Observing space allows scientists to peer into the universe’s past. This is possible because light requires time to travel over vast cosmic distances. By capturing light from celestial objects, telescopes act as windows into earlier periods of the universe’s history.
Light travels at approximately 186,000 miles (300,000 kilometres) per second. Despite this incredible speed, the immense distances in space mean that light takes noticeable amounts of time to reach Earth. For instance, the Moon is about 239,000 miles away from Earth, and its light takes 1.3 seconds to arrive. Similarly, light from Neptune, the farthest planet in our solar system, takes approximately four hours to reach us.
Measuring Galactic Distances Through Light
Within the Milky Way galaxy, distances are expressed in light-years, referring to the distance light travels in one year. Proxima Centauri, the closest star to our solar system, is over four light-years away. Observing it reveals how it appeared over four years ago, as the light seen today began its journey then.
Galaxies outside the Milky Way lie even farther away. The Andromeda galaxy, the Milky Way’s nearest large neighbour, is located about 2.5 million light-years away. When scientists study Andromeda, they observe light that began its journey before early humans roamed the Earth.
The Universe’s Oldest Light
The James Webb Space Telescope has the capability to detect light from galaxies billions of light-years away. This light originated when the universe was in its infancy, allowing astronomers to study its early stages. Observations of such distant galaxies provide valuable insights into the universe’s evolution over its 13.8-billion-year history.
Astronomical research using telescopes like Webb has transformed our understanding of time and space, enabling a deeper exploration of the universe’s origins and its continual transformation.