The big yellow shell depicts a light-year; the smaller yellow shell depicts a light-month. Read an ext about this image at Wikimedia Commons.

You are watching: How many au are in a light year

Objects in our universe are extremely far away. They’re so much away that kilometers or mile aren’t a valuable measure of your distance. So we speak of an are objects in terms of light-years, the distance light travel in a year. Irradiate is the fastest-moving ingredient in our universe. It travel at 186,000 mile per second (300,000 km/sec). And also thus a light-year is 5.88 sunshine miles (9.46 sunshine kilometers).

But stars and nebulae – not to cite distant galaxies – are vastly farther 보다 one light-year away. And, if we try to to express a star’s distance in miles or kilometers, us soon finish up with impossibly vast numbers. However miles and kilometers are what most of us use to understand the distance from one place on earth to another. In the late 20th century astronomer Robert Burnham, Jr. – author of Burnham’s Celestial Handbook – devised one ingenious means to portray the street of light-years in regards to miles and kilometers.

Keep reading, because that a method to understand the vastness that the universe, using devices of street we know and use every day.

Burnham started by relating the light-year come the huge unit – the Earth-sun distance.

One expensive unit, or AU, equals around 93 million miles (150 million km).

Another way of looking in ~ it: the expensive unit is a bit more than 8 light-minutes in distance.

A light beam bring away 8 minutes to travel the 93 million miles (150 million km) from the sunlight to the Earth. Picture via Brews Ohare/ Wikimedia Commons.

A light-year, pictured together a mile

Robert Burnham noticed that, quite by coincidence, the variety of astronomical units in one light-year and the number of inches in one mile room virtually the same.

For general reference, there are 63,000 huge units in one light-year, and 63,360 inches (160,000 cm) in one mile (1.6 km).

This wonderful coincidence enables us to lug the light-year down to Earth. If we scale the astronomical unit – the Earth-sun distance – at one inch, climate the light-year top top this range represents one mile (1.6 km).

The closest star to Earth, various other than the sun, is Alpha Centauri at some 4.4 light-years away. Scaling the Earth-sun distance at one inch places this star in ~ 4.4 mile (7 km) distant.


The red star in the facility of this picture is Proxima Centauri, our sun’s nearest neighbor amongst the stars. A beam of irradiate from this star takes about 4 year to travel to Earth. Picture via Max Planck Institute because that Extraterrestrial Physics.

Familiar space objects, conceptualized

Scaling the huge unit at one customs (2.5 cm), here are ranges to assorted bright stars, star clusters and also galaxies:

Alpha Centauri: 4.4 miles (6.4 km)

Sirius: 8.6 mile (14 km)

Vega: 25 miles (40 km)

Pleiades open up star cluster: 444 mile (715 km)

Antares: 555 mile (893 km)

Hercules globular star swarm (aka M13): 22,200 miles (35,700 km)

Center of our Milky means galaxy: 26,100 miles (42,000 km)

Great Andromeda galaxy (M31): 2,540,000 miles (4,100,000 km)

Sombrero galaxy (M104): 28,000,000 miles (45,000,000 km)

Whirlpool galaxy (M51): 31,000,000 mile (50,000,000 km)

And therefore on, back to roughly 13 billion+ light-years to the farthest galaxies: 13,000,000,000 miles (21,000,000,000 km)

Okay, the numbers space still pretty big! yet hopefully lock can aid you check out that our cosmos is very vast.

There room 33 stars in ~ 12.5 light years of ours sun. Click right into Atlas that the universe to uncover an interactive page that’ll permit you store zooming farther and also farther out. Picture via Atlasoftheuniverse.com.

The fastest-moving ingredient in the universe

As mentioned above, irradiate travels at an tremendous 186,000 mile per 2nd (300,000 km/sec). That’s really fast. If you might travel in ~ the speed of light, friend would have the ability to circle the Earth’s equator around 7.5 time in just one second!

In various other words, a light-second is the street light travel in one second, or 7.5 times the distance roughly Earth’s equator. A light-year is the distance light travels in one year.

How far is that? multiply the variety of seconds in one year by the variety of miles or kilometers the light travel in one second, and there you have it: one light-year. It’s around 5.9 trillion miles (9.5 trillion km).

This range starts close come home yet takes united state all the method out to the Andromeda Galaxy, the most distant object most people can see with the unaided eye. Photo via Bob King/ Skyandtelescope.com.

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Bottom line: Here’s a way to recognize the range of light-years in miles and also kilometers.