Editing Asaph Hall (section)

==Biography==
Hall was born in [[Goshen, Connecticut]], the son of Asaph Hall II (1800–42), a clockmaker, and Hannah Palmer (1804–80). His paternal grandfather [[Asaph Hall I]] (June 11, 1735 – March 29, 1800) was a Revolutionary War officer and Connecticut state legislator.<ref>Connecticut Revolutionary War Lists, 1775–1783. p. 20.</ref><ref>Heads of families at the first U.S. census. Ct. By U.S. Bureau of the Census. Washington, 1908. (227p.): 45 Record of Conn. Men in mil. and naval service during the Rev. War, 1775–1783. By Henry P.Johnston. Hartford. 1889. (17,779p.): 61, 424, 548</ref>  His father died when he was 13, leaving the family in financial difficulty, so Hall left school at 16 to become an apprentice to a carpenter. He later enrolled at the [[New-York Central College, McGrawville|New-York Central College]] in [[McGraw, New York|McGrawville, New York]], where he studied mathematics. There he took classes from an instructor of geometry and German, [[Angeline Stickney]]. In 1856 they married.

In 1856, Hall took a job at the [[Harvard College Observatory]] in [[Cambridge, Massachusetts]], and turned out to be an expert computer of orbits. Hall became assistant astronomer at the [[US Naval Observatory]] in [[Washington, D.C.]] in 1862, and within a year of his arrival he was made professor.

On June 5, 1872 Hall published an article entitled "On an experimental determination of <math>\pi</math>" in the journal ''[[Messenger of Mathematics]]''.<ref>{{cite journal|journal=Messenger of Mathematics|first=Asaph|last=Hall|date=1873|oclc=2448539|title=On an experimental determination of <math>\pi</math>|pages=113–114|volume=2|url=https://gdz.sub.uni-goettingen.de/id/PPN599484047_0002?tify=%7B%22pages%22%3A%5B123%5D%2C%22view%22%3A%22info%22%7D}}</ref> In this article, Hall reported the results of an experiment in random sampling that Hall had persuaded his friend, Captain O.C. Fox, to perform when Fox was recuperating from a wound received at the [[Second Battle of Bull Run]]. The experiment involved repetitively throwing at random a fine steel wire onto a plane wooden surface ruled with equidistant parallel lines. An approximation of <math>\pi</math> was then computed as <math>2ml/an</math>, where <math>m</math> is the number of trials, <math>l</math> is the length of the steel wire, <math>a</math> is the distance between parallel lines, and <math>n</math> is the number of intersections. This paper, an experiment on [[Buffon's needle]] problem, is a very early documented use of random sampling (which [[Nicholas Metropolis]] would name the [[Monte Carlo method]] during the [[Manhattan Project]] of [[World War II]]) in scientific inquiry.

In 1875 Hall was given responsibility for the [[USNO]] 26-inch (66-cm) telescope, the largest [[refracting telescope]] in the world at the time. It was with this telescope that he discovered Phobos and Deimos in August 1877. Hall also noticed a white spot on Saturn which he used as a marker to ascertain the planet's rotational period. In 1884, Hall showed that the position of the elliptical orbit of Saturn's moon, [[Hyperion (moon)|Hyperion]], was [[retrograde motion|retrograding]] by about 20° per year. Hall also investigated stellar [[parallax]]es and the positions of the stars in the [[Pleiades]] star [[open cluster|cluster]].

Hall was responsible for apprenticing [[Henry S. Pritchett]] at the Naval Observatory in 1875.

===Discovery of Phobos and Deimos===
During Mars' closest approach in 1877, Hall was encouraged by [[Angeline Stickney]], his wife, to search for the Martian moons. His calculations had shown that the orbit should be very close to the planet. Hall wrote "The chance of finding a satellite appeared to be very slight, so that I might have abandoned the search had it not been for the encouragement of my wife."<ref name=Hall>Hall, Asaph, ''Observations and orbits of the satellites of Mars'', Washington: Government Printing Office, 1878 (quoted in Hall, Angelo, ''An astronomer's wife'', Baltimore: Nunn and Company, 1908, p. 112).</ref>

