What is the Observable Universe?
The observable universe is the part of the entire universe that we can see and measure from Earth. It includes all the galaxies, stars, and other objects whose light has had time to reach us since the universe began. The edge of the observable universe is not a physical boundary but rather the farthest distance light could have traveled in the 13.8 billion years since the Big Bang.
Size Measurements
Astronomers measure the observable universe as having a diameter of approximately 93 billion light-years. This means if you traveled at the speed of light in one direction from Earth, it would take 46.5 billion years to reach the edge. The universe is larger than you might expect based on its age because space itself has been expanding rapidly since the Big Bang, stretching distances between objects.
Why We Call It Observable
We use the word observable because the entire universe is likely much larger than what we can see. There may be galaxies and objects beyond the 93-billion-light-year boundary whose light has not yet reached Earth. We cannot measure or study these distant regions, so scientists focus on the observable universe that we can actually detect with telescopes and other instruments.
How Scientists Measure It
Scientists determine the size of the observable universe using data from telescopes, measurements of the cosmic microwave background radiation, and observations of distant galaxies. They calculate how fast the universe is expanding and work backward to determine its size at different points in time. These measurements are updated as technology improves and we gather more data. 
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