astronomy

Declination

The angular distance in degrees of an object north or south of the celestial equator.

Right Ascension (R.A)

The position of an object that is comparable to longitude on Earth; measured in units of hours and minutes.

Zenith

The highest point in the sky at any particular time and location.

Look Back Time

The fact that we see objects as they were in the past when we look out into space.

Milky Way Galaxy

Our star, the Sun, is one of 100 billion stars that form the…

Constellations

Patterns we create in the sky to symbolize important stories and to locate things in the sky.

Degree

A unit of angular measure equal to 1/360th of a full circle.

Astronomical Unit (AU)

The average distance between Earth and Sun

Big Bang

All evidence indicates that the universe started 13.75 billion years ago in the…

Planet

A large object that directly orbits a star and is massive enough to both become a sphere and to mostly clear out the debris in its orbit.

Supercluster

An enormous clumping of thousands of galaxies.

Local Group

Our galaxy is a part of the _ of about 24 galaxies.

Solar System

All the stuff going around our Sun including our own planet and the Sun.

Universe

The sum total of all space, time, matter, energy, puppy dogs, etc.

Observable Universe

All the stuff that we can see that is closer than 13.75 billion ly away.

Azimuth

The position along the horizon that one should face to see a particular object in the sky.

Altitude

The angular distance above the horizon of a particular object in the sky.

Comet

A small object made mostly of ice and a little rock that is orbiting a star.

Asteroid

A small object made mostly of rock, and maybe some ice, that is orbiting a star.

Rotation

Most objects in the universe spin. This is called…

Arcminute

One sixtieth of a degree. (1/60)

Arcsecond

One sixtieth of an arcminute or 1/3600 of a degree.

Axis Tilt

Earth's axis is 23.5 degrees off from being perpendicular to our orbit. We call this…

Summer Solstice

That time when Earth's northern pole is tipped the most toward the Sun.

Solstice

This literally translates as "Sun stop" because the north-south motion of the Sun stops and goes in the other direction at this time.

Vernal Equinox

The Northern Hemisphere time when the Sun crosses the celestial equator heading northward.

Ecliptic

The apparent path of the Sun against the background stars over the course of a year.

Zodiac

The constellations that fall along the ecliptic. It translates from Greek as "circle of animals."

Phases of the Moon

The shape of the illuminated portion of the Moon that we see changes, this is the…

Synchronous Rotation

The same side of the Moon always faces Earth (ignoring a tiny wobble) this is called…

Lunar Eclipse

When Earth's shadow falls on the Moon we call it a… (Might be total or partial.)

Solar Eclipse (not total)

This happens when the Sun-Moon-Earth are in a direct line (in that order.) The solar eclipse is only total in one spot and is partial or no eclipse else on that side of Earth.

Umbra

The darkest part of an object's shadow, i.e., where the entire light source is blocked.

Penumbra

That part of an object's shadow where only part of the Sun is blocked from view.

Retrograde Motion

Ancient civilizations had troubles explaining the odd motion of the planets, especially…

Geocentric

It is difficult to explain the motions of the heavens for a universe that is believed to be..

Stellar Parallax

The main problem with accepting that Earth orbited the Sun was the inability to detect any shifting in the stars as we orbit the Sun. This apparent shifting of the stars is called…

Heliocentric

Our modern understanding has us at a random spot in our galaxy in a solar system that is…

Total Lunar Eclipse

This happens when the moon is completely inside the darkest part of Earth's shadow.

Hypothesis

An educated guess on the part of a scientist as she prepares to study some phenomena.

Aristotle

The Greek philosopher who defined our view of the natural world for nearly 2k years.

Galileo

The "Father of Modern Science" who defined what we now know as "the scientific method."

Kepler

He figured out the motion of the planet including that they travel on elliptical paths.
He abandoned the idea of perfect circles and solved the riddle of planetary orbits.

Period

The time required for an object to complete one orbit around the Sun is the…

Occam's Razor

The philosophy that simple theories are usually better than complicated ones.

Astrology

An ancient religion now known to be completely unfounded on anything factual.

Parallax

Small "shifting" of relatively nearby objects compared to distant ones when viewed from different places.

Newton

He provided the understanding of the "cause" of planetary motion.

Newton's Laws of Motion

Three laws that describe the motion of pretty much any object on Earth or in space.

Kepler's Laws

Three laws that describe the motion of planets around a star.

Theory

Typically, only well accepted ideas with vast amounts of testing and data become…

Semimajor Axis

This is used for ellipses like "radius" is used for circles.

