text:
WNBA draft
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The WNBA draft is an annual draft held by the WNBA through which WNBA teams can select new players from a talent pool of college and professional women's basketball players. The first WNBA draft was held in 1997. The WNBA "requires players to be at least 22, to have completed their college eligibility, to have graduated from a four-year college or to be four years removed from high school."[1][2][3]
Contents
[hide]
1 Structure
2 Players selected
2.1 First picks
3 See also
4 References
5 External links
Structure[edit]
The 1997 WNBA draft was divided into three parts. The first part was the initial allocation of 16 players into individual teams. Players such as Cynthia Cooper and Michelle Timms were assigned to different teams. The second part was the WNBA Elite draft, which was composed of professional women's basketball players who had competed in other leagues. The last part would be the 4 rounds of the regular draft.
The next three seasons to follow 1998, 1999 and 2000 would all have expansion drafts. There would not be another expansion draft until the 2006 season.
All seasons before 2002 would carry 4 rounds. Starting with 2003, all drafts would carry 3 rounds.
In 2003 and 2004, there would be dispersal drafts due to the folding of the Cleveland Rockers, Miami Sol and Portland Fire. The players were reallocated to existing teams. There were also dispersal drafts in 2007 with the folding of the Charlotte Sting, 2009 with the shuttering of the Houston Comets, and in 2010 when the Maloofs cast off the Sacramento Monarchs to focus their resources on the Kings franchise in the NBA.
Players selected[edit]
There are no restrictions on what part of the world the players come from (though under varying rules, international players have been subject to tighter age restrictions within the draft than college players). However, college sports governing bodies, most notably the NCAA, prohibit players from competing in professional leagues simultaneously with their college eligibility. Once the player has joined the WNBA, she is eligible to participate in overseas leagues during the WNBA offseason (many WNBA players play in Europe, Australia, or more recently China).
First picks[edit]
See also: List of first overall WNBA draft picks
Dena Head is the oldest #1 draft pick (she was 27 years old), having graduated from the University of Tennessee in 1992 and the first player ever drafted to the WNBA. Lauren Jackson is the youngest #1 draft pick, being drafted at the age of 19. As of 2012, six first picks have gone on to win WNBA Championships, with 12 rings amongst them. In the seventeen seasons that the WNBA has been in existence, eight #1 draft picks have helped lead their teams to a playoff berth in their rookie year.
Year
Player
Country
College/Club
Drafted by
1997 Elite Dena Head United States Tennessee Utah Starzz
1997 Tina Thompson United States USC Houston Comets
1998 Margo Dydek Poland Wychowania Fizycznego (Poland) Utah Starzz
1999 Chamique Holdsclaw1,2 United States Tennessee Washington Mystics
2000 Ann Wauters Belgium Belgium Cleveland Rockers
2001 Lauren Jackson3 Australia Canberra Capitals (Australia) Seattle Storm
2002 Sue Bird2 United States Connecticut Seattle Storm
2003 LaToya Thomas United States Mississippi State Cleveland Rockers
2004 Diana Taurasi 1 United States Connecticut Phoenix Mercury
2005 Janel McCarville[4] United States Minnesota Charlotte Sting
2006 Seimone Augustus1,3 United States LSU Minnesota Lynx
2007 Lindsey Harding United States Duke Phoenix Mercury (traded to Minn.)
2008 Candace Parker1,4 United States Tennessee Los Angeles Sparks
2009 Angel McCoughtry1 United States Louisville Atlanta Dream
2010 Tina Charles1 United States Connecticut Connecticut Sun
2011 Maya Moore1, 2 United States Connecticut Minnesota Lynx
2012 Nneka Ogwumike1 United States Stanford Los Angeles Sparks
2013 Brittney Griner United States Baylor Phoenix Mercury
2014 Chiney Ogwumike1 United States Stanford Connecticut Sun
2015 Jewell Loyd1 United States Notre Dame Seattle Storm
2016 Breanna Stewart1 United States Connecticut Seattle Storm
2017 Kelsey Plum United States Washington San Antonio Stars
2018 Las Vegas Aces
Notes:
1: Won the WNBA Rookie of the Year Award.
2: Started the WNBA All-Star Game in her first season.
3: Made the WNBA All-Star Game as a reserve in her first season.
4: Won the WNBA Most Valuable Player Award in her first season.
Sue Bird, on offense
See also[edit]
WNBA Rookie of the Year Award
References[edit]
"WNBA Past Draft Results Raw Data"
"Dena Head oldest #1"
Jump up ^ Bishop, Greg (June 16, 2009). "Rutgers Basketball Star to Turn Pro in Europe". The New York Times. Retrieved December 6, 2009.
Jump up ^ Analyzing the WNBA's Mandatory Age/Education Policy from a Legal, Cultural, and Ethical Perspective: Women, Men, and the Professional Sports Landscape See Note #100
Jump up ^ Article XIII, Section 1 of the CBA; WNBA CBA
Jump up ^ "WNBA.com:McCarville, White, Irvin Go First in the 2005 WNBA Draft". www.wnba.com. Retrieved 2016-04-16.
External links[edit]
Inside Hoop
WNBA Collective Bargaining Agreement
[show]
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Expansion drafts
First overall picks
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List of Connecticut Huskies in the WNBA Draft
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Lunar distance (astronomy)
From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article is about the average distance from the Earth to the Moon. For its other use in navigation, see Lunar distance (navigation).
