Distances to stars stretch our sense of scale so far that traditional units fall short. The nearest star is about 38 trillion kilometres away, a number this huge demands a different measure. And many other stars sit far beyond that distance, billions of times farther still. People don’t like writing or talking about numbers with twenty digits, but space demands a new kind of math.
For cosmic distances scientists use the time light needs to travel. Light moves at about 300,000 kilometres per second, and nothing known travels faster than light, so distance becomes a measure of time.
Even traveling at the speed of light, it would take roughly 160,000 years to reach the object in this photo. The cloud sits in the Large Magellanic Cloud, a nearby satellite galaxy of the Milky Way. In the image, the glowing cloud labeled NGC 2035, is commonly nicknamed the Dragon Head Nebula and is seen on the right.
These clouds of gas and dust glow because they are home to hot newborn stars and to the remnants of stars that exploded in brilliant supernovae. The bright colors come from gas being heated by starlight and by energetic events as stars form and die in dramatic fashion.
To grasp the sheer size, scientists use the light-year, the distance light travels in a year. Each of these clouds spans hundreds of light-years across. The Large Magellanic Cloud itself is enormous, yet when compared with the Milky Way it appears relatively modest, stretching about 14,000 light-years and about one tenth the size of our galaxy.
Cool Fact
If the eye scans the night sky, the most distant object visible without optical aid is the Andromeda Galaxy, more than two and a half million light-years away. Its brightness, despite the vast distance, shows how massive it is and how far our own galaxy sits from it.