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90 (Number)90 is the natural number preceded by 89 and followed by 91. In mathematics Ninety is the sums of the squares of the integers 2 to 6. Because 90 is the sum of its unitary divisors (excluding itself), it is a unitary perfect number. 90 is a pronic number. And because 90 is divisible by the sum of its digits in base 10, it is a Harshad number. But it is also a nontotient. In normal space, the interior angles of a square measure 90 degrees each. Also, in a right triangle, the angle opposing the hypotenuse measures 90 degrees, with the other two angles adding up to 90 for a total of 180 degrees. In science In astronomy, - Messier object M90, a magnitude 11.0 spiral galaxy in the constellation Virgo
- The New General Catalogue object NGC 90, a barred spiral galaxy in the constellation Andromeda
- The Saros number of the solar eclipse series which began on 134 BC September 28 and ended on 1345 March 4. The duration of Saros series 90 was 1478.4 years, and it contained 83 solar eclipses.
- The Saros number of the lunar eclipse series which began on 150 June 27 and ended on 1430 August 4. The duration of Saros series 90 was 1280.1 years, and it contained 72 lunar eclipses.
In other fields Ninety is:
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