A lunar distance, 7008384402000000000♠384402 km, is the Moon's average distance to Earth. The actual distance varies over the course of its orbit. The image compares the Moon's apparent size when it is closest and farthest from Earth.
Lunar distance (LD or Δ ⊕ L {\textstyle \Delta _{\oplus L}} ), also called Earth–Moon distance, Earth–Moon characteristic distance, or distance to the Moon, is a unit of measure in astronomy. It is the average distance from the center of Earth to the center of the Moon. More technically, it is the mean semi-major axis of the geocentric lunar orbit. It may also refer to the time-averaged distance between the centers of the Earth and the Moon, or less commonly, the instantaneous Earth–Moon distance. The lunar distance is approximately a quarter of a million miles.[1]
The mean semi-major axis has a value of 384,402 km (238,856 mi).[2] The time-averaged distance between Earth and Moon centers is 385,000.6 km (239,228.3 mi). The actual distance varies over the course of the orbit of the Moon, from 356,500 km (221,500 mi) at the perigee to 406,700 km (252,700 mi) at apogee, resulting in a differential range of 50,200 km (31,200 mi).[3]
Lunar distance is commonly used to express the distance to near-Earth object encounters.[4] Lunar distance is also an important astronomical datum; the precision of this measurement to a few parts in a trillion has useful implications for testing gravitational theories such as general relativity,[5] and for refining other astronomical values such as Earth mass,[6] Earth radius,[7] and Earth's rotation.[8] The measurement is also useful in characterizing the lunar radius, the mass of the Sun and the distance to the Sun.
Millimeter-precision measurements of the lunar distance are made by measuring the time taken for light to travel between LIDAR stations on the Earth and retroreflectors placed on the Moon. The Moon is spiraling away from the Earth at an average rate of 3.8 cm (1.5 in) per year, as detected by the Lunar Laser Ranging Experiment.[9][10][11] By coincidence, the diameter of corner cubes in retroreflectors on the Moon is also 6998380000000000000♠3.8 cm.[12][13]
Distance between the Earth and Moon - sizes and distance to scale.
Contents
[hide]
1 Value
2 Variation
2.1 Perturbations and eccentricity
2.2 Tidal dissipation
2.3 Orbital history
3 History of measurement
3.1 Parallax
3.1.1 Lunar eclipse
3.1.2 Meridian crossing
3.1.3 Occultations
3.2 Radar
3.3 Laser ranging
3.4 Amateur astronomers and citizen scientists
4 See also
5 External links
6 References
Value[edit]
Lunar distance expressed in selected units
Unit
Mean value
Uncertainty
Ref
meter 7008384402000000000♠3.84402×108 6997110000000000000♠1.1 mm [2]
kilometer 7005384402000000000♠384402 6997110000000000000♠1.1 mm [2]
mile 238,856 0.043 in [2]
Earth radius 60.32 [14]
AU 1/388.6 = 6997256999999999999♠0.00257 [15][16]
light-second 7000128200000000000♠1.282 s 6989375000000000000♠37.5 ps [2]
Variation[edit]
The instantaneous lunar distance is constantly changing. In fact the true distance between the Moon and Earth can change by as much as 7001750000000000000♠75 m/s,[3] or more than 7006100000000000000♠1000 km in just 6 hours, due to its non-circular orbit.[17] There are other effects that also influence the lunar distance. Some factors are described in this section.
Perturbations and eccentricity[edit]
The distance to the Moon can be measured to an accuracy of 6997200000000000000♠2 mm over a 1-hour sampling period,[18] which results in an overall uncertainty of 6998200000000000000♠2–3 cm for the average distance. However, due to its elliptical orbit with varying eccentricity, the instantaneous distance varies with monthly periodicity. Furthermore, the distance is perturbed by the gravitational effects of various astronomical bodies - most significantly the Sun and less so by Jupiter. Other forces responsible for minute perturbations are other planets in the solar system, asteroids, tidal forces, and relativistic effects.[19] The effect of radiation pressure from the sun contributes an amount of ±6997360000000000000♠3.6 mm to the lunar distance.[18]
Although the instantaneous uncertainty is sub-millimeter, the measured lunar distance can change by more than 7007210000000000000♠21000 km from the mean value throughout a typical month. These perturbations are well understood[20] and the lunar distance can be accurately modeled over thousands of years.[19]
The Moon's distance from the Earth and moon phases in 2014.
Moon phases: 0 (1) - new moon, 0.25 - first quarter, 0.5 - full moon, 0.75 - last quarter.
Variation of the distance between the centers of the Moon and the Earth over 700 days.
Tidal dissipation[edit]
Through the action of tidal forces, angular momentum is slowly being transferred from Earth's rotation to the Moon's orbit. The result is that Earth's rate of spin is imperceptibly decreasing (at a rate of 7000229999999999999♠2.3 milliseconds/century),[21] and the lunar orbit is gradually expanding. The current rate of recession is 7000380500000000000♠3.805±0.004 cm per year.[20] However, it is believed that this rate has recently increased, as a rate of 6991120417206325883♠3.8 cm/year would imply that the Moon is only 1.5 billion years old, whereas scientific consensus assumes an age of ~4 billion years.[22] It is also believed that this anomalously high rate of recession may continue to accelerate.[23]
It is predicted that the lunar distance will continue to increase until the Earth and Moon become tidally locked. This would occur when the duration of the lunar orbital period equals the rotational period of Earth. The two bodies will then be at equilibrium, and no further rotational energy will be exchanged. Models predict that 50 billion years would be required to achieve this configuration,[24] which is significantly longer than the expected lifetime of the solar system.
