A body, such as, the Sun, that produces energy by means of nuclear reactions taking place within it: The star is held in a stable state by balancing the outward radiation pressure by the inward gravitational force.

A star is a hot, glowing sphere of gas, usually one that emits energy from nuclear reactions in its core.

A star is a luminous globe of gas, mainly hydrogen and helium, which produces its own heat and light by nuclear reactions.

Although some stars may shine for a very long time, even many billions of years, they are not eternal, and have been found to change in appearance at different stages in their forms.

One of two stars orbiting a common center of gravity: Binary stars are a pair of stars revolving around a common center of gravity, held together by their mutual gravitational interaction.

Binary stars, or a double star, is a system containing two or more stars.

In an "eclipsing binary", one star goes behind the other periodically, changing the total amount of light that we see.

An object less massive than a star, but heavier than a planet: A brown dwarf star is a theoretical "star" and does not have enough mass to ignite nuclear reactions at their centers, but shine by heat released during their contraction from a gas cloud.

Some astronomers believe that vast numbers of brown dwarf stars exist throughout the galaxy, but because of the difficulty in detecting them, none of them were discovered until 1995, when U.S. astronomers discovered a brown dwarf star in the constellation Lepus (Hare).

A star, asterism, or constellation that is close enough to the celestial pole that, depending on the latitude at which a person is observing, it never appears to set: Circumpolar stars are those that are within a circumpolar circle in which the size is determined by the viewer's latitude.

1. A pair of stars that appear close together in the sky only because they lie in the same direction from the planet Earth:, Double stars are not physically associated binary stars.
2. A system containing two or more stars: In a true double star the stars are physically close to each other in an "optical double". They lie in approximately the same direction from the planet Earth and so appear close to each other, but are actually far apart.

An older star that has converted most or all of its store of hydrogen into helium: An evolved star is a star that is nearing the end of its existence when most of its fuel has been used up.

This period of the star's duration is characterized by loss of mass from its surface in the form of a stellar wind or the ejection of gas off the surface of a star.

Many different types of stars, including our Sun, have stellar winds, however a star's wind is strongest near the end of its existence when it has consumed most of its fuel.

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.

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.

1. The result of the collapse of the remnant from a supernova explosion: The mass of a neutron star exceeds the chandrasekhar limit, but is less than that required for gravity to continue the collapse down to a black hole. 2. A very small core of a "super-dense" star: A neutron star is composed mostly of neutrons (electrically neutral subatomic particles in the baryon family).

One of a family of pulsating giant stars, with periods of less than one day: The period of particular examples does show changes, both abrupt and slow. Such RR Lyrae stars are commonly found in globular clusters.

A popular name for a meteor: A shooting star, or falling star, occurs when a meteoroid burns up while entering the Earth's atmosphere.

1. One of a group of stars that have irregular light curves, and which are believed to represent the stage in a star's evolution shortly before it appears on the main sequence: The T Tauri stars characteristically have rapid rotation and throw off much material in stellar winds.
2. One of a class of very young stars having a mass of the same order as that of the Sun: So called after a prototype identified in a bright region of gas and dust known as the Hind’s variable nebula, the T Tauri stars are characterized by erratic changes in brightness.

They represent an early stage in stellar evolution, having only recently been formed by the rapid gravitational condensation of interstellar gas and dust.

These young stars are relatively unstable, though contracting more slowly than before, and will remain in that condition until their interior temperatures become high enough to support thermonuclear reactions for energy generation.

More than 500 T Tauri stars have so far been observed. The Sun is thought to have gone through the T Tauri stage in its beginning.

agency:
start-up fund:
inventors:

"The U.S. government agency that helped invent the Internet now wants to do the same for travel to the stars."

A star whose brightness changes over time: A variable star is a star whose luminous output varies significantly with time.

Such variation may be regular; that is, eclipsing variable stars, or irregular, as with flare stars.

In addition, the variation can be intrinsic, because of changes within the star itself, or extrinsic, as the result of the interaction of one star with another.

A member of a class of stars undergoing rapid mass loss, and having peculiar spectra: Most Wolf-Rayet stars have companions in binary systems.