Paradigm

A generally accepted pattern of thought and/or model is known as a…

Light Gatherin Ability

This is a measure of how much light a telescope can collect. It is more important than mgnification for most aastronomical uses.

Reflecting telescope

Almost all research telescopes use a mirror to gather light, this type of telescope is a…

Universal Law of Gravitation

This idea explained a lot about falling objects, orbiting planets, returning comets, etc.

Ptolemy

The Greek philosopher who defined a complicated model of the geocentric universe.

Copernicus

He wrote 'De Reolutionibus Orbium Coelestium,' which describes a heliocentric solar system. Unfortunately, it was only slightly better than that by C. Ptolemy.

Sun

The larest object in the solar system. It dominates all aspects of the solar system.

Terrestrial Planets

The class of planets that includes Earth, Mercury, Venus and Mars.

Jovian Planets

The class of planets that includes Jupiter, Saturn, Uranus and Neptune.

Asteroid

A small orbiting object that is comprised of metal and rock.

Asteroid Belt

The collection of debris that is located between the orbits of Mars and Jupiter.

Kuiper Belt

A donut shaped ring of icy bodies past Neptune that contains many dwarf planets.

Oort Cloud

A vast and very distant halo of small icy bodies that surrounds our solar system.

Conservation of Energy

Energy can be converted between forms but cannot be created or destroyed.

Conservation of Angular Momentum

If there are no external forces, spinning objects must obey the law of…

Solar Nebula

Our star and the solar system very likely formed from a large gas cloud called the…

Nebular Theory

The idea that stars and their planets formed from the collapse of large gas clouds.
As we learn more from newly discovered extrasolar systems, we may need to modify it.

Condensation

At very low temperatures some atoms and molecules will start to stick together.

Accretion

The process by which larger particles start to stick together, mostly by gravity.

Frost Line

As the solar system formed, icy stuff and gases collected further from the Sun, meanwhile rocky and metallic particles accreted closer to the Sun. The dividing line is the…

Heavy Bombardment

Early in the history of our solar system there were lots of small objects pounding into all the planets and moons, leaving a lot of craters.

Giant Impact

Earth's Moon was likely caused by a XXXXX between Earth and a huge plantesimal.

Radiometric Dating

Measurements of the abundance of different radioactive isotopes to determine age.

Half-Life

If you start with a kilogram of radioactive material after one you will only have 500 grams left. After yet another you will only have 250 grams left.

Helium

When our Solar System formed the vast majority of the material was hydrogen and…

Dwarf Planet

Sadly for kids everywhere, scientists have demoted Pluto to being only a…

Differentiation

Higher density material sinks to a planet's center and less dense materials float to the top.

Core

The center of a planet's structure where the highest density materials reside.

Mantle

A region inside of a planet that contains medium density rocks bearing silicon and oxygen.

Lithosphere

A rigid region of rock that "floats" on the softer molten (or core) rock below.

Crust

A very thin layer of rock that is the outer most layer of all terrestrial planets.

Impact Cratering

When asteroids or other objects strike a planet or moon the surface is changed through…

Volcanism

Molten rock from a planet's inner layers coming to the surface.

Plate Tectonics

When a planete's lithosphere cracks and moves about causing surface changes.

Erosion

The reshaping of a planet's surface by wind, water and ice.

Electomagnetic Spectrum

Photons of any wavelength from infared through gamma rays.

Ozone (O3)

Located in the middle of the stratosphere this layer of our atmosphere protects us from ultraviolet radiation.

Thermal Radiation

The temperature of an object can be measured by observing the most intense wavelength.

Greenhouse Effect

Different wavelengths of light can pass through an atmosphere or are blocked. This causes a planet to warm up.

Global Warming

The addition of anthropogenic CO2 and other gases is causing climate change on Earth.

Lunar Maria

Parts of the Moon's surface have been flooded with lava forming smooth "seas."

A Magnetic Field

Spinning Planets with fluid electrically conductive cores form…

Convection

The movement of fluids (liquids and gases) caused by uneven heating.

Outgassing

The release of gases mostly CO2 especially from a planet's volcanoes.

CO2 Cycle

Our planet regulates its temperature over time by this process.

Metallic Hydrogen

The magnetic fields of Jupiter and Saturn are generated by the electrically conductive..

Rings

All four gas giants have of countless icy particles surrounding them.

Moonlets

Planetary rings are not ephemeral but are constantly being renewed, the source seems to be…