April 9 is the 99th day of the year, there are 266 days left
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Today is also Prickle-Prickle, Discord 26, 3184 YOLD
(for the discordians amongst us)

Today's number is 9

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9 is the largest single digit integer
9 is the square of a prime and is the second lowest such square

"Casting out nines" is a quick way of testing the calculations of sums, differences, products, and quotients of integers. It was known as long ago as the 12th Century. It is also the basis of a lot of "magic" tricks and puzzles. There used to be some based on the rotary phone dial too. Essentially, They are modulo 9 math.

A number is divisible by 9 if its digital root is 9. A number's digital root is the sum of its digits. If such sum is greater than one digit, then those digits are also summed, etc. Thus the digital root of 18 is 9 (8+1), and the digital root of 456 is 6 (4+5+6 = 15 and 1+5 = 6)

Now the fun:
1/9 = 0.11 followed by an infinite string of 1s
2/9 = 2 x 0.11 to infinity = 0.22 followed by an infinite string of 2s
3/9, of course, is 0.33 fol;lowed by an infinite string of 3s, etc.
This brings us to
9/9 = 0.99 followed by an infinite string of 9s, which is also 1. Back in the stoneage, a test of calculators and computers was to perform the operation (1/9)x9 and see if it returned 1 or 0.9999999 etc.

Conversely:
123456789 x 9 = 111,111,111
123456789 x 18 = 222,222,222 (because 18 = 2 x 9)
etc up to
123456789 x 72 = 888,888,888 (9 x 8 ) and
123456789 x 81 = 999,999,999 (9 x 9)

9 is the number of lives a domestic cat has
9 is the Jersey number worn by the inimitable Ted Williams.
9 is Fluorine.
9 is Organic: Five-digit produce PLU codes that begin with 9 are organic.
A 9 sided polygon is a nonagon, aka an enneagon
There are 9 justices on the US Supreme Courtallowfullscreen>

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Title 9 of the US Code is Arbitration

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9 BCE
was the Year of the Consulship of Drusus and Crispinus
Nero Claudius Drusus died and Emperor Ping of Han was born.

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9 CE
was the Year of the Consulship of Sabinus and Camerinus
The Rhine river was established as the boundary between the Latin- and German-speaking worlds, following the defeat of the Roman army, under the command of Varus, at the Battle of the Teutoburg Forest. (Varus again)
Italy adopted the Lex Papia Poppaea outlawing celibacy and childless relationships, unlike later under the popes, who favored celibacy, though still abhorring childless relationships. (Confused much?)
In China, Wang Mang founded the Xin dynasty, which lasted 16 years
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On this day in:
An enormous number of battles were staerted, fought or concluded on Aprol 9, so I'll skip all but one

1288 -- Tran forces whupped Yuan forces at Bach Dang stopping Mongol incursions into Viet Nam
1585 -- Sir Walter Raleigh left England for Roanoke Island
1609 -- Philip III decreed the "Expulsion of the Moriscos"
1682 -- de La Salle discovered the mouth of the Mississippi and claimed it for France
1860 -- Edouard-Leon Scott de Martinville madethe oldest known recording of a human voice
1939 -- Marian Anderson sang at the Lincoln Memorial
1945 -- The US Atomic Energy Commission was formed
1947 -- The first interracial Freedom Ride began
1952 -- The Bolivian National Revolution overthrew Hugo Ballivian's self-coup
1957 -- The Suez Canal was re-opened to shipping
1961 -- The Pacific Electric Railway in L.A. shut down
1967 -- The first Boeing 737 made its maiden flight
1991 -- Georgia declared independence from the USSR

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Born this day in:

1770 -- Thomas Johann Seebeck, physicist
1794 -- Theobald Boehm, falutist and composer
1821 -- Charles Baudelaire, poet
1830 -- Eadweard Muybridge, photographer
1835 -- Leopold II of Belgium, notorious asshole
1895 -- Mance Lipscomb, singer, songwriter and guitarist
1898 -- Paul Robeson, singer, actor, activist, commie
1904 -- Sharkey Bonano, trumpet player, singer, and bandleader
1919 -- J. Presper Eckert, engineer who invented the ENIAC
1921 -- Mary Jackson, mathematician and aerospace engineer
1928 -- Tom Lehrer, mathematician, pianist, singer and songwriter
1932 -- Carl Perkins, singer, songwriter and guitarist
1936 -- Valerie Solanas, feminist author, would be assassin
1945 -- Steve Gadd, drummer

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Died this day in:

1553 -- Francois Rabelais, writer and physician famous for fart jokes
1626 -- Francis Bacon, empiricist, philosopher, jurist, politician
1768 -- Sarah Fielding, author, wrote first novel for children
1953 -- Hans Reichenbach, vienna circle philosopher
1959 -- Frank Lloyd Wright, architect
1963 -- Eddie Edwards, trombonist
1976 -- Phil Ochs, guitarist, songwriter, and singer
1988 -- Brook Benton, singer and songwriter
1988 -- Dave Prater, singer
2007 -- Dorrit Hoffleit, research astronomer

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Holidays, Holy Days, Festivals, Feast Days and such:

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Marian Anderson

Mance Lipscomb

Paul Robeson

Sharkey Bonano

Tom Lehrer

Carl Perkins

Steve Gadd

Phil Ochs

Brook Benton

Dave Prater

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picture is Eleanor Roosevelt and Marian Anderson in Japan, 05/22/1953; created by FDR

It's an open thread, so do your thing