**Friday the 13th** is a date considered to be bad luck
in western superstition.

According to folklorists, there is no writ
ten evidence for a "Friday the 13th" superstition before the 19th century.<
sup id="cite_ref-Lachenmeyer_0-0" class="reference">[1]<
/span>^{[2<
span>]}^{[
3]} The earliest known documented reference in
English occurs in Henry Sutherland Edwards' 1869
biography of Gioachino Rossini:

**Pi Day** is an unofficial holiday commemorating the mathematical constant π (pi). Pi Day is celebrated on March 14 (or 3/14 in *month/da
y* date format), since 3, 1 and 4 are the three most sig
nificant digits of π in the decimal form. In 2009, the United States
House of Representat
ives supported the designation of Pi Day.^{[2]}

**Pi Approximation D
ay** is held on July 22 (or 22/7 in *day/month* date format), since the fraction ^{22}⁄_{7} is a common app
roximation of π.^{[3]}

**Pi Day** is an unofficial holiday commemorating the mathematical constant π (pi). Pi Day is celebrated on March 14 (or 3/14 in *month/da
y* date format), since 3, 1 and 4 are the three most sig
nificant digits of π in the decimal form. In 2009, the United States
House of Representat
ives supported the designation of Pi Day.^{[2]}

**Pi Approximation D
ay** is held on July 22 (or 22/7 in *day/month* date format), since the fraction ^{22}⁄_{7} is a common app
roximation of π.^{[3]}

**Mole Day** is an unoffic
ial holiday celebrated among chemists on October 23, between 6:02 AM an
d 6:02 PM,^{[1]}~~[2]~~^{[3]} making the date
6:02 10/23 in the American style of writing dates. The time and date are d
erived from Avogadro's number, which is a
pproximately 6.02×10^{23}, defining the number of particles (
atoms or molecules) in one mole of substance, one of the seven base SI un
its.

~~Mole Day originated in an article in ~~*The Science Teacher*
in the early 1980s.^{[4]} Inspired by this article, Maurice Oehle
r, now a retired high school chemistry teacher from Prairie du Chien, Wisconsin, founded the National Mole Day Foundation
(NMDF) on May 15, 1991.^{
[4]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

Ron Gordon, a Redwood City, Californ
ia high school teacher, created the first Square Root Day for September
9, 1981 (9/9/81). Gordon remains the holiday's publicist, sending news releases to world media outlets.^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

Ron Gordon, a Redwood City, Californ
ia high school teacher, created the first Square Root Day for September
9, 1981 (9/9/81). Gordon remains the holiday's publicist, sending news releases to world media outlets.^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

Ron Gordon, a Redwood City, Californ
ia high school teacher, created the first Square Root Day for September
9, 1981 (9/9/81). Gordon remains the holiday's publicist, sending news releases to world media outlets.^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

**Square Root Day** is an unofficial holiday
celebrated on days when both the day of the month and the month are the square
root of the last two digits of the year.^{[1]} For example, the last Squa
re Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will b
e April 4, 2016 (4/4/16). The final Square Root Day of the century will occ
ur on September 9, 2081. Square Root Days fall upon the same nine dates eac
h century.

^{[2]} Gordon's daughter set up a Facebook grou
p where people can share how they were celebrating the day.^{[3]}

Book of Revelation

Book of Daniel

Olivet discourse

Sheep and Goats

<
b>Major figures

Jesus<
br>Two Witnesses

Four Horsemen

Antichrist**Different views**

Preterism

Idealism

Historicism

Futurism**Millennial differe
nces**

Premillennialism

Amillennialism

Postmillennialism**Other events**

Chronology of Revelation

Rapture

Seven Seals

Jesus' Second Coming