Looking at the sky alone, it is not possible to directly comprehend the size of the entire universe. The universe is vast and expansive, containing billions of galaxies, each consisting of billions of stars. The observable universe, which is the portion of the universe we can currently see, is estimated to be about 93 billion light-years in diameter. However, the universe itself may be much larger than what we can observe.
When we gaze at the night sky, we are primarily seeing objects within our own galaxy, the Milky Way, and a few other nearby galaxies. The distances between these objects are still incredibly immense on a human scale, but they represent only a minuscule fraction of the entire universe.
To gain a deeper understanding of the size of the universe, scientists rely on various methods such as measuring the redshift of distant galaxies, studying the cosmic microwave background radiation, and using mathematical models based on our current understanding of the universe's expansion.
Through these methods, scientists have estimated that the universe is extraordinarily vast, spanning an immense volume beyond our comprehension. The true size and nature of the universe continue to be subjects of ongoing research and exploration in the field of cosmology.