astronaut: Someone trained to travel into space for research and exploration.

current: A fluid — such as of water or air — that moves in a recognizable direction. (in electricity) The flow of electricity or the amount of charge moving through some material over a particular period of time.

DNA: (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

football field: The field on which athletes play American football. Owing to its size and familiarity, many people use this field as a measure of how big something is. A regulation field (including its end zones) runs 360 feet (almost 110 meters) long and 160 feet (almost 49 meters) wide.

International Space Station: An artificial satellite that orbits Earth. Run by the United States and Russia, this station provides a research laboratory from which scientists can conduct experiments in biology, physics and astronomy — and make observations of Earth.

microbe: Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

moon: The natural satellite of any planet.

orbit: The curved path of a celestial object or spacecraft around a galaxy, star, planet or moon. One complete circuit around a celestial body.

Pacific: The largest of the world’s five oceans. It separates Asia and Australia to the west from North and South America to the east.

planet: A large celestial object that orbits a star but unlike a star does not generate any visible light.

robot: A machine that can sense its environment, process information and respond with specific actions. Some robots can act without any human input, while others are guided by a human.

solar: Having to do with the sun or the radiation it emits. It comes from sol, Latin for sun.