Astronomy/Units

< Astronomy

A unit, especially in astronomy, is often a quantity chosen as a standard in terms of which quantities may be expressed.

Notations

Each unit so chosen is likely to have a sign, symbol, or notation to represent the quantity.

Astronomy

"The International Astronomical Union (IAU) is responsible for maintaining and approving a special set of units in astronomy, formally defined in 1976. One of the most important of these is the astronomical unit. It is a unit of length approximating the Sun-Earth distance (of about 150 million kilometres) which is of convenient use in astronomy. According to its definition adopted by the XXVIIIth General Asssembly of the IAU (IAU 2012 Resolution B2), the astronomical unit is a conventional unit of length equal to 149 597 870 700 m exactly. This definition is valid irrespective of the used time scale. The unique symbol for the astronomical unit is au. The IAU also defines other astronomical units: the astronomical unit of time is 1 day (d) of 86,400 SI seconds (s) (SI is the International System of Units) and the astronomical unit of mass is equal to the mass of the Sun, 1.9891 × 1030 kg."[1]

"Beyond the Solar System the distances in astronomy are so great that using the au becomes too cumbersome. The IAU recognises several other distance units to be used on different scales. For studies of the structure of the Milky Way, our local galaxy, the parsec (pc) is the usual choice. This is equivalent to about 30.857 × 1012 km, or about 206,000 aus, and is itself defined in terms of the au – as the distance at which one Astronomical Unit subtends an angle of one arcsecond. Alternatively the light-year (ly) is sometimes used in scientific papers as a distance unit, although its use is mostly confined to popular publications and similar media. The light-year is roughly equivalent to 0.3 parsecs, and is equal to the distance traveled by light in one Julian year in a vacuum, according to the IAU. To think of it in easily accessible terms, the light-year is 9,460,730,472,580.8 km or 63,241 au. While smaller than the parsec, it is still an incredibly large distance."[1]

"Defining a unit is often more complex than first appears. For instance, to define a light-year it is necessary to understand exactly what a year is. When referring to a year in the precisely defined astronomical sense, it should be written with the indefinite article “a” as “a year”. Although there are several different kinds of year, the IAU regards a year as a Julian year of 365.25 days (31.5576 million seconds) unless otherwise specified. The IAU also recognises a Julian century of 36,525 days in the fundamental formulas for precession (more info). Other measurements of time such as sidereal, solar and universal time are not suitable for measuring precise intervals of time, since the rate of rotation of Earth, on which they ultimately depend, is variable with respect to the second."[1]

Theoretical radiation astronomy

Def. a "standard measure of a quantity"[2] is called a unit.

Research

Hypothesis:

  1. Units have changed over time.

Control groups

This is an image of a Lewis rat. Credit: Charles River Laboratories.

The findings demonstrate a statistically systematic change from the status quo or the control group.

“In the design of experiments, treatments [or special properties or characteristics] are applied to [or observed in] experimental units in the treatment group(s).[3] In comparative experiments, members of the complementary group, the control group, receive either no treatment or a standard treatment.[4]"[5]

Proof of concept

Def. a “short and/or incomplete realization of a certain method or idea to demonstrate its feasibility"[6] is called a proof of concept.

Def. evidence that demonstrates that a concept is possible is called proof of concept.

The proof-of-concept structure consists of

  1. background,
  2. procedures,
  3. findings, and
  4. interpretation.[7]

See also

References

  1. 1 2 3 P. K. Seidelmann (1992). "Measuring the Universe, The IAU and astronomical units". International Astronomical Union. Retrieved 2015-08-09.
  2. ↑ "unit, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 24 July 2015. Retrieved 2015-08-09.
  3. ↑ Klaus Hinkelmann, Oscar Kempthorne (2008). Design and Analysis of Experiments, Volume I: Introduction to Experimental Design (2nd ed.). Wiley. ISBN 978-0-471-72756-9. http://books.google.com/?id=T3wWj2kVYZgC&printsec=frontcover.
  4. ↑ R. A. Bailey (2008). Design of comparative experiments. Cambridge University Press. ISBN 978-0-521-68357-9. http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=9780521683579.
  5. ↑ "Treatment and control groups, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. May 18, 2012. Retrieved 2012-05-31.
  6. ↑ "proof of concept, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. November 10, 2012. Retrieved 2013-01-13.
  7. ↑ Ginger Lehrman and Ian B Hogue, Sarah Palmer, Cheryl Jennings, Celsa A Spina, Ann Wiegand, Alan L Landay, Robert W Coombs, Douglas D Richman, John W Mellors, John M Coffin, Ronald J Bosch, David M Margolis (August 13, 2005). "Depletion of latent HIV-1 infection in vivo: a proof-of-concept study". Lancet 366 (9485): 549-55. doi:10.1016/S0140-6736(05)67098-5. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1894952/. Retrieved 2012-05-09.

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