Proxima Centauri is 4.2 light years from Earth, a distance that would take about 6,300 years to cover with current technology. Such a journey would take many generations. In fact, most of the humans involved would never see the Earth or its exoplanetary counterpart. One of the most distant exoplanets we know of in the Milky Way is Kepler-443b.
Traveling at the speed of light, it would take 3000 years to get there. Or 28 billion years, going at 60 miles per hour. So it would take 25,000 years to get there if you traveled at the speed of light. Actually, that's the amount of time it would take from the perspective of the outside world.
From the perspective of a traveler moving at the speed of light, it seems that it doesn't take any time. This is due to the relativistic dilation of time, as explained here. Although modern astronomers tend to prefer to use parsec, light-years are also popularly used to measure the stretches of interstellar and intergalactic space. The TRAPPIST-1 system is made up of seven planets, all roughly in the size range of the Earth, that orbit a red dwarf star about 40 light-years away.
The light-year is most commonly used to express distances to stars and other distances on a galactic scale, especially in non-specialized contexts and in popular scientific publications. And it took almost a decade for New Horizons to get from Earth to Pluto, which is just around the corner, 4.6 light-hours away. If you're wondering, there are only about 31,500,000 seconds in a year, and if you multiply that by 186,000 (the distance light travels every second), you get 5.9 trillion miles (9.4 trillion km) of the distance light travels in a year. Before 1984, the tropical year (not the Julian year) and a measured speed of light (not defined) were included in the IAU Astronomical Constant System (196), used between 1968 and 1983.You may have resisted expressing distances in light-years because it would reduce the accuracy of your parallax data when multiplied by the uncertain parameter of the speed of light.
Light crosses interstellar space at 186,000 miles (300,000 kilometers) per second and 5.88 trillion miles (9.46 trillion kilometers) per year. Distances between objects within a star system tend to be small fractions of a light-year and are usually expressed in astronomical units.
