Astronomy and related astronomical terms

A region in the sun's photosphere brighter than its surroundings, related to sunspots and to the sun's magnetic field: Such areas of faculae are at a higher temperature than the surrounding areas.

A popular term for a meteor; meteor burst: Jack and Jill decided to watch the stars during the clear, cloudless night, and suddenly saw a falling star, or shooting star, which was a bright streak of light in the sky.

The point at which the sun, traveling from south to north on the ecliptic, crosses the celestial equator: The First Point of Aries occurs on March equinox.

The First Point of Aries is identical to the vernal equinox.

A sudden, transitory burst of activity in the sun's atmosphere involving the release of radiation and high-energy particles: The origin of flares is uncertain, although they seem to be related to areas of high magnetic fields.

A star whose brightness can increase by as much as two to 100 times in a matter of minutes, then return to normal: The sudden brightness of a flare star, as a faint red dwarf, fades away quickly after amounting to many magnitudes of bright intensity.

A flying object whose nature is unknown: In his astronomy class, Alfred learned about flying saucers as being a disk-shaped unidentified object, or UFO, or anything considered to have extraterrestrial origins.

The breakup of a gas cloud into discrete regions: Fragmentation results from the gravitational collapse of denser regions in the gas or inhomogeneities (something that is not homogeneous or uniform).

The number of repetitions or cycles per unit time of a complete waveform, expressed in Hertz (Hz): Shortwaves pass the point at high frequencies, and longer ones at low frequencies.

The study of the Milky Way galaxy and all its contents: The field of galactic astronomy is in contrast to "extragalactic astronomy", which is the study of everything outside our solar system, including all other galaxies.

A congregation, or large grouping, of millions or billions of stars: A galaxy is held together by gravity or gravitational attraction and also known as an "island universe".

A galaxy can also be described as a collection of dust, gas, and stars measuring thousands of parsecs across.

A "parsec" comes from PARallax + SECond which is a unit of distance between stars. One parsec is about 3 1/4 light years.

The four largest moons, or satellites, of Jupiter, specifically Ganymede, Callisto, Io, and Europa. The Galilean satellites were first observed by Galileo Galilei.

An Italian astronomer (1564-1642) and physicist: Galileo Galilei is associated with many of the important advances in science in the late Middle Ages.

Galileo made major investigations in the fields of mechanics, including experiments on acceleration, friction, inertia, and falling bodies.

He is credited with improving the telescope and pioneered its use for astronomical observations, discovdering mountains on the moon, many new stars, the four satellites of Jupiter, and the composition of the Milky Way.

He also supported the theories of Copernicus concerning the motions of the planets.

Electromagnetic radiation with wavelengths shorter than those of X-rays: Gamma radiation is given off by any type of origin, but particularly by a part of the electromagnetic spectrum with a wavelength no more than 1 × 10–11 metres

One of the planets in our solar system that consist of hydrogen and helium: The best examples of gas giants are the four planets, Jupiter, Saturn, Uranus, and Neptune.

A prominent zodiacal constellation in the northern hemisphere: Gemini is represented as the twins Castor and Pollux.

Its brightest star is Pollux; Castor is a system of six stars.

The sun passes through Gemini from late June to late July. Each December, the Geminid meteors radiate from Gemini.