How far is a light year?

With all this talk about light years, it may help to truly know how far a light year really is. A light year is an astronomical measure of distance. As defined by the International Astronomical Union, a light year is the distance that light travels in a complete vaccuum in one Julian year, which is about 5,878,630,000,000 miles. So many miles is really hard to comprehend, so to put this into perspective, it is about 3300 miles across the United States from Maine to California. If you traveled back and forth across the country until you went as far as light would travel in a year, you would have to drive coast to coast 1,781,403,030 times! Thats right, almost 2 billion times. In terms of the entire world, which has a circumference of 24,901.55 miles at the equator, you would need to circle the entire planet nearly 236,074,863 times! Our sun is about 93,000,000 miles away from the Earth. If we traveled to the sun and back 31,606 times, we would have finally traveled as far as light does in one year. Now that you know how far a light year is, you can begin to grasp how large our galaxy and the Universe really are.

Saturn's Night Side

The Cassini Robotic Spacecraft, now orbiting Saturn, took this image as it made its way into Saturn's shadow. Many new discoveries have been made from this picture. The planet's rings are so brightly illuminated that new rings were found. The outermost ring in the picture is Saturn's E ring, created by ice-fountains on its moon Enceladus, seen here in great detail like never before. Also, the night side of Saturn, a side never before seen, is partially brightened by reflecting light off the rings. Finally, about 746 million miles off in the distance, just above the rings on the left, is the faint light of Earth.

The Carina Pillar and Jets (Infared Light)

This image of the Carina Pillar shows its jets in great detail. The two jets shoot out materials from a young, very hot star nearly 3 lightyears across. Also shown are the newly forming stars that are hidden behind the dust and gas in visible light.

The Carina Pillar and Jets

This pillar of dust and gas is found nearly 7,500 lightyears away. Newly formed stars are still appearing inside this massive pillar, which is estimated to be 2 lightyears wide.