0 is a number, the numerical digit used to represent that number in numerals. It fulfills a central role in mathematics as the additive identity of the integers, real numbers, many other algebraic structures; as a digit, 0 is used as a placeholder in place value systems. Names for the number 0 in English include zero, naught, nil, or—in contexts where at least one adjacent digit distinguishes it from the letter "O"—oh or o. Informal or slang terms for zero include zip. Ought and aught, as well as cipher, have been used historically; the word zero came into the English language via French zéro from Italian zero, Italian contraction of Venetian zevero form of Italian zefiro via ṣafira or ṣifr. In pre-Islamic time the word ṣifr had the meaning "empty". Sifr evolved to mean zero; the first known English use of zero was in 1598. The Italian mathematician Fibonacci, who grew up in North Africa and is credited with introducing the decimal system to Europe, used the term zephyrum; this became zefiro in Italian, was contracted to zero in Venetian.

The Italian word zefiro was in existence and may have influenced the spelling when transcribing Arabic ṣifr. There are different words used for the concept of zero depending on the context. For the simple notion of lacking, the words nothing and none are used. Sometimes the words nought and aught are used. Several sports have specific words such as love in tennis and duck in cricket, it is called oh in the context of telephone numbers. Slang words for zero include zip, zilch and scratch. Duck egg and goose egg are slang for zero. Ancient Egyptian numerals were base 10, they were not positional. By 1770 BC, the Egyptians had a symbol for zero in accounting texts; the symbol nfr, meaning beautiful, was used to indicate the base level in drawings of tombs and pyramids and distances were measured relative to the base line as being above or below this line. By the middle of the 2nd millennium BC, the Babylonian mathematics had a sophisticated sexagesimal positional numeral system; the lack of a positional value was indicated by a space between sexagesimal numerals.

By 300 BC, a punctuation symbol was co-opted as a placeholder in the same Babylonian system. In a tablet unearthed at Kish, the scribe Bêl-bân-aplu wrote his zeros with three hooks, rather than two slanted wedges; the Babylonian placeholder was not a true zero. Nor was it used at the end of a number, thus numbers like 2 and 120, 3 and 180, 4 and 240, looked the same because the larger numbers lacked a final sexagesimal placeholder. Only context could differentiate them; the Mesoamerican Long Count calendar developed in south-central Mexico and Central America required the use of zero as a place-holder within its vigesimal positional numeral system. Many different glyphs, including this partial quatrefoil——were used as a zero symbol for these Long Count dates, the earliest of which has a date of 36 BC. Since the eight earliest Long Count dates appear outside the Maya homeland, it is believed that the use of zero in the Americas predated the Maya and was the invention of the Olmecs. Many of the earliest Long Count dates were found within the Olmec heartland, although the Olmec civilization ended by the 4th century BC, several centuries before the earliest known Long Count dates.

Although zero became an integral part of Maya numerals, with a different, empty tortoise-like "shell shape" used for many depictions of the "zero" numeral, it is assumed to have not influenced Old World numeral systems. Quipu, a knotted cord device, used in the Inca Empire and its predecessor societies in the Andean region to record accounting and other digital data, is encoded in a base ten positional system. Zero is represented by the absence of a knot in the appropriate position; the ancient Greeks had no symbol for zero, did not use a digit placeholder for it. They seemed unsure about the status of zero as a number, they asked themselves, "How can nothing be something?", leading to philosophical and, by the medieval period, religious arguments about the nature and existence of zero and the vacuum. The paradoxes of Zeno of Elea depend in large part on the uncertain interpretation of zero. By AD 130, influenced by Hipparchus and the Babylonians, was using a symbol for zero in his work on mathematical astronomy called the Syntaxis Mathematica known as the Almagest.

The way in which it is used can be seen in his table of chords in that book. Ptolemy's zero was used within a sexagesimal numeral system otherwise using alphabetic Greek numerals; because it was used alone, not just as a placeholder, this Hellenistic zero was the earliest documented use of a numeral representing zero in the Old World. However, the positions were limited to the fractional part of a number —they were not used for the integral part of a number, indicating a concept better expressed as "none", rather than "zero" in the modern sense. In Byzantine manuscripts of Ptolemy's Almagest, the Hellenistic zero had morphed into the Greek letter omicron; the earliest use of zero in the calculation of the Julian Easter occurred before AD 311 at the first entry in a table of epacts as preserved in an Ethiopic document for the years AD 311 to 369 using a Ge'ez word for

Heaven on Earth is the second solo album by American singer Belinda Carlisle, released in 1987. The album features three singles that made the Top 10 charts in the United States, including the #1 hit and Carlisle's signature song "Heaven Is a Place on Earth", it is her most successful album to date. AllMusic's Alex Henderson gave the album four stars out of five, saying "while nothing here packs quite the punch that "How Much More," "We Got the Beat," and "Turn to You" did, such memorable songs as "Heaven Is a Place on Earth," "Should I Let You In?", "I Get Weak" show that the Angeleno still had plenty of spirit". Heaven on Earth is Carlisle's most successful studio album of her career, in terms of chart performance and copies sold; the album was certified four times Platinum in the United Kingdom. Heaven on Earth was certified Platinum in many other countries including the United States; the first single released, "Heaven Is a Place on Earth", reached the number one position throughout the world.

