A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.The word galaxy is derived from the Greek galaxias literally “milky”, a reference to the Milky Way.

Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe.

The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly of the objects that orbit the Sun.

Spaceflight is ballistic flight into or through outer space. Spaceflight can occur with spacecraft with or without humans on board. Yuri Gagarin of the Soviet Union was the first human to conduct a spaceflight

The Universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy.