Concept
The Celestial Sphere
The sky as a giant rotating dome.
An imaginary sphere surrounding Earth onto which all stars are projected. Astronomers use coordinates (right ascension & declination) to map positions, just like longitude and latitude on Earth.
See also
The Big Bang
How everything began, 13.8 billion years ago.
Black Holes
Regions where gravity stops light itself.
Dark Matter
The invisible mass holding galaxies together.
Dark Energy
The mysterious force accelerating the universe.
Light-Year & Astronomical Distances
Measuring the unimaginable.
Gravity
The force that shapes the universe.