Orbital history[edit]
The average lunar distance is increasing, which implies that the Moon was closer in the past. There is geological evidence that the average lunar distance was about 52 R⊕ during the Precambrian Era; 2,500 million years BP.[22]
The giant impact hypothesis, a widely accepted theory, states that the Moon was created as a result of a catastrophic impact between another planet and Earth, resulting in a re-accumulation of fragments at an initial distance of 3.8 R⊕.[25] In this theory, the initial impact is assumed to have occurred 4.5 billion years ago.[26]
History of measurement[edit]
Until the late 1950s all measurements of lunar distance were based on optical angular measurements. The space age marked a turning point which greatly advanced the precision and accuracy of our knowledge of this value. During the 1950s and 1960s, experiments were conducted that utilized radar, lasers, spacecraft, and computer modeling.[27]
This section is intended to illustrate some of the historically significant or otherwise interesting methods of determining the lunar distance, and is not intended to be an exhaustive or all-encompassing list.
Parallax[edit]
The oldest method of determining the lunar distance involves measuring the angle between the Moon and a chosen reference point from multiple locations, simultaneously. The synchronization can be coordinated by making measurements at a pre-determined time, or during an event which is observable to all parties. Before accurate mechanical chronometers, the synchronization event was typically a lunar eclipse, or the moment when the moon crossed the meridian (if the observers shared the same longitude). This measurement technique is known as lunar parallax.
For increased accuracy, certain systematic errors must be accounted for, such as adjusting the measured angle to account for refraction and distortion of light through the atmosphere.
Lunar eclipse[edit]
Early attempts to measure the distance to the Moon exploited observations of a lunar eclipse combined with knowledge of Earth's radius and an understanding that the Sun is much further than the Moon. By observing the geometry of a lunar eclipse, the lunar distance can be calculated using trigonometry.
The earliest account of an attempt to measure the distance to the Moon using this technique was by the 4th-century-BC Greek astronomer and mathematician Aristarchus of Samos[28] and later by Hipparchus, whose calculations produced a result of 59-67 R⊕.[29] This method later found its way into the work of Ptolemy,[30] who produced a result of 64 1⁄6 R⊕ at its farthest point.[31]
Meridian crossing[edit]
An expedition by French astronomer A.C.D Crommelin observed lunar transits through the meridian (the moment when the Moon crosses an imaginary great circle that passes directly overhead and through the celestial poles) on the same night from two different locations. Careful measurements from 1905 through 1910 measured the angle of elevation at the moment when a specific lunar crater (Mösting A) crossed the meridian, from stations at Greenwich and at Cape of Good Hope, which share nearly the same longitude.[32] A distance was calculated with an uncertainty of ± 30 km, and remained the definitive lunar distance value for the next half century.
Occultations[edit]
By recording the instant when the Moon occults a background star, (or similarly, measuring the angle between the moon and a background star at a predetermined moment) the lunar distance can be determined, as long as the measurements are taken from multiple locations of known separation.
Astronomers O'Keefe and Anderson calculated the lunar distance by observing 4 occultations from 9 locations in 1952.[33] They calculated a mean distance of 7008384407600000000♠384407.6±4.7 km, however the value was refined by in 1962 by Irene Fischer, who incorporated updated geodetic data to produce a value of 7008384403700000000♠384403.7±2 km.[7]
Radar[edit]
An experiment was conducted in 1957 at the U.S. Naval Research Laboratory that used the echo from radar signals to determine the Earth-Moon distance. Radar pulses lasting 6994200000000000000♠2 μs were broadcast from a 7001152400000000000♠50 ft diameter radio dish. After the radio waves echoed off the surface of the Moon, the return signal was detected and the delay time measured. From that measurement, the distance could be calculated. In practice, however, the signal-to-noise ratio was so low that an accurate measurement could not be reliably produced.[34]
The experiment was repeated in 1958 at the Royal Radar Establishment, in England. Radar pulses lasting 6994499999999999999♠5 μs were transmitted with a peak power of 2 megawatts, at a repetition rate of 260 pulses per second. After the radio waves echoed off the surface of the Moon, the return signal was detected and the delay time measured. Multiple signals were added together to obtain a reliable signal by superimposing oscilloscope traces onto photographic film. From the measurements, the distance was calculated with an uncertainty of 7003125000000000000♠1.25 km.[35]
These initial experiments were intended to be proof-of-concept experiments and only lasted one day. Follow-on experiments lasting one month produced a mean value of 7008384402000000000♠384402±1.2 km,[36] which was the most accurate measurement of the lunar distance at the time.
Laser ranging[edit]
An experiment which measured the round-trip time of flight of laser pulses reflected directly off the surface of the Moon was performed in 1962, by a team from Massachusetts Institute of Technology, and a Soviet team at the Crimean Astrophysical Observatory.[37]
During the Apollo missions in 1969, astronauts placed retroreflectors on the surface of the Moon for the purpose of refining the accuracy of this technique. The measurements are ongoing and involve multiple laser facilities. The instantaneous accuracy of the Lunar Laser Ranging experiments can exceed sub-millimeter resolution, and is the most reliable method of determining the lunar distance, to date.
Amateur astronomers and citizen scientists[edit]
Due to the modern accessibility to accurate timing devices, high resolution digital cameras, GPS receivers, powerful computers and near instantaneous communication, it has become possible for amateur astronomers to make high accuracy measurements of the lunar distance.
