; An urban retreat in the North End; Hanover Street unit is quite impressive.(Real... ASTRONOMICAL UNIT [astronomical unit] (AU), mean distance between the earth and sun; one AU is c.92,960,000 mi (149,604,970 km). Piers Pommeroy may well be an expert in risk assessment, but the odds that he'd make a successful bookie are astronomical. www.encyclopedia.com /html/a1/astronomU1.asp   (276 words)

 Solar Mass Loss, the Astronomical Unit, and the Scale of the Solar System   (Site not responding. Last check: 2007-10-22) The new definition would have to be: "The Astronomical Unit is defined as the radius of a circular orbit, in which a body of negligible mass, and free of perturbations, would revolve around a body whose mass is one solar mass unit in 2 To compare with experiment, the numbers of immediate interest are the variations of the semi-major axes of planetary orbits as compared with the estimated error in the AU, as well as secular corrections to the mean motion, namely changes in the period and mean anomaly. When multiplied by the present orbital semi-major axes of the planets Mercury, Venus, Earth and Mars, and the number of orbits in a century, Eq.(18) yields displacements along the orbit in one century of -1380 m, -1009 m, -858 m, and -695 m, respectively. home.comcast.net /~pdnoerd/SMassLoss.html   (3128 words)

 Parallax The average distance between the Earth and the Sun is a natural distance unit and is called an Astronomical Unit (AU). Magnitude is a historical unit of stellar brightness and is defined such that a change of 5 magnitudes represents a factor of 100 in intensity. First magnitude was supposed to be the brightness of the brightest stars, but with quantitative measurement some stars were found to be brighter than those used for the standard. hyperphysics.phy-astr.gsu.edu /hbase/astro/para.html   (437 words)

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