Scientific Measurements

1. The Observable Universe: A Sphere of Light

• Size: What we can currently see and measure, known as the "observable universe," is estimated to be about 93 billion light-years in diameter.
• What this means: A light-year is the distance light travels in one year (about 9.46 trillion kilometers or 5.88 trillion miles). So, the light from the very edge of the observable universe has taken roughly 13.8 billion years to reach us (the age of the universe). However, due to the expansion of space itself during that time, those distant objects are now much farther away – hence the 93 billion light-year diameter.
• Content: Within this observable sphere, astronomers estimate there are hundreds of billions to possibly two trillion galaxies. Each of these galaxies, like our own Milky Way, can contain hundreds of billions of stars. The number of stars is often estimated to be more than all the grains of sand on all the beaches on Earth.