On May 23, 2007 digital photographs of the Moon during a near-occultation of Regulus were taken from two locations, in Greece and England. By measuring the parallax between the moon and the chosen background star, the lunar distance was calculated.[38]
A more ambitious project called the "Aristarchus Campaign" was conducted during the lunar eclipse of 15 April 2014.[17] During this event, participants were invited to record a series of 5 digital photographs from moonrise through culmination - the point of greatest altitude. The method took advantage of the fact that the Moon is actually closest to an observer when it is at its highest point in the sky, compared to when it is on the horizon. Although it appears that the Moon is biggest when it is near the horizon, the opposite is true. This phenomenon is known as the moon illusion. The reason for the change in distance results from the fact that the distance from the center of the Moon to the center of Earth is nearly constant throughout the night, but an observer on the surface of Earth is actually 1 Earth radius from the center of Earth. This offset brings them closest to the Moon when it is overhead.
Modern cameras have now reached the resolution level capable of capturing the Moon with a precision enough to perceive and more importantly to measure this tiny variation in apparent size. The results of this experiment were calculated as LD = 7001605100000000000♠60.51+3.91
−4.19 R⊕. The accepted value for that night was 60.61, which implied a 7000300000000000000♠3% accuracy. The benefit of this method is that the only measuring equipment needed is a modern digital camera (equipped with an accurate clock, and GPS receiver).
Other experimental methods of measuring the lunar distance that can be performed by amateur astronomers involve:
Taking pictures of the Moon before it enters into the penumbra and after it is completely eclipsed.
Measuring, as precise as possible, the time of the eclipse contacts.
Taking good pictures of the partial eclipse when the shape and size of the Earth shadow is clearly visible.
Taking a picture of the Moon including in the same field of view, Spica and Mars - from various locations.
See also[edit]
Astronomical unit
Ephemeris
Jet Propulsion Laboratory Development Ephemeris
Lunar Laser Ranging Experiment
Lunar theory
On the Sizes and Distances (Aristarchus)
Orbit of the Moon
The Prutenic Tables of Erasmus Reinhold
Supermoon
External links[edit]
Wolfram Alpha widget - Current distance moon earth
References[edit]
Jump up ^ Groten, Erwin (1 April 2004). "Fundamental Parameters and Current (2004) Best Estimates of the Parameters of Common Relevance to Astronomy, Geodesy, and Geodynamics by Erwin Groten, IPGD, Darmstadt" (PDF). Journal of Geodesy. 77 (10–11): 724–797. Bibcode:2004JGeod..77..724.. doi:10.1007/s00190-003-0373-y. Retrieved 2 March 2016.
^ Jump up to: a b c d e Battat, J. B. R.; Murphy, T. W.; Adelberger, E. G. (January 2009). "The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO): Two Years of Millimeter-Precision Measurements of the Earth-Moon Range". Astronomical Society of the Pacific. 121 (875): 29–40. Bibcode:2009PASP..121...29B. doi:10.1086/596748  . JSTOR 10.1086/596748.
^ Jump up to: a b Murphy, T W (1 July 2013). "Lunar laser ranging: the millimeter challenge" (PDF). Reports on Progress in Physics. 76 (7): 2. arXiv:1309.6294  [gr-qc]. Bibcode:2013RPPh...76g6901M. doi:10.1088/0034-4885/76/7/076901.
Jump up ^ "NEO Earth Close Approaches". Neo.jpl.nasa.gov. Archived from the original on 2014-03-07. Retrieved 2016-02-22.
Jump up ^ Williams, J. G.; Newhall, X. X.; Dickey, J. O. (15 June 1996). "Relativity parameters determined from lunar laser ranging" (PDF). Physical Review D. 53 (12): 6730–6739. Bibcode:1996PhRvD..53.6730W. doi:10.1103/PhysRevD.53.6730.
Jump up ^ Shuch, H. Paul (July 1991). "Measuring the mass of the earth: the ultimate moonbounce experiment" (PDF). Proceedings, 25th Conference of the Central States VHF Society. American Radio Relay League: 25–30. Retrieved 28 February 2016.
^ Jump up to: a b Fischer, Irene (August 1962). "Parallax of the moon in terms of a world geodetic system" (PDF). The Astronomical Journal. 67: 373. Bibcode:1962AJ.....67..373F. doi:10.1086/108742.
Jump up ^ Dickey, J. O.; Bender, P. L.; et al. (22 July 1994). "Lunar Laser Ranging: A Continuing Legacy of the Apollo Program" (PDF). Science. 265 (5171): 482–490. Bibcode:1994Sci...265..482D. doi:10.1126/science.265.5171.482. PMID 17781305.
Jump up ^ "Is the Moon moving away from the Earth? When was this discovered? (Intermediate) - Curious About Astronomy? Ask an Astronomer". Curious.astro.cornell.edu. Retrieved 2016-02-22.
Jump up ^ C.D. Murray & S.F. Dermott (1999). Solar System Dynamics. Cambridge University Press. p. 184.
Jump up ^ Dickinson, Terence (1993). From the Big Bang to Planet X. Camden East, Ontario: Camden House. pp. 79–81. ISBN 0-921820-71-2.
Jump up ^ "NASA - Accuracy of Eclipse Predictions". Eclipse.gsfc.nasa.gov. Retrieved 2016-02-22.
Jump up ^ "Lunar Retroreflectors". Physics.ucsd.edu. Retrieved 2016-02-22.
Jump up ^ Lasater, A. Brian (2007). The dream of the West : the ancient heritage and the European achievement in map-making, navigation and science, 1487-1727. Morrisville: Lulu Enterprises. p. 185. ISBN 978-1-4303-1382-3. Retrieved 28 February 2016.
