General astronomy

General astronomy

Contributors in General astronomy

General astronomy

A cloud of interstellar gas and dust that appears bright due to its reflection or scattering of starlight. The light from a reflection nebula has the same spectral lines as the starlight it reflects, ...

mean solar day

Astronomy; General astronomy

The average length of an apparent solar day or the interval between successive transits of the mean sun. The apparent solar day is not constant in length due to the changing value of the equation of ...

open cluster

Astronomy; General astronomy

A group of stars formed together in the spiral arms of a galaxy. Open clusters are usually irregular in shape and contain a few dozen to several hundred relatively young stars in a volume up to 50 ...

magnetogram

Astronomy; General astronomy

A map of the magnetic field across the Sun's photosphere, measured by the Zeeman splitting of Fraunhofer lines. Daily magnetograms are produced by a number of observatories around the world. Those ...

open universe

Astronomy; General astronomy

A universe which expands forever with an infinite lifetime. A Friedmann universe with a density less than the critical density is an open universe. It is not yet known whether our Universe is of this ...

primary cosmic ray

Astronomy; General astronomy

An atomic particle moving at a speed close to that of light and with extremely high energy (108–1020 eV). On collision with atoms in the Earth's atmosphere, a primary cosmic ray produces showers of ...