Asaph Hall discovered Deimos on August 12, 1877 at about 07:48 [[Coordinated Universal Time|UTC]] and Phobos on August 18, 1877, at the [[US Naval Observatory]] in [[Washington, D.C.]], at about 09:14 [[GMT]] (contemporary sources, using the pre-1925 astronomical convention that began the day at noon, give the time of discovery as 11 August 14:40 and 17 August 16:06 [[Washington mean time]] respectively).<ref>{{cite web |url=http://adsabs.harvard.edu//full/seri/Obs../0001//0000181.000.html |title=Notes: The Satellites of Mars |publisher=The Observatory, Vol. 1, No. 6 |date=September 20, 1877 |pages=181–185 |access-date=September 12, 2006}}</ref><ref>{{cite web |url=http://adsabs.harvard.edu//full/seri/AN.../0091//0000013.000.html |title=Observations of the Satellites of Mars |author=Hall, A. |publisher=Astronomische Nachrichten, Vol. 91, No. 2161 |pages=11/12–13/14 |date=October 17, 1877 |type=Signed September 21, 1877 |access-date=September 12, 2006}}</ref><ref name="Morley1989">Morley, T. A.; [http://adsabs.harvard.edu//full/seri/A+AS./0077//0000220.000.html ''A Catalogue of Ground-Based Astrometric Observations of the Martian Satellites, 1877-1982''], Astronomy and Astrophysics Supplement Series, Vol. 77, No. 2 (February 1989), pp. 209–226 (Table II, p. 220: first observation of Phobos on August 17, 1877.38498)</ref> At the time, he was deliberately searching for Martian moons. Hall had previously seen what appeared to be a Martian moon on August 10, but due to bad weather, he could not definitively identify them until later.

Hall recorded his discovery of Phobos in his notebook as follows:<ref>{{cite journal |url=http://adsabs.harvard.edu//full/seri/MNRAS/0038//0000205.000.html |journal=Monthly Notices of the Royal Astronomical Society |volume=38 |issue=4 |pages=205–209 |title=The Discovery of the Satellites of Mars |date=February 8, 1878 |bibcode=1878MNRAS..38..205H |access-date=September 12, 2006 |last1=Hall |first1=A. |doi=10.1093/mnras/38.4.190 |doi-access=free }}</ref>
[[File:Usno-telescope-equalized-1.png|thumb|left|The telescope used to discover the Martian moons]]
{{quote|
:"I repeated the examination in the early part of the night of 11th [August 1877], and again found nothing, but trying again some hours later I found a faint object on the following side and a little north of the planet. I had barely time to secure an observation of its position when fog from the River stopped the work. This was at half past two o'clock on the night of the 11th. Cloudy weather intervened for several days.
:"On 15 August the weather looking more promising, I slept at the Observatory. The sky cleared off with a thunderstorm at 11 o'clock and the search was resumed. The atmosphere however was in a very bad condition and Mars was so blazing and unsteady that nothing could be seen of the object, which we now know was at that time so near the planet as to be invisible.
:"On 16 August the object was found again on the following side of the planet, and the observations of that night showed that it was moving with the planet, and if a satellite, was near one of its elongations. Until this time I had said nothing to anyone at the Observatory of my search for a satellite of Mars, but on leaving the observatory after these observations of the 16th, at about three o'clock in the morning, I told my assistant, George Anderson, to whom I had shown the object, that I thought I had discovered a satellite of Mars. I told him also to keep quiet as I did not wish anything said until the matter was beyond doubt. He said nothing, but the thing was too good to keep and I let it out myself. On 17 August between one and two o'clock, while I was reducing my observations, Professor Newcomb came into my room to eat his lunch and I showed him my measures of the faint object near Mars which proved that it was moving with the planet.
:"On 17 August while waiting and watching for the outer moon, the inner one was discovered. The observations of the 17th and 18th put beyond doubt the character of these objects and the discovery was publicly announced by Admiral Rodgers."
|}}

[[File:The Angeline and Asaph Hall house.jpg|thumb|right|Hall's former home in the [[Georgetown, Washington, D.C.|Georgetown]] neighborhood of [[Washington, D.C.]], after enlargement. Note Angeline on front steps and two workers.]]
Hall retired from the Navy in 1891. He became a lecturer in celestial mechanics at Harvard University in 1896, and continued to teach there until 1901.