The range of frequencies or wavelengths to which a detector of electromagnetic radiation is sensitive.

A unit in which pressure is measured, particularly planetary atmospheric pressure. One bar is close to the average pressure of the Earth’s atmosphere at sea level, and is equal to 105 pascals newtons per square metre. Atmospheric pressures are often quoted in millibars 1,000 mbar = 1 bar.

Medieval Jewish astronomer and mathematician who lived in Barcelona, in Spain. In his Treatise on Mensuration and Calculations he introduced Europe to the Arabic mathematical discipline of trigonometry. In Latin translation, this book served as the main source material for the later work of Leonardo Fibonacci of Pisa. Bar Hiyya’s book The Shape of the Earth contains a roughly correct estimate of the distance from the Earth to the Moon.

A giant star with a spectral type in the range G2 to K4 that has in its spectrum unusually strong absorption lines of the element barium.

A diverging lens used in conjunction with a telescope eyepiece. The Barlow lens increases the effective focal length of the telescope, which causes the eyepiece to yield a higher magnification.

The galaxy NGC 6822 in Sagittarius.

A faint ring of hot gas, forming an ellipse 14° by 10° in the constellation of Orion. It is thought to be the result of radiation pressure from the hot stars in the region of Orion’s belt and sword acting on interstellar material.

A ninth magnitude star in the constellation Ophiuchus that has the largest known proper motion of any star, a fact discovered by the American astronomer E. E. Barnard in 1916. Its position in the sky changes by 10.3 arc seconds each year as it moves through space relative to the Sun. It is the third-nearest star to the Sun at a distance of 5.88 light years. Possible wobbles in the motion of Barnard’s star have been interpreted as indicating the presence of unseen planets, but this suspicion has not been confirmed.

A common type of spiral galaxy in which the spiral arms apparently emanate from each end of a bright central bar of stars.

distortion

Arizona meteorite crater.

A 46-kilogram stony meteorite that fell near the village of Barwell, Leicestershire, UK, in 1965. Though it broke up, it was the largest stony meteorite known to have fallen in the UK.

The centre of mass of a system of objects moving under the influence of their mutual gravity. The barycentre of the solar system, for example, is constantly moving as the relative positions of the planets particularly the major ones change. It lies about a million kilometres from the centre of the Sun.

Coordinates defining the position of a body in the solar system referred to the barycentre as origin.

dynamical time.