What Is a Light-Year?

[Admin]

A light-year is a measurement of the distance light travels in a single Earth year, which is important for measuring the vast distances of space

What Is a Light-Year? : Read more

 

[Pogo]

It’s a matter of convenience. We like simple numbers. We measure our height in centimeters, inches, feet/inches, driving distances in kilometers, miles. It’s easier to say some light years instead of kazillions of kilometers or miles. Same goes for mass, area, and so forth. Easier to say sun masses, Jupiter masses, Earth masses, etc.

 

[rod]

"One estimate puts the diameter of the known universe at 28 billion light-years in diameter."

My observation. This is based upon BB cosmology and light-time since BB event, 13.8 billion years ago, thus a radius as measured from Earth. Currently the CMBR redshift is considered some 1100 or so. Cosmology calculators show the comoving radial distance from Earth is some 46 billion light years so the diameter today is some 92 or 93 billion light years across. This radius presented shows most of the universe in the BB cosmology, at present is not observable from Earth.

 

[Pogo]

I was in the U.S. Navy in the early 1970s. In nuclear power school, early on in physics class, we learned that we measure the cross sectional area of an atom in barns which is 1x10^24 cm^2, easier to comprehend than a long decimal of cm^2. One homework question was that given a radius of the universe of some number of light years and that one light years was 5.88x10^12 miles. What is the cross sectional area of the universe in barns? A good math exercise and a good exercise in using scientific notation.

 

[Helio]

I was in the U.S. Navy in the early 1970s. In nuclear power school, early on in physics class, we learned that we measure the cross sectional area of an atom in barns which is 1x10^24 cm^2, easier to comprehend than a long decimal of cm^2. One homework question was that given a radius of the universe of some number of light years and that one light years was 5.88x10^12 miles. What is the cross sectional area of the universe in barns? A good math exercise and a good exercise in using scientific notation.

I've wondered when a large exponent causes cognitive loss of the subject. I'm sure it varies with the topic. The no. of sands on all the beaches might be one interesting enough. But more than a few barns will put the average listener "out to pasture", IMO.

In 1970, as I recall, the Navy worked hard to recruit us engineers for nuclear ships. It looked interesting. I enjoyed recently watching the movie on Rickover.

 

[Pogo]

The Navy recruiter actually gave me a test to see if I had the aptitude, and got me interested. This was September of 1968, entered February, 1969, ‘til May, 1975.