astrophysicist: A scientist who works in an area of astronomy that deals with understanding the physical nature of stars and other objects in space.
atom: The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.
Big Bang: The rapid expansion of dense matter and space-time that, according to current theory, marked the origin of the universe. It is supported by astronomers’ current understanding of the composition and structure of the universe.
black hole: A region of space having a gravitational field so intense that no matter or radiation (including light) can escape.
cloud: A plume of molecules or particles, such as water droplets, that move under the action of an outside force, such as wind, radiation or water currents.
computer model: A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.
cosmos: (adj. cosmic) A term that refers to the universe and everything within it. A scientist who studies the origin and development of the cosmos, or universe, is known as a cosmologist.
dark matter: Physical objects or particles that emit no detectable radiation of their own. They are believed to exist because of unexplained gravitational forces that they appear to exert on other, visible astronomical objects.
element: A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.
fusion: (v. to fuse) The merging of two things to form a new combined entity. (in physics) The process of forcing together the nuclei of atoms. This nuclear fusion is the phenomenon that powers the sun and most other stars, producing heat and forging the creation of new, heavier elements.
galaxy: A group of stars — and usually invisible, mysterious dark matter — all held together by gravity. Giant galaxies, such as the Milky Way, often have more than 100 billion stars. The dimmest galaxies may have just a few thousand. Some galaxies also have gas and dust from which they make new stars.
gravity: The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
helium: An inert gas that is the lightest member of the noble gas series. Helium can become a solid at -272 degrees Celsius (-458 degrees Fahrenheit).
hydrogen: The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues. It’s made of a single proton (which serves as its nucleus) orbited by a single electron.
mass: A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.
matter: Something that occupies space and has mass. Anything on Earth with matter will have a property described as “weight.”
meld: A verb meaning to fully blend or merge together (as when two fatty solids are melted and then stirred until fully mixed in a pot).
model: A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.
orbit: The curved path of a celestial object or spacecraft around a galaxy, star, planet or moon. One complete circuit around a celestial body.
particle: A minute amount of something.
physicist: A scientist who studies the nature and properties of matter and energy.
pressure: Force applied uniformly over a surface, measured as force per unit of area.
Proceedings of the National Academy of Sciences: A prestigious journal publishing original scientific research, begun in 1914. The journal’s content spans the biological, physical and social sciences. Each of the more than 3,000 papers it publishes each year, now, are not only peer reviewed but also approved by a member of the U.S. National Academy of Sciences.
star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
sun: The star at the center of Earth’s solar system. It is about 27,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.
telescope: Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.
universe: The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).
wavelength: The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.