Astronomy: Glossary


a rocky object in space that can be a few feet wide to several hundred miles wide. Most Solar System asteroids orbit in a belt between Mars and Jupiter
a prefix that means "star" in the Greek language
a person who travels in space. The word, 'astronaut' comes from the Greek words meaning "space sailor."
a scientist who makes observations and studies planets, stars, galaxies any anything else in space
astronomical unit
a unit of length used by astronomers. One astronomical unit equals the distance from Earth to the Sun: 93 million miles
the study of everything that is or was in space beyond the Earth's atmosphere. Astronomy is the oldest science, dating back thousands of years to when people noticed objects in the sky overhead and watched how they moved
a branch of astronomy. It is the investigation of objects in space by remote sensing from Earth or its vicinity
the layer of gases surrounding the earth that has gravity strong enough to prevent the gases from escaping into space
a glow over the polar regions caused by the interaction between Earth's magnetic field and charged particles from the Sun


Big Bang Theory
a theory that says that the universe began with the rapid expansion of all space, time, and matter from a single point
black dwarf
the remains of a white dwarf after it cools
black hole
super dense invisible objects in outer space that form when a massive star collapses from its own gravity. Black holes have such an enormous amount of gravity that nothing, not even light, ca escape from them


celestial body
an object that is located in outer space
a small frozen mass of gas, dust, and ice. Comets revolve around the Sun or pass through the Solar System in elliptical orbit
often the pilot. Commanders are responsible for the vehicle, the crew, mission success, and safety
groups of stars in that people have imagined to represent various objects or mythical beings
the Russian term for an astronaut
a hole formed by a meteorite hitting the surface of a planet or a moon dark matter


dwarf planet
a space body too small to be called a planet


shaped like an egg, but with equal ends
embryonic star cloud (another name for nebula)
huge cocoons of dust grains, gas, and molecules that are the birthplace of stars


a huge collection of stars, nebulae, star clusters, and dust and gas that measures many light years across. A galaxy's shape can be elliptical, spiral, or irregular
Galileo Galilei
(1564-1642) - Italian mathematician, astronomer, and physicist. In 1609, Galileo was the first person to use a telescope to observe the skies. Galileo discovered the rings of Saturn, was the first person to see the four major moons of Jupiter, observed the phases of Venus, and studied sunspots
the attractive force of a body. The larger or more dense the body, the greater the gravitational force


1,000 meters. A kilometer equals 0.6214 miles


light year
units used t o measure distance in space. One light- year is the distance light can travel in one year, which is about 6,000,000,000,000 (6 trillion) miles, or 9,500,000,000,000 kilometers


a meteoroid that enters the Earth's atmosphere, heats up, and looks like a brief streak of fire in the sky
a part of a meteor that does not burn up when it enters the Earth's atmosphere but falls to the Earth's surface
a piece of stone or metal that travels in space around the sun
meteor shower
what you might see when Earth passes through the tail of a very old comet. During a shower you might see between 30 - 80 meteors an hour. Two well-known major showers are the Perseid shower, which peaks on August 12, and the Geminid shower which peaks on December 13
Milky Way
the galaxy that contains the solar system
mission specialist
astronauts in charge of on-board operations. They release satellites into space, operate scientific or engineering experiments, repair satellites and operate equipment in the Shuttle's payload bay
one of a planet's natural satellites, generally no smaller than ten miles in diameter. There are more than fifty known moons in the Solar System, including Earth's


the National Aeronautics and Space Administration. NASA is in charge of all space programs for the United States
directing the course of a ship or other craft
(another name for embryonic star cloud) a cloud of dust and gas in space in which a star is born
neutron star
a rapidly spinning, extremely dense star composed of mainly neutrons (parts of an atom).. Neutron stars are the leftovers of a supernova. They are only about 10 miles across, but are very dense
(not emitting light or visible) material that cannot be seen in the sky. Dark matter is one of the most mysterious things in the universe. Scientists think that dark matter occurs everywhere but they don't yet know exactly what it is made of


optical telescope
a telescope that uses mirrors to reflect an image to the observer
the path followed by an object in space as it moves moves around another object


in space flight, the passengers, crew, instruments, or equipment carried by a spacecraft
payload specialist
professionals from life sciences or physical sciences fields. They can also be skilled technicians who are trained to operate special equipment on the mission
controls and operates the shuttle
a spherical object that orbits a central star and reflects the suns light. It's diameter can vary but is usually between 1,000 and 100,000 miles
Pulsars are thought to be rapidly rotating neutron stars with very strong magnetic fields. Bursts of energy are detected on earth from a pulsar at spaced intervals of several seconds or less


Quasars are not stars. They are galaxies traveling away from us at tremendous speeds


radio telescope
a telescope that studies planets, star, galaxies and other astronomical objects by using the radio waves they emit. These waves are longer than light waves and need very large antennas or arrays of antennas to capture them
radio wave
electromagnetic radiation. Other types of electromagnetic radiation are heat, light, and X-rays
red giant
a star that becomes cooler, swells and glows with a red color. This happens after a medium-sized star has used up all its energy and begins to collapse
a telescope in which the main light gathering element is a mirror
a telescope in which the main light gathering element is a lens, known as the objective, or object lens
remote sensing
the process of collecting information with instruments that record various forms of energy
the orbital motion of one object around another. The Earth revolves around the Sun in one year. The moon revolves around the Earth in approximately 28 days
to turn around a center point, or axis, like a wheel turns on a bicycle


a small object revolving around a larger object. Satellites can be natural, such as moons, or they can be artificial objects sent into orbit around the earth, such as communication, weather and navigation satellites
shooting star
another name for a meteor
something having to do with the sun
solar flare
a storm or eruption of hot gases on the sun
solar system
the sun, and all the planets and other objects that orbit around it
solar wind
streams of gas particles flowing out from the sun
space probe
an unmanned research spacecraft sent into space
an instrument that breaks up white light from a star into its different colors. This information is used to determine the surface temperature of the star which helps to determine its age
the colors you see when white light is split apart. The order of the colors is: violet, blue, green, yellow, orange, and red. A rainbow is a natural spectrum
speed of light
light travels at 186,000 miles per second, or 299,792,458 meters per second. Albert Einstein predicted that nothing can go faster than the speed of light
a dark area on the sun's surface that is cooler than the area around it
a great explosion that gives off tremendous amounts of light at the end of a star's life cycle. A supernova can become a neutron star or a black hole


an instrument that can make faraway things appear closer. There are optical, reflecting, refracting, radio, and telescopes in space


the space that contains all of the matter and energy in existence


white dwarf
the remains of an old star after it uses its energy. It is a small, faint, whitish star that is very dense
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