Stars, Galaxies and The Universe

Absolute magnitude

The brightness of a star as seen from a distance of 10 parsecs. Absolute magnitude. Absolute magnitude is a measure of how bright a star or celestial object appears from a standard distance of 10 parsecs about 32.6 light years.

Apparent magnitude

The brightness of a star as seen from Earth. Apparent magnitude. Apparent magnitude is a measure of how bright a star or celestial object appears from Earth.

Big bang theory

States that the universe began with a huge explosion 13.8 billion years ago. Big Bang Theory. The Big Bang Theory explains that the universe started from an extremely hot and dense point and has been expanding ever since.

Black hole

A region in space with gravity so strong that no matter or light can escape it. Black hole. A black hole is an invisible spot in space where gravity pulls so hard that nothing can get out, not even light.

Galaxy

A massive system of stars, gases, and dust held together by gravity. Galaxy. A galaxy is a huge collection of stars, planets, and other matter bound together by gravity.

Light year

The distance light travels in a year 9.5 trillion km. light year. A light year is the distance that light travels in one year.

Main sequence

The distinct diagonal band on an H-R diagram that includes 90 of all stars. Main sequence. Main sequence stars are those that are in a stable phase of their life, fusing hydrogen into helium in their cores.

Nebula

A huge cloud of gas and dust in space, where new stars form. Nebula. A nebula is a giant cosmic cloud where stars are born.

Neutron star

A dense core composed mainly of neutrons, left behind after a supernova explosion. Neutron star. A neutron star is an incredibly dense and compact object formed from the remnants of a massive star after it explodes in a supernova.

Nuclear fusion in the sun

The process by which hydrogen atoms join together to form helium, inside the sun nuclear fusion in the sun. Nuclear fusion in the sun is the reaction that powers the sun, fusing hydrogen atoms into helium and releasing energy.

Parallax

The apparent change in position of an object when viewed from different places. Parallax. In simple terms, parallax is the way an object's position seems to change when you look at it from different locations, which is often used in astronomy to measure distances to stars.

Quasar

The very bright center of a distant galaxy. Quasar. A quasar is a massive, extremely bright object powered by a supermassive black hole at the center of a distant galaxy.

Supernova

The bright explosion of a dying super giant star. Supernova. A supernova is a powerful explosion of a star at the end of its life, releasing massive amounts of energy and light.

White dwarf

The hot dense core of a star left behind when its outer layers have escaped into space. White dwarf. A white dwarf is a small, dense star that forms when a star like our Sun uses up its nuclear fuel and sheds its outer layers.