The second song released was "I Get Weak", written by Diane Warren. "I Get Weak" reached the number two spot in the U. S. and garnered a top 10 placing in Canada and the U. K; the third single, "Circle in the Sand", reached the top 10 in many countries, among them U. K. U. S. and Canada. From the fourth single on, the singles released from the album varied in different territories; the Cream cover "I Feel Free" was released only in the U. S. reaching #88 on the Billboard Hot 100. This was the final U. S. single from the album. In Europe, "World Without You" was released, where it reached the top 40. A fifth and final single in the U. K. was the ballad "Love Never Dies" which reached number #54. In May 2009, Heaven on Earth was re-released as a remastered two disc special edition; this special edition includes several bonus remixes and a live DVD. The inclusion of the live DVD marked the first time the concert footage filmed in Philadelphia during the 1988'Good Heavens' world tour was made available in DVD format.

It had only been available on VHS. Heaven On Earth was again re-released on August 26, 2013 in a 2CD+DVD casebook edition from Edsel Recording featuring the original album remastered, the single versions, remixes and B-sides; the DVD features the videos from the album and the concert footage filmed in Philadelphia during the 1988'Good Heavens' world tour as well as an exclusive interview with Carlisle, discussing the album. Fellow Go-Go Charlotte Caffey's group The Graces covered "Should I Let You In?" for their 1989 album Perfect View. Featuring three bonus tracks: "Heaven Is a Place on Earth", "Why", "Superstar". Belinda Carlisle – lead vocals, backing vocals Dann Huff – electric guitar John McCurry – electric guitar George Black – additional guitar Michael Landau – additional guitar Tim Pierce – additional guitar Rick Nowels – acoustic guitar, electric guitar, drum programming, backing vocals, Charles Judge – keyboards, acoustic piano, drum programming Thomas Dolby – additional keyboards Rhett Lawrence – Fairlight programming John Pierce – bass guitar Kenny Aronoff – drums Curly Smith – drums Jimmy Bralower – additional percussion Paulinho da Costa – additional percussion David Kemper – additional percussion Beth Anderson – backing vocals Charlotte Caffey – backing vocals Donna Davidson – backing vocals Donna De Lory – backing vocals Edie Lehmann – backing vocals Michelle Phillips – backing vocals Ellen Shipley – backing vocals Chynna Phillips – backing vocals Carnie Wilson – backing vocals Producer and arrangements – Rick Nowels Additional vocal production – Ellen Shipley and Robert Feist Production assistants – Matthew Freeman and Nancy Del Los Santos Production coordinator – Timothy McDaniel Recorded by Steve MacMillan Additional engineers – Stacy Baird and Robert Feist Assistant engineers – Mark DeSisto, Matthew Freeman, Clark Germain, Ron Jacobs, Ethan Jones, Brian Scheuble, Joe Schiff and Bob Vogt.

Mixing – Shelly Yakus. Mastered by Stephen Marcussen at Precision Lacquer. Art direction and design – Norman Moore Photography – Phillip Dixon Management – Danny Goldberg and Ron Stone

Royal Prussian Jagdstaffel 81 abbreviated to Jasta 81, was a "hunting group" of the Luftstreitkräfte, the air arm of the Imperial German Army during World War I. The squadron would score six or more aerial victories during July/August 1917, while serving on the Eastern Front. After switching to the Western Front, Jasta 81 would score another 35 victories from May 1918 to war's end; the unit's victories came at the expense of five killed in action, three killed in flying accidents, one injured in a flying accident, three wounded in action, three taken prisoner of war. Jasta 81 originated in Jagdflieger Ober-Ost, founded at Brest-Litovsk on 16 June 1917, it was intended for service on the Eastern Front. In August 1917, it was assigned to 8 Armee. In early May 1918, it was incorporated into Jagdgruppe 5. On 30 May 1918, it was revamped as Jasta 81. At this time, the squadron was posted to 7 Armee on the Western Front in France. On 27 June 1918, it was switched over to Jagdgruppe 4. In late September 1918, the Jasta would be assigned to 3 Armee.

Josef Wulf Herbert Knappe: 7 April 1918 - 25 August 1918 Fritz Höhn: c. 25 August 1918 - 9 September 1918 Wilhelm Pritsch: 9 September 1918 Kniaze: July 1917 Mitau: August 1917 Boncourt, France Moislains, France Séranvillers, France: August 1918 Leffincourt, France: Late September 1918 Two successive unknown locations Saint-Gerard-Maison: 26 October 1918 - November 1918 Dietrich Averes Alfons Nagler In late 1917, Jasta 81 was supplied with LFG Roland D. II fighters. BibliographyFranks, Norman. Above The Lines: The Aces and Fighter Units of the German Air Service, Naval Air Service, Flanders Marine Corps, 1914–1918. London, UK: Grub Street. ISBN 978-0-948817-73-1