Unit 1 Astronomy (honors) 24-25

Astronomical Unit (AU)

The average distance between Earth and the sun, about 150 million kilometers

Big Bang Theory

Theory of creation of Universe which includes all matter, space, time and energy by rapid expansion from an extremely small single point of extremely high density and temperature

Galaxy

a group of billions of stars held together by gravity

Hypothesis

a claim based on observed facts but not yet tested

Light Year

The distance that light travels in a year, about 9.5 trillion kilometers

Local Group

group of nearby galaxies that the Milky Way belongs to

Nebula

A large cloud of dust and gas in space

Planet

A celestial object that revolves around the sun, is a spheroid, and has cleared most of its orbit of large debris

Proxima Centauri

the next closest star to Earth (other than Sun), 4.3 light years away

Solar System

The sun and its family of orbiting planets, moons, asteroids, dwarf planets, and other debris left over from the accretion disk

Super Nova

Brilliant burst of light that follows the collapse of the core and explosion of a massive star

Virgo Supercluster

The super cluster of galaxies of which our local group is a member. Contains roughly 2000 galaxies

Universe

All observable matter, space, time, and energy

Main Sequence Star

A mass of incandescent gas, where a balance exists between the nuclear reactions pushing outward from the interior and the gravitational forces pushing inward.

Milky Way Galaxy

the spiral galaxy that contains our solar system along with billions of stars in a disk 100,000 ly across and 10,000 ly thick at the galactic bulge center

Galaxy Cluster

groupings of galaxies that are gravitationally bound and travel through space together

The Drake Equation

Calculates the probability used to estimate the number of extra-terrestrial civilizations in the solar system

Edwin Hubble

An astronomer who discovered in 1929 that galaxies are receding from us at a speed proportional to their distance (Hubble's Law) which

lead to the conclusion that our universe was expanding

Cecilia Payne-Gaposchkin

Discovered the hydrogen (H) and helium (He) rich composition of matter in space which is evidence for the Big Bang Theory

Penzias and Wilson

Scientists who discovered cosmic background radiation in 1964. One of the 3 main lines of evidence that support the Big Bang theory

Planetary Accretion

The process by which planets grow through collisions and sticking due to gravity and chance. From planetary embreyos to planetessimals to protoplanets to true planets.

Jovian Planet

Jupiter-like planets Jupiter, Saturn, Uranus and Neptune

Terrestrial Planet

Earth-like planets: Mercury, Venus, Earth, Mars

Cosmic Background Radiation

Discovered by Penzias & Wilson in 1964. Radiation left over from the early development of the universe, predicted by supporters of Big Bang over steady state model.

Kuiper Belt

A region outside the orbit of Neptune where most short-period comets are thought to originate

Dwarf Planet

A spheroid celestial body revolving around the sun, similar to a planet, but not large enough to have gravitationally cleared its orbit. Category Pluto belongs in.

Spiral galaxy

A galaxy with a bulge in the center and very distinctive spiral arms. Our Milky Way is a spiral galaxy.

Elliptical galaxy

A galaxy that has a round or elliptical outline. It contains little gas and dust, no disk or arms, and few hot, bright stars

Irregular galaxy

A galaxy that has an undefined shape; irregular galaxies have large numbers of young stars and greats amounts of gas and dust are usually found near larger galaxies.

Conservation of Angular Momentum

The law of physics stating that the total amount of angular momentum in an isolated system remains constant. Cam=mass x width x velocity. This predicts the rotational velocity changes that occur as width or mass of the rotating body are changed.

Neutron Star

The very small, very dense core of a massive star, left behind after a supernova.

Singularity

An infinitely small point which contained all the of the Universe at the beginning of time. Also refers to the single point of intense gravity left behind after a very massive star dies.

Black Hole

A point in space with a gravitational field so strong that not even light can escape. Created by the explosion of the most massive stars.

Planetary Nebula

The expanding shell of gas that is escaping a dying, Sun-like (medium mass) star.

Protostar

The piled up mass that has been pulled together by gravity at the center of a nebula. It has not yet undergone nuclear fusion.

Red giant

The stage in the life cycle of a sun-like mass star during which the star increases in size and begins to fuse helium in its core.

White Dwarf

a small, very dense star the size of earth that remains after a middle or low mass star runs out of fuel and is collapsed by gravity

Red Supergiant

The stage in the life cycle of a massive star during which the star increases in size and begins to fuse helium in its core.

gas pressure

the outward pressure exerted by gas in a star as it is heated by fusion in the core

event horizon

the location around a black hole where the escape velovity equals the speed of light; the boundary of a black hole

redshift

shift of light to a longer (redder) wavelength as the galaxy or star emitting it moves away from the observer

Andromeda Galaxy

Our closest neighboring spiral galaxy, about 2.4 million light years away

Fermi Paradox

There is a high probability that life exists elsewhere in the universe, but there is also a lack of evidence; where is everybody?

exoplanet

A planet outside of our Solar System.

Spagettification

The theory that you will become a long, thin stream of atoms, kilometers in length, but narrower than a hair wide when you get pulled into a blackhole

Steady State Theory

a theory which states that there was no beginning to the universe and that the universe does not change over time..

protoplanet

a large body of matter in orbit around the sun or a star in process of differentiation and thought to be developing into a planet.

planetessimal

Small body of matter in orbit around a star that through collisions and accretion could grow large enough and get hot enough to differentiate into layers and develop sphericity but hasn't yet

Frost line

the boundary in the solar system beyond which the gases could condense into ices; only metals and rocks could condense into solids within the frost line

Theory

well-tested claim that unifies a broad range of observations