Newton pointed out that you can calculate the force of gravity between two objects if you know their mass and their distance apart.
Ancient people used the sky as a calendar and a timekeeper.
Dark energy acts opposite gravity and continues to speed up universal expansion today.
The nearest stars are about 4.2 light-years from the Sun.
The Milky Way is moving through space at an estimated velocity of 630 kilometers per second.
Black holes are massive, dense objects with gravity so strong that nothing—not even light—can get out.
Astronomers classify stars by their color, which reveals the temperature at the star’s photosphere (the visible “surface”).
When a star dies, the material it created is distributed into space and recycled into new generations of stars, planets, and life.
The most energetic objects, events, and processes in the universe give off x-rays and gamma rays.
Light can act as a particle, called a photon, or it can travel through space as a wave.
Hubble proved that some distant clouds of light in the sky are actually distant galaxies that lie well beyond the boundaries of our own home galaxy, the Milky Way.