What is the observable Universe?

The observable universe is a term that astronomers use to describe the portion of the entire universe that we can potentially observe. Here are the steps to understand it:

1. The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy.

2. Light travels at a finite speed (approximately 299,792 kilometers per second). This means that when we look at distant objects in the universe, we're actually seeing them as they were in the past. The further away an object is, the further back in time we're seeing it.

3. The observable universe is the part of the universe that we can currently see, because light from those parts has had time to reach us. It's centered on the observer and it's a spherical region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because electromagnetic radiation from these objects has had time to reach the Earth since the beginning of the cosmological expansion.

4. The size of the observable universe is determined by the age of the universe and the speed of light. If the universe is approximately 13.8 billion years old, then light has had 13.8 billion years to travel. This gives us a radius for the observable universe of about 46 billion light years.

5. It's important to note that the observable universe is likely only a small fraction of the entire universe. There may be parts of the universe that are simply too far away for their light to have reached us yet. These regions would be outside our observable universe.