Jump up ^ Leslie, William T. Fox ; illustrated by Clare Walker (1983). At the sea's edge : an introduction to coastal oceanography for the amateur naturalist. Englewood Cliffs, N.J.: Prentice-Hall. p. 101. ISBN 978-0130497833.
Jump up ^ Williams, Dr. David R. (18 November 2015). "Planetary Fact Sheet - Ratio to Earth Values". NASA Goddard Space Flight Center. Retrieved 28 February 2016.
^ Jump up to: a b Zuluaga, Jorge I.; Figueroa, Juan C.; Ferrin, Ignacio (19 May 2014). "The simplest method to measure the geocentric lunar distance: a case of citizen science": (page needed). arXiv:1405.4580  . Bibcode:2014arXiv1405.4580Z.
^ Jump up to: a b Reasenberg, R.D.; Chandler, J.F.; et al. "Modeling and Analysis of the APOLLO Lunar Laser Ranging Data". arXiv:1608.04758  [astro-ph.IM].
^ Jump up to: a b Vitagliano, Aldo (1997). "Numerical integration for the real time production of fundamental ephemerides over a wide time span" (PDF). Celestial Mechanics and Dynamical Astronomy. 66 (3): 293–308. Bibcode:1996CeMDA..66..293V. doi:10.1007/BF00049383.
^ Jump up to: a b Folkner, W. M.; Williams, J. G.; et al. (February 2014). "The Planetary and Lunar Ephemerides DE430 and DE431" (PDF). The Interplanetary Network Progress Report. 42-169.
Jump up ^ Choi, Charles Q. (19 November 2014). "Moon Facts: Fun Information About the Earth's Moon". Space.com. TechMediaNetworks, Inc. Retrieved 3 March 2016.
^ Jump up to: a b Walker, James C. G.; Zahnle, Kevin J. (17 April 1986). "Lunar nodal tide and distance to the Moon during the Precambrian". Nature. 320 (6063): 600–602. Bibcode:1986Natur.320..600W. doi:10.1038/320600a0.
Jump up ^ Bills, B.G. & Ray, R.D. (1999), "Lunar Orbital Evolution: A Synthesis of Recent Results", Geophysical Research Letters, 26 (19): 3045–3048, Bibcode:1999GeoRL..26.3045B, doi:10.1029/1999GL008348
Jump up ^ Cain, Fraser. "WHEN WILL EARTH LOCK TO THE MOON?". Universe Today. Universe Today. Retrieved 1 September 2016.
Jump up ^ Canup, R. M. (17 October 2012). "Forming a Moon with an Earth-like Composition via a Giant Impact". Science. 338 (6110): 1052–1055. Bibcode:2012Sci...338.1052C. doi:10.1126/science.1226073. PMID 23076098.
Jump up ^ "The Theia Hypothesis: New Evidence Emerges that Earth and Moon Were Once the Same". The Daily Galaxy. 2007-07-05. Retrieved 2013-11-13.
Jump up ^ Newhall, X.X; Standish, E.M; Williams, J. G. (Aug 1983). "DE 102 - A numerically integrated ephemeris of the moon and planets spanning forty-four centuries". Astronomy and Astrophysics. 125 (1): 150–167. Bibcode:1983A&A...125..150N. ISSN 0004-6361. Retrieved 28 February 2016.
Jump up ^ Gutzwiller, Martin C. (1998). "Moon–Earth–Sun: The oldest three-body problem". Reviews of Modern Physics. 70 (2): 589–639. Bibcode:1998RvMP...70..589G. doi:10.1103/RevModPhys.70.589.
Jump up ^ Sheehan, William; Westfall, John (2004). The transits of Venus. Amherst, N.Y.: Prometheus Books. pp. 27–28. ISBN 1-59102-175-8. Retrieved 27 February 2016.
Jump up ^ Webb, Stephen (1999), "3.2 Aristarchus, Hipparchus, and Ptolemy", Measuring the Universe: The Cosmological Distance Ladder, Springer, pp. 27–35, ISBN 978-1-85233-106-1 . See in particular p. 33: "Almost everything we know about Hipparchus comes down to us by way of Ptolemy."
Jump up ^ Helden, Albert van (1986). Measuring the universe : cosmic dimensions from Aristarchus to Halley (Repr. ed.). Chicago: University of Chicago Press. p. 16. ISBN 0-226-84882-5.
Jump up ^ Fischer, Irène (7 November 2008). "The distance of the moon". Bulletin géodésique. 71 (1): 37–63. Bibcode:1964BGeod..38...37F. doi:10.1007/BF02526081.
Jump up ^ O'Keefe, J. A.; Anderson, J. P. (1952). "The earth's equatorial radius and the distance of the moon" (PDF). Astronomical Journal. 57: 108–121. Bibcode:1952AJ.....57..108O. doi:10.1086/106720.
Jump up ^ Yaplee, B. S.; Roman, N. G.; Scanlan, T. F.; Craig, K. J. (30 July – 6 August 1958). "A lunar radar study at 10-cm wavelength" (PDF). Paris Symposium on Radio Astronomy. IAU Symposium no. 9. Retrieved 29 February 2016.
Jump up ^ Hey, J. S.; Hughes, V. A. (30 July – 6 August 1958). "Radar observation of the moon at 10-cm wavelength" (PDF). Paris Symposium on Radio Astronomy.
