1. Astronomy

One light-year is defined by astronomers to be the distance that a beam of light will travel in one year (365 days). If the speed of light is 186,000 miles per second, how many miles are in a light year? Express your answer in scientific notation.

Let's see.

One day = 24 hours

One hour = 3600 seconds

24(3600) = 86,000 seconds in one year

I am stuck here.

2. Re: Astronomy

You are given that the speed of light is 186,000 miles/second- that is, that light travels 186,000 miles every second- so in two seconds will have traveled 2*186,000 miles, in 3 seconds will have traveled 3*186,000 miles, etc. You have calculated that there are 86,000 seconds/year. How far will light have traveled in 86,000 seconds.

You can also observe that $\displaystyle \frac{miles}{second}\times \frac{seconds}{year}= \frac{miles}{year}$ since the "seconds" cancel.

3. Re: Astronomy

distance = speed * time

speed = 186,000
time = 365 * 24 * 60 * 60 = 31,536,000

Hmmm...wonder if that's the speed of "His coming"....
If so, He'll need a good set of brakes!!

4. Re: Astronomy

Ok. Then 31,536,000 in scientific notation we write

3.1536 x 10^(-7)

Yes?

5. Re: Astronomy

Originally Posted by harpazo
Ok.
Then 31,536,000 in scientific notation we write
3.1536 x 10^(-7)
3.1536 * 10^7

6. Re: Astronomy

You have determined that there are 3.15 x 10^7 seconds in a year. Now multiply that by 186,000 miles per second to get the number of miles in a light year:

$186000 \frac {miles}{second} \ \times \ 3.15(10)^7 \frac {seconds}{year} \ = \ ?? \frac {miles}{year}$

7. Re: Astronomy

Originally Posted by harpazo
One light-year is defined by astronomers to be the distance that a beam of light will travel in one year (365 days). If the speed of light is 186,000 miles per second, how many miles are in a light year? Express your answer in scientific notation.

Let's see.

One day = 24 hours

One hour = 3600 seconds

24(3600) = 86,000 seconds in one year day??

I am stuck here.
see red

8. Re: Astronomy

Originally Posted by Debsta
see red
Yes, in one day. Typo at my end.

9. Re: Astronomy

Originally Posted by ChipB
You have determined that there are 3.15 x 10^7 seconds in a year. Now multiply that by 186,000 miles per second to get the number of miles in a light year:

$186000 \frac {miles}{second} \ \times \ 3.15(10)^7 \frac {seconds}{year} \ = \ ?? \frac {miles}{year}$
Are you saying to do this (3.1536 * 10^7)(186,000)?

10. Re: Astronomy

What is the big mystery here?

There are:
365 * 24 * 60 * 60 = 31,536,000 seconds in a year
or (to average out leap years):
365.25 * 24 * 60 * 60 = 31,557,600 seconds in a year

Over and out...

11. Re: Astronomy

Here it is:

(1.86 * 10^5) * (60 * 60) * (24 * 365)
(1.86 * 10^5) * (3.6 * 10^3) * (8.76 * 10^3)
(1.86 * 3.6 * 8.76) * 10^11
58.66 * 10^11
5.866 * 10^12

Yes?

12. Re: Astronomy

Yes, but rounded up:

5.866 * 10^12 = 5,866,000,000,000
should be:
5.865696 * 10^12 = 5,865,696,000,000