One of the components of the solar corona caused by light scattered from dust particles in the vicinity of the Sun. The F stands for Fraunhofer: the spectrum of the F corona is that of the Sun, including Fraunhofer lines. See also: zodiacal light.

A star of spectral type F. F stars on the main sequence have surface temperatures in the range 6,000-7,400 K. Their spectra are characterized by strong absorption lines of ionized calcium the H and K lines, which are stronger than the hydrogen lines. There are also many medium-strength absorption lines due to iron and other heavier elements. Procyon and Polaris are examples of F stars.

Abbreviation for focal ratio.

A subclass of the C-type asteroids, distinguished by weak or no ultraviolet absorption in their spectra.

An alternative expression for oscillator strength.

An optical instrument in which the phenomenon of interference produced by multiple reflection between two precisely parallel glass plates is exploited to achieve a high degree of resolution in the study of spectra. The pair of plates, with an adjustable air space between them, is called an etalon. In transmission, the illuminated field of view appears as a series of bright concentric rings on a dark background, the angular diameters of which depend on the spacing of the etalon and the wavelength of the light. Inserted in front of the grating or prism in a spectrograph, it provides a means of revealing fine structure in a spectrum that could not be detected by the use of a diffraction grating alone.

A bright region of the Sun’s photosphere. The appearance of faculae is linked to the subsequent emergence of sunspots in the same vicinity and solar activity in general.

A bright spot on a planetary surface, particularly on Ganymede.

A meteorite recovered after it has been observed to fall.

A popular North American term for a meteor.

A visual representation of an image in which the colours are not those that would be seen by a normal human eye in natural conditions. In astronomy, false colour is used to enhance the contrast of an image and so bring out details that would otherwise be difficult to see. False colour is also used to make visual representations of observations made in wavelength regions other than visible light.

An asterism in the shape of a cross in the southern constellations Carina and Vela, made up of the stars ε Epsilon and ι Iota Carinae and δ Delta and κ Kappa Velorum. The name arises because of the possibility of confusion with the nearby constellation Crux.

A NASA satellite for ultraviolet astronomy scheduled for launch in 1998.

A European Space Agency project for an orbiting observatory operating in the wavelength band from 100 microns to 1 mm. Launch is scheduled for 2007 and the operating lifetime is intended to be six years. The main scientific objectives are the study of the interstellar medium, star formation, the cosmic background radiation and the composition of comets.

The rotation of the plane of polarization of radio synchrotron radiation. The effect is caused by the presence of a magnetic field and free electrons in the region through which the radiation passes. See also: rotation measure.