Jump up ^ Yaplee, B. S.; Knowles, S. H.; et al. (January 1965). "The mean distance to the Moon as determined by radar" (PDF). Symposium - International Astronomical Union. 21: 2. doi:10.1017/S0074180900104826.
Jump up ^ Bender, P. L.; Currie, D. G.; Dicke, R. H.; et al. (October 19, 1973). "The Lunar Laser Ranging Experiment" (PDF). Science. 182 (4109): 229–238. Bibcode:1973Sci...182..229B. doi:10.1126/science.182.4109.229. PMID 17749298. Retrieved April 27, 2013.
Jump up ^ Wright, Ernie. "Overhead view of the Earth-Moon system, to scale Lunar Parallax: Estimating the Moon's Distance". Retrieved 29 February 2016.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Lunar_distance_(astronomy)&oldid=812541472"
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Biomolecule
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A representation of the 3d structure of myoglobin, showing alpha helices, represented by ribbons. This protein was the first to have its structure solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a Nobel Prize in Chemistry
A biomolecule or biological molecule is a loosely used term for molecules or more commonly ions that are present in organisms. Biomolecules including large macromolecules (or polyanions) such as proteins, carbohydrates, lipids, and nucleic acids, as well as small molecules such as primary metabolites, secondary metabolites, and natural products. A more general name for this class of material is biological materials. Biomolecules are usually endogenous but may also be exogenous. For example, pharmaceutical drugs may be natural products or semisynthetic (biopharmaceuticals) or they may be totally synthetic.
Biology and its subsets of biochemistry and molecular biology study biomolecules and their reactions. Most biomolecules are organic compounds, and just four elements—oxygen, carbon, hydrogen, and nitrogen—make up 96% of the human body's mass. But many other elements, such as the various biometals, are present in small amounts.
The uniformity of specific types of molecules (the biomolecules) and of some metabolic pathways as invariant features between the diversity of life forms is called "biochemical universals"[1] or "theory of material unity of the living beings", a unifying concept in biology, along with cell theory and evolution theory.[2]
Contents
[hide]
1 Types of biomolecules
2 Nucleosides and nucleotides
2.1 DNA and RNA structure
3 Saccharides
4 Lignin
5 Lipids
6 Amino acids
6.1 Protein structure
6.1.1 Apoenzymes
6.1.2 Isoenzymes
7 See also
8 References
9 External links
Types of biomolecules[edit]
A diverse range of biomolecules exist, including:
Small molecules:
Lipids, fatty acids, glycolipids, sterols, gs
Vitamins
Hormones, neurotransmitters
Metabolites
Monomers, oligomers and polymers:
Biomonomers
Bio-oligo
Biopolymers
Polymerization process
Covalent bond name between monomers
Amino acids Oligopeptides Polypeptides, proteins (hemoglobin...) Polycondensation Peptide bond
Monosaccharides Oligosaccharides Polysaccharides (cellulose...) Polycondensation Glycosidic bond
Isoprene Terpenes Polyterpenes: cis-1,4-polyisoprene natural rubber and trans-1,4-polyisoprene gutta-percha Polyaddition
Nucleotides Oligonucleotides Polynucleotides, nucleic acids (DNA, RNA) Phosphodiester bond
Nucleosides and nucleotides[edit]
Main articles: Nucleosides and Nucleotides
Nucleosides are molecules formed by attaching a nucleobase to a ribose or deoxyribose ring. Examples of these include cytidine (C), uridine (U), adenosine (A), guanosine (G), thymidine (T) and inosine (I).
Nucleosides can be phosphorylated by specific kinases in the cell, producing nucleotides. Both DNA and RNA are polymers, consisting of long, linear molecules assembled by polymerase enzymes from repeating structural units, or monomers, of mononucleotides. DNA uses the deoxynucleotides C, G, A, and T, while RNA uses the ribonucleotides (which have an extra hydroxyl(OH) group on the pentose ring) C, G, A, and U. Modified bases are fairly common (such as with methyl groups on the base ring), as found in ribosomal RNA or transfer RNAs or for discriminating the new from old strands of DNA after replication.[3]
Each nucleotide is made of an acyclic nitrogenous base, a pentose and one to three phosphate groups. They contain carbon, nitrogen, oxygen, hydrogen and phosphorus. They serve as sources of chemical energy (adenosine triphosphate and guanosine triphosphate), participate in cellular signaling (cyclic guanosine monophosphate and cyclic adenosine monophosphate), and are incorporated into important cofactors of enzymatic reactions (coenzyme A, flavin adenine dinucleotide, flavin mononucleotide, and nicotinamide adenine dinucleotide phosphate).[4]
DNA and RNA structure[edit]
Main articles: DNA and RNA structure
DNA structure is dominated by the well-known double helix formed by Watson-Crick base-pairing of C with G and A with T. This is known as B-form DNA, and is overwhelmingly the most favorable and common state of DNA; its highly specific and stable base-pairing is the basis of reliable genetic information storage. DNA can sometimes occur as single strands (often needing to be stabilized by single-strand binding proteins) or as A-form or Z-form helices, and occasionally in more complex 3D structures such as the crossover at Holliday junctions during DNA replication.[4]
Stereo 3D image of a group I intron ribozyme (PDB file 1Y0Q); gray lines show base pairs; ribbon arrows show double-helix regions, blue to red from 5' to 3' end; white ribbon is an RNA product.
