Page 1 of 2 12 LastLast
Results 1 to 15 of 16
Like Tree11Thanks

Thread: Astronomy

  1. #1
    Super Member harpazo's Avatar
    Joined
    Sep 2014
    From
    NYC
    Posts
    995
    Thanks
    42

    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.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Apr 2005
    Posts
    20,249
    Thanks
    3366

    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.
    Thanks from topsquark and harpazo
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    Joined
    Feb 2015
    From
    Ottawa Ontario
    Posts
    2,254
    Thanks
    499

    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!!
    Last edited by DenisB; Jan 9th 2019 at 06:26 AM.
    Thanks from harpazo
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member harpazo's Avatar
    Joined
    Sep 2014
    From
    NYC
    Posts
    995
    Thanks
    42

    Re: Astronomy

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

    3.1536 x 10^(-7)

    Yes?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor
    Joined
    Feb 2015
    From
    Ottawa Ontario
    Posts
    2,254
    Thanks
    499

    Re: Astronomy

    Quote Originally Posted by harpazo View Post
    Ok.
    Then 31,536,000 in scientific notation we write
    3.1536 x 10^(-7)
    3.1536 * 10^7
    Thanks from harpazo
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Senior Member
    Joined
    Jun 2014
    From
    NJ
    Posts
    301
    Thanks
    115

    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} $
    Thanks from harpazo
    Follow Math Help Forum on Facebook and Google+

  7. #7
    MHF Contributor
    Joined
    Oct 2009
    From
    Brisbane
    Posts
    1,231
    Thanks
    454

    Re: Astronomy

    Quote Originally Posted by harpazo View Post
    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
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Super Member harpazo's Avatar
    Joined
    Sep 2014
    From
    NYC
    Posts
    995
    Thanks
    42

    Re: Astronomy

    Quote Originally Posted by Debsta View Post
    see red
    Yes, in one day. Typo at my end.
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Super Member harpazo's Avatar
    Joined
    Sep 2014
    From
    NYC
    Posts
    995
    Thanks
    42

    Re: Astronomy

    Quote Originally Posted by ChipB View Post
    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)?
    Follow Math Help Forum on Facebook and Google+

  10. #10
    MHF Contributor
    Joined
    Feb 2015
    From
    Ottawa Ontario
    Posts
    2,254
    Thanks
    499

    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...
    Follow Math Help Forum on Facebook and Google+

  11. #11
    Super Member harpazo's Avatar
    Joined
    Sep 2014
    From
    NYC
    Posts
    995
    Thanks
    42

    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?
    Follow Math Help Forum on Facebook and Google+

  12. #12
    MHF Contributor
    Joined
    Feb 2015
    From
    Ottawa Ontario
    Posts
    2,254
    Thanks
    499

    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
    Thanks from harpazo
    Follow Math Help Forum on Facebook and Google+

  13. #13
    Senior Member
    Joined
    Jun 2014
    From
    NJ
    Posts
    301
    Thanks
    115

    Re: Astronomy

    Quote Originally Posted by DenisB View Post
    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.
    Thanks from harpazo, topsquark and DenisB
    Follow Math Help Forum on Facebook and Google+

  14. #14
    MHF Contributor
    Joined
    Feb 2015
    From
    Ottawa Ontario
    Posts
    2,254
    Thanks
    499

    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
    Last edited by DenisB; Jan 17th 2019 at 04:09 PM.
    Thanks from harpazo
    Follow Math Help Forum on Facebook and Google+

  15. #15
    MHF Contributor

    Joined
    Apr 2005
    Posts
    20,249
    Thanks
    3366

    Re: Astronomy

    But you don't want to annoy the photon people!
    Thanks from DenisB
    Follow Math Help Forum on Facebook and Google+

Page 1 of 2 12 LastLast

Similar Math Help Forum Discussions

  1. physics/astronomy
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: Nov 19th 2010, 06:26 PM
  2. Maths/astronomy help!
    Posted in the Math Topics Forum
    Replies: 6
    Last Post: Apr 30th 2009, 02:01 AM
  3. Astronomy...Earth
    Posted in the Pre-Calculus Forum
    Replies: 4
    Last Post: Oct 18th 2008, 04:20 AM
  4. Astronomy...Mars
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: Oct 18th 2008, 04:18 AM
  5. Getting confused with astronomy trig
    Posted in the Advanced Algebra Forum
    Replies: 3
    Last Post: Aug 8th 2008, 03:18 AM

/mathhelpforum @mathhelpforum