The average speed of the molecules in a gas of a given temperature.

The midpoint in the solar cycle where the amount of sunspot activity and the output of cosmic particles and solar radiation is highest.

A planet located in the inner solar system and made up mostly of rock. The rocky planets are Mercury, Venus, Earth, and Mars. This group is also known as terrestrial planets.

A galaxy in which a cosmic phenomenon, such as a supernova explosion or a gamma-ray burst, has occurred.

The process by which an atomic nucleus is transformed into another type of atomic nucleus. For example, by removing an alpha particle from the nucleus, the element radium is transformed into the eleme [..]

The beginning and the end of a sunspot cycle when only a few sunspots are usually observed, and the output of particles and radiation is normal.

A type of telescope mounting that supports the weight of the telescope and allows it to move in two directions to locate a specific target. One axis of support is vertical (called the altitude) and al [..]

An instrument that collects the infrared radiation emitted by celestial objects. There are several Earth- and space-based infrared observatories. The Infrared Telescope Facility, an Earth-bound infrar [..]

Element building that occurred in the early universe when the nuclei of primordial matter collided and fused with one another. Most of the helium in the universe was created by this process.

The Milky Way, a spiral galaxy, is the home of Earth. The Milky Way contains more than 100 billion stars and has a diameter of 100,000 light-years.