RNA, in contrast, forms large and complex 3D tertiary structures reminiscent of proteins, as well as the loose single strands with locally folded regions that constitute messenger RNA molecules. Those RNA structures contain many stretches of A-form double helix, connected into definite 3D arrangements by single-stranded loops, bulges, and junctions.[5] Examples are tRNA, ribosomes, ribozymes, and riboswitches. These complex structures are facilitated by the fact that RNA backbone has less local flexibility than DNA but a large set of distinct conformations, apparently because of both positive and negative interactions of the extra OH on the ribose.[6] Structured RNA molecules can do highly specific binding of other molecules and can themselves be recognized specifically; in addition, they can perform enzymatic catalysis (when they are known as "ribozymes", as initially discovered by Tom Cech and colleagues.[7]
Saccharides[edit]
Monosaccharides are the simplest form of carbohydrates with only one simple sugar. They essentially contain an aldehyde or ketone group in their structure.[8] The presence of an aldehyde group in a monosaccharide is indicated by the prefix aldo-. Similarly, a ketone group is denoted by the prefix keto-.[3] Examples of monosaccharides are the hexoses, glucose, fructose, Trioses, Tetroses, Heptoses, galactose, pentoses, ribose, and deoxyribose. Consumed fructose and glucose have different rates of gastric emptying, are differentially absorbed and have different metabolic fates, providing multiple opportunities for 2 different saccharides to differentially affect food intake.[8] Most saccharides eventually provide fuel for cellular respiration.
Disaccharides are formed when two monosaccharides, or two single simple sugars, form a bond with removal of water. They can be hydrolyzed to yield their saccharin building blocks by boiling with dilute acid or reacting them with appropriate enzymes.[3] Examples of disaccharides include sucrose, maltose, and lactose.
Polysaccharides are polymerized monosaccharides, or complex carbohydrates. They have multiple simple sugars. Examples are starch, cellulose, and glycogen. They are generally large and often have a complex branched connectivity. Because of their size, polysaccharides are not water-soluble, but their many hydroxy groups become hydrated individually when exposed to water, and some polysaccharides form thick colloidal dispersions when heated in water.[3] Shorter polysaccharides, with 3 - 10 monomers, are called oligosaccharides.[9] A fluorescent indicator-displacement molecular imprinting sensor was developed for discriminating saccharides. It successfully discriminated three brands of orange juice beverage.[10] The change in fluorescence intensity of the sensing films resulting is directly related to the saccharide concentration.[11]
Lignin[edit]
Lignin is a complex polyphenolic macromolecule composed mainly of beta-O4-aryl linkages. After cellulose, lignin is the second most abundant biopolymer and is one of the primary structural components of most plants. It contains subunits derived from p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol[12] and is unusual among biomolecules in that it is racemic. The lack of optical activity is due to the polymerization of lignin which occurs via free radical coupling reactions in which there is no preference for either configuration at a chiral center.
Lipids[edit]
Lipids (oleaginous) are chiefly fatty acid esters, and are the basic building blocks of biological membranes. Another biological role is energy storage (e.g., triglycerides). Most lipids consist of a polar or hydrophilic head (typically glycerol) and one to three nonpolar or hydrophobic fatty acid tails, and therefore they are amphiphilic. Fatty acids consist of unbranched chains of carbon atoms that are connected by single bonds alone (saturated fatty acids) or by both single and double bonds (unsaturated fatty acids). The chains are usually 14-24 carbon groups long, but it is always an even number.
For lipids present in biological membranes, the hydrophilic head is from one of three classes:
Glycolipids, whose heads contain an oligosaccharide with 1-15 saccharide residues.
Phospholipids, whose heads contain a positively charged group that is linked to the tail by a negatively charged phosphate group.
Sterols, whose heads contain a planar steroid ring, for example, cholesterol.
Other lipids include prostaglandins and leukotrienes which are both 20-carbon fatty acyl units synthesized from arachidonic acid. They are also known as fatty acids
Amino acids[edit]
Amino acids contain both amino and carboxylic acid functional groups. (In biochemistry, the term amino acid is used when referring to those amino acids in which the amino and carboxylate functionalities are attached to the same carbon, plus proline which is not actually an amino acid).
Modified amino acids are sometimes observed in proteins; this is usually the result of enzymatic modification after translation (protein synthesis). For example, phosphorylation of serine by kinases and dephosphorylation by phosphatases is an important control mechanism in the cell cycle. Only two amino acids other than the standard twenty are known to be incorporated into proteins during translation, in certain organisms:
Selenocysteine is incorporated into some proteins at a UGA codon, which is normally a stop codon.
Pyrrolysine is incorporated into some proteins at a UAG codon. For instance, in some methanogens in enzymes that are used to produce methane.
Besides those used in protein synthesis, other biologically important amino acids include carnitine (used in lipid transport within a cell), ornithine, GABA and taurine.
Protein structure[edit]
The particular series of amino acids that form a protein is known as that protein's primary structure. This sequence is determined by the genetic makeup of the individual. It specifies the order of side-chain groups along the linear polypeptide "backbone".
