Earth Science 25 BJU 5th ed

Constellation

A group of stars that form a pattern or shape in the sky.

Apparent magnitude

How bright a star looks from Earth.

Absolute magnitude

How bright a star actually is, from a standard distance.

Cepheid variable

A star that gets brighter and dimmer in a regular pattern.

Light-year (ly)

The distance light travels in one year (about 9.5 trillion km).

Parsec (pc)

A unit for measuring space distances, equal to about 3.26 light-years.

Parallax

The way a star’s position seems to change when viewed from different places, used to measure distance.

Supergiant

A huge, very bright star that is near the end of its life.

Hertzsprung-Russell diagram

A chart that shows stars’ brightness and temperature to help understand their life stages.

Main sequence

The main stage of a star’s life when it burns hydrogen into helium.

Red giant

A star that has expanded and cooled after using up its hydrogen fuel.

White dwarf

A small, hot star left over after a red giant loses its outer layers.

Nova

A sudden burst of brightness from a star, caused by a surface explosion.

Supernova

A powerful explosion that happens when a massive star dies.

Neutron star

A very small, dense star made mostly of neutrons, formed after a supernova.

Black hole

An area in space with gravity so strong that nothing, not even light, can escape.

Nebula

A large cloud of gas and dust in space where stars can form.

Binary star

Two stars that orbit around each other.

Star cluster

A group of stars that are close together and move as a group.

Galaxy

A huge system of stars, gas, and dust held together by gravity.

Quasar

A very bright object far away, powered by a supermassive black hole.

Cosmology

The study of the universe as a whole—how it began and how it changes.

Cosmogony

The study of how the universe or parts of it (like stars or planets) first formed.

Cosmological red shift

The stretching of light from distant galaxies, showing the universe is expanding.

Cosmic microwave background radiation (CMBR)

Faint leftover heat from the early universe, a clue to its beginning.

Big Bang theory

The idea that the universe began from a tiny, hot, dense point and has been expanding ever since.

Stellar evolution

The process of how stars form, live, and die.

Dark matter

A mysterious type of matter that we can’t see but know is there because of its gravity.

Asterisms

A recognizable pattern of stars that is part of a constellation or made from stars in multiple constellations (e.g., the Big Dipper).

Constellations

Officially recognized areas of the sky with specific star patterns, used to map the heavens (e.g., Orion, Ursa Major).

Absolute Magnitude

The actual brightness of a star as it would appear if it were placed 10 parsecs (32.6 light-years) from Earth.

Parsecs

A unit of distance used in astronomy; 1 parsec is approximately 3.26 light-years.

Supergiants

Extremely large and bright stars with much greater size and mass than the Sun, usually nearing the end of their life cycle.

Hertzsprung-Russell Diagram

A graph that shows the relationship between a star’s brightness (luminosity) and its temperature, helping scientists classify stars.

Main Sequence

The band of stars on the Hertzsprung-Russell diagram where most stars, including the Sun, are found while they are actively fusing hydrogen into helium.

Supernova

A powerful explosion that occurs when a massive star runs out of fuel and collapses, often leaving behind a neutron star or black hole.

Black Hole

A region of space with gravity so strong that nothing, not even light, can escape from it; formed from the collapse of very massive stars.

White-hole cosmology

A theory that suggests the universe may have started from something like a white hole, which is the opposite of a black hole. Instead of pulling things in, a white hole pushes matter and energy out, possibly creating space, stars, and planets. Some people who believe in a young Earth use this idea to explain how distant stars could be seen so soon after the universe began.

Light created in transit

A creationist idea that says God created light already on its way to Earth from stars, even if the stars are very far away. This means we can see their light even if the universe is only a few thousand years old.

Stellar aging

The process of a star getting older and changing over time. Just like people, stars go through life stages, starting as young stars and eventually running out of fuel.

The Dasha solution

A creationist model that says Earth was made in six days (like in the Bible), but the rest of the universe aged faster because of gravity and time differences. It uses science ideas like time dilation to explain how we can see stars that are really far away in a young universe.

Protostars

Baby stars that are just beginning to form. They are made when gas and dust in space are pulled together by gravity. If a this star gets hot and dense enough, it can become a real star.

Stellar evolution

The full life cycle of a star. This includes how it forms, changes as it uses up its fuel, and eventually dies—either by fading out, becoming a white dwarf, or exploding as a supernova.