The observable universe contains as many as 100 billion galaxies and extends a billion light-years in every direction.
Keywords: Universe, Light--Speed, Galaxies
Our Milky Way Galaxy was once thought to comprise the entire known universe. Today our universe encompasses many billions of galaxies, and its history can be recounted back to its earliest moments.
Telescopes can easily zoom in on a star. But to see a dim object next to a star, such as a planet, astronomers need to block out the star’s light.
The universe is all the matter, energy, and space that exist. We can observe only a part of it - the observable universe.
All parts of the universe are subject to the same simple laws of nature that we find here on Earth.
The Big Bang is the scientific description of the origin of the cosmos.
Galaxies form and evolve within an expanding and cooling universe. Because light takes billions of years to cross the cosmos, we see distant galaxies as they were at earlier times.
When we look out into space, we also look back into time.
An active galaxy emits up to thousands of times more energy than a normal galaxy.