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

13. ## Re: Astronomy

Originally Posted by DenisB
Yes, but rounded up:

5.866 * 10^12 = 5,866,000,000,000
should be:
5.865696 * 10^12 = 5,865,696,000,000
Be careful not to claim such a high level of precision when the data the calculation is based on is not so exact. We are told the speed of light is 186,000 miles/second, but that's accurate to only 3 decimal places, which means the proper answer to the question can be accurate to only three decimal places as well. Hence 5.87 x 10^12 miles/LY is a better answer than 5.865696 x 10^12 miles/LY given the data provided. If you want an answer with more digits of accuracy you must use a more accurate number for the speed of light. Thus if you use c=186,282 miles/second then you can calculate the length of a light year to 6 decimal places, getting 5.87459 x 10^12 miles.

14. ## Re: Astronomy

Well reeely...anybody travelling at that speed wouldn't give a hoot anyhooo

http://math.ucr.edu/home/baez/physic...measure_c.html

15. ## Re: Astronomy

But you don't want to annoy the photon people!

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