A light-year is the distance that light travels in one Julian year, which is 365.25 days, as defined by the International Astronomical Union (IAU). Light travels through interstellar space at 186,000 miles per second, which is 5.88 trillion miles per year. If you could travel that fast, you could circle the equator 7.5 times in one second.
It takes 43.2 minutes for sunlight to reach Jupiter, which is around 484 million miles away, whereas it takes about 1.87 years to get to the edge of our Solar System at the furthest edge of the Oort Cloud. To walk a distance of one light-year, at a constant speed of 1.42 metres per second (which is 3.2 mph), would take around 225 million years (11.3 billion days). This is longer than humans have even been around.
The light from the Sun takes 8 minutes to travel the 93 million miles to the Earth, which we call one Astronomical Unit (AU). As objects in our universe are so far away, we use light-years to describe distance for some, however many deep space objects are so far away that we soon end up with impossibly high numbers, even in light-years. Robert Burnham Jr, who was a 20th century astronomer, devised a way to portray these distances, when he observed that the number of AUs in one light-year and the number of inches in one mile are virtually the same ( 63000 and 63360). So, if we scale one AU to one inch then one light-year is equal to one mile.
Alpha Centauri, which is the closest star to Earth, at 4.4 light-years away (after the sun). Using Robert Turnham Jr's scale, it is 4.4 miles away. Sirius would be 8.6 miles away, Vega would 25 miles away and the Pleiades would be 444 miles away. The centre of our galaxy, the Milky Way, would be 26,100 miles away & our closest galaxy (Andromeda galaxy - M31) would be 2,540,000 miles away.
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