What is a light year?

Question

Someone was talking about how big space is. It must be thousands of miles big, it looks so big. But i keep hearing about "light years" and I don't have a clue what it means, is it a measurement? I'm guessing it's a few hundred miles or something.

Answer 1

A few thousand miles?

I remember when I was at your stage learning about Astronomy, I was amazed and so should you be...

Consider Light rays travelling at 186,000 miles in ONE second. Immagine that huge distance, immagine the distance they travel at that speed for a whole year, THAT is a light year. About 30 Trillion Kilometers.

Light years are still quite small units of measurement considering that some of the most distant stars are some 12 Billion Light year away.

Answer 2

A light year is the distance that light travels in one year. The speed of light is 186,287.5 miles per second. You can find out the number of seconds in a year by multiplying the number of seconds in a minute (60) by the number of minutes in an hour (60). Then multiply that by the number of hours in a day (24), and multiply that by the number of days in a year (approximately 365.25).

So we've got 60 x 60 = 3600 seconds in an hour
3600 x 24 = 86400 seconds in a day
86400 x 365.25 = 31,557,600 seconds in a year.

So a light year is about (I've rounded off a bit) 5,878,786,100,000 miles. That's almost 6 trillion miles. The distance from the earth to the Sun is 93 million miles. The distance to the nearest star is 4.3 light years, and the distance to the Andromeda galaxy is 2 million light years.

The universe is a big place !

Answer 3

A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance that light travels in a vacuum in one year. While there is no authoritative decision on which year is used, the International Astronomical Union (IAU) recommends the Julian year. Numerical value
A light-year is equal to:

9,460,730,472,580.8 km (about 9.461 Pm)
5,878,625,373,183.61 statute miles
about 63,240 astronomical units
about 0.3066 parsecs
The exact length of the light-year depends on the length of the reference year used in the calculation, and there is no wide consensus on the reference to be used. The figures above are based on a reference year of exactly 365.25 days (each of exactly 86,400 SI seconds). This is the value recommended by the IAU. However, other reference years are often used (e.g. Yahoo's and Google's calculators use a smaller value than the IAU), thus the light-year is not an appropriate unit to use when extremely high precision is required.

The IAU Style Manual[1] recommends the use of Julian calendar years (not Gregorian) of 365.25 days, or exactly 31,557,600 seconds. This gives the light-year an exact value of 9,460,730,472,580,800 metres.

The light-year is often used to measure distances to stars. In astronomy, the preferred unit of measurement for such distances is the parsec, which is defined as the distance at which an object will generate one arcsecond of parallax when the observing object moved one astronomical unit perpendicular to the line of sight to the observer. This is equal to approximately 3.26 light-years. The parsec is preferred because it can be more easily derived from, and compared with, observational data. However, outside scientific circles, the term light-year is more widely used.

Answer 4

It's the distance it takes light to travel in 1 year

about 9,500,000,000,000 kilometers or 5,878,786,100,000 miles

While this distance may see huge, it is actually small in comparison to the size of the entire universe. Besides the sun, the nearest star is over 4 light years away from Earth.
When looking into the night sky at that star (proxima centauri) you are actually seeing the light it emitted over 4 years ago. If it were to explode today, we would not see it for 4 years.

I hope this helps.

Answer 5

A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance that light travels in a vacuum in one year. While there is no authoritative decision on which year is used, the International Astronomical Union (IAU) recommends the Julian year.
1 light-year = SI units
9.461×1012 km - 9.461×1015 m
Astronomical units
63.24×103 AU 0.3066 pc
US customary / Imperial units
5.879×1012 mi /31.04×1015 ft

Why don't you google it and read the answers there?

Answer 6

A 'light year' is the distance light travels in one year and equals 5.878499814^12 miles. A 'light year' then is a distance measurement.

Answer 7

Light Year is the light that travels a year.1 light yar is equal to 5,833,333,333,333.
If you can travel at the speed of light you can reach the Moon in 1.2 light secons and the Sun in 8 light minutes and the nearest star the Proxima Centauri is 4.2 light years away.

Answer 8

First, it is a measurement of distance not time. It is the distance that a beam of light would travel in on year. Light travels at 186,000 miles per second. There are 31,536,000 seconds in a year. Thus a light year is 5,865,696,000,000 miles. 186,000 miles per second x 31,536,000 seconds per year = 5,865,696,000,000 miles.

Answer 9

A light year is the distance light travels in one year. A light year is 5,880,000,000,000 miles. Check out my source. Hope I helped :)

Answer 10

1 light year = 9.4605284 × 1015 meters is the exact measurement. in a detailed description a light year is the exact distance light will travel in a vacuum in one year