Proteins have two types of well-classified, frequently occurring elements of local structure defined by a particular pattern of hydrogen bonds along the backbone: alpha helix and beta sheet. Their number and arrangement is called the secondary structure of the protein. Alpha helices are regular spirals stabilized by hydrogen bonds between the backbone CO group (carbonyl) of one amino acid residue and the backbone NH group (amide) of the i+4 residue. The spiral has about 3.6 amino acids per turn, and the amino acid side chains stick out from the cylinder of the helix. Beta pleated sheets are formed by backbone hydrogen bonds between individual beta strands each of which is in an "extended", or fully stretched-out, conformation. The strands may lie parallel or antiparallel to each other, and the side-chain direction alternates above and below the sheet. Hemoglobin contains only helices, natural silk is formed of beta pleated sheets, and many enzymes have a pattern of alternating helices and beta-strands. The secondary-structure elements are connected by "loop" or "coil" regions of non-repetitive conformation, which are sometimes quite mobile or disordered but usually adopt a well-defined, stable arrangement.[13]
The overall, compact, 3D structure of a protein is termed its tertiary structure or its "fold". It is formed as result of various attractive forces like hydrogen bonding, disulfide bridges, hydrophobic interactions, hydrophilic interactions, van der Waals force etc.
When two or more polypeptide chains (either of identical or of different sequence) cluster to form a protein, quaternary structure of protein is formed. Quaternary structure is an attribute of polymeric (same-sequence chains) or heteromeric (different-sequence chains) proteins like hemoglobin, which consists of two "alpha" and two "beta" polypeptide chains.
Apoenzymes[edit]
An apoenzyme (or, generally, an apoprotein) is the protein without any small-molecule cofactors, substrates, or inhibitors bound. It is often important as an inactive storage, transport, or secretory form of a protein. This is required, for instance, to protect the secretory cell from the activity of that protein. Apoenzymes becomes active enzymes on addition of a cofactor. Cofactors can be either inorganic (e.g., metal ions and iron-sulfur clusters) or organic compounds, (e.g., flavin and heme). Organic cofactors can be either prosthetic groups, which are tightly bound to an enzyme, or coenzymes, which are released from the enzyme's active site during the reaction.
Isoenzymes[edit]
Isoenzymes, or isozymes, are multiple forms of an enzyme, with slightly different protein sequence and closely similar but usually not identical functions. They are either products of different genes, or else different products of alternative splicing. They may either be produced in different organs or cell types to perform the same function, or several isoenzymes may be produced in the same cell type under differential regulation to suit the needs of changing development or environment. LDH (lactate dehydrogenase) has multiple isozymes, while fetal hemoglobin is an example of a developmentally regulated isoform of a non-enzymatic protein. The relative levels of isoenzymes in blood can be used to diagnose problems in the organ of secretion .
See also[edit]
Molecular and cellular biology portal
Biomolecular engineering
List of biomolecules
Metabolism
Molecular biology
Multi-state modeling of biomolecules
References[edit]
Jump up ^ Green, D.E. & Goldberger, R. Molecular Insights into the Living Process. Academic Press, New York, 1967, link.
Jump up ^ Gayon, J. La philosophie et la biologie. In: Encyclopédie philosophique universelle, vol. IV, Le Discours philosophique, ss dir. J.F. Mattéi, Presses Universitaires de France, 1998, pp. 2152-2171, link.
^ Jump up to: a b c d Slabaugh, Michael R. & Seager, Spencer L. (2007). Organic and Biochemistry for Today (6th ed.). Pacific Grove: Brooks Cole. ISBN 0-495-11280-1.
^ Jump up to: a b Alberts B, Johnson A, Lewis J, Raff M, Roberts K & Wlater P (2002). Molecular biology of the cell (4th ed.). New York: Garland Science. pp. 120–1. ISBN 0-8153-3218-1.
Jump up ^ Saenger W (1984). Principles of Nucleic Acid Structure. Springer-Verlag. ISBN 0387907629.
Jump up ^ Richardson JS, Schneider B, Murray LW, Kapral GJ, Immormino RM, Headd JJ, Richardson DC, Ham D, Hershkovits E, Williams LD, Keating KS, Pyle AM, Micallef D, Westbrook J, Berman HM (2008). "RNA Backbone: Consensus all-angle conformers and modular string nomenclature". RNA. 14: 465–481. doi:10.1261/rna.657708. PMC 2248255  . PMID 18192612.
Jump up ^ Kruger K, Grabowski PJ, Zaug AJ, Sands J, Gottschling DE, Cech TR (1982). "Self-splicing RNA: autoexcision and autocyclization of the ribosomal RNA intervening sequence of Tetrahymena". Cell. 31: 147–157. doi:10.1016/0092-8674(82)90414-7. PMID 6297745.
^ Jump up to: a b Peng, Bo & Yu Qin (June 2009). "Fructose and Satiety". Journal of Nutrition: 6137–42.
Jump up ^ Pigman, W.; D. Horton (1972). The Carbohydrates. 1A. San Diego: Academic Press. p. 3. ISBN 978-0-12-395934-8.
Jump up ^ Jin, Tan; Wang He-Fang & Yan Xiu-Ping (2009). "Discrimination of Saccharides with a Fluorescent Molecular Imprinting Sensor Array Based on Phenylboronic Acid Functionalized Mesoporous Silica". Anal. Chem. 81 (13): 5273–80. doi:10.1021/ac900484x. PMID 19507843.
Jump up ^ Bo Peng & Yu Qin (2008). "Lipophilic Polymer Membrane Optical Sensor with a Synthetic Receptor for Saccharide Detection". Anal. Chem. 80 (15): 6137–41. doi:10.1021/ac800946p. PMID 18593197.
Jump up ^ K. Freudenberg; A.C. Nash, eds. (1968). Constitution and Biosynthesis of Lignin. Berlin: Springer-Verlag.
Jump up ^ Richardson, JS (1981). "The Anatomy and Taxonomy of Proteins". Advances in Protein Chemistry. 34: 167–339 [1]. doi:10.1016/S0065-3233(08)60520-3. PMID 7020376.
External links[edit]
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