Quadrature (astronomy)

As quadrature is called in astronomy the aspect in which a celestial body by another has a geocentric angular distance of 90 degrees. If the other heavenly bodies not named, it is usually the quadrature to the sun, ie of the heavenly bodies has just an elongation of 90 degrees.

The moon is in the first and last quarter with the sun in quadrature. If an upper Planet in quadrature to the sun, as he shows himself not fully lit, but at a certain phase angle. This is the angle, appear seen under the sun from the earth and planets. The phase angle is at a maximum at quadrature. Instead of the term quadrature is therefore often spoken of the greatest phase. However, this is only noticeable, at Mars on the planetary disk. He then has a shape as the moon phase three to four days before and after the full moon.

The inferior planets Mercury and Venus can never be in quadrature, as their greatest elongation is less than 90 degrees.

Outside the solar system, it is referred to as quadrature, when it emerges from a double star or Exoplanetensystem the 90 degree angle between the observer on the earth and the companion star, ie measured from the main star of.