How long is a light year?
Ok, let’s work this out properly. A light year is defined as the distance the speed of light in a vacuum can travel in one year as defined by the Julian calendar, that is to say 365.25 days. Now the speed of light in a vacuum is 299,792,458 m/s. Since this is a figure arrived at by definition we know it is precisely accurate. How do we know? Well it is because a metre is defined as the distance the speed of light can travel in 1/299,792,458th of a second, although that was not always the definition of a metre but it is now. There are 100 cm in a metre so the speed of light in a vacuum is exactly 29,979,245,800 cm/s There are 60 seconds in a minute and 60 minutes in an hour that’s 3600 seconds in an hour. Multiply these numbers gives 107,925,284,880,000 cm/h A day is a bit complex, since the earth takes 23hrs 56min 4.091 seconds to rotate about its axis measured using sidereal time, which is further complicated by the fact that the earth wobbles due to precession and nutation and furthe
Why don’t people use COMMON numbers to state one light year. It’s hard enough for beginners to understand without confusing the matter with silly math. One light year is approximately 5,865,696,000,000 trillion miles. At public observing events we just round this up to an easy to remember number: 1 light year is about 6 trillion miles. So the nearest star (system) is about 4 light years away or about 24 trillion miles. http://www.howstuffworks.com/question94.… Look at the good answers above. Do those numbers mean anything to you?
