×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

why 360 degrees?
2

why 360 degrees?

why 360 degrees?

(OP)
Considering radians vs degrees, we engineers know the many advantages of radians.  Degrees has the advantage of representing many common angles as round numbers.  But how did they come up with 360 degrees in a circle?

There are some eerie overlaps with time. The number 60 playing a role. 60 seconds in a minute and 60 minutes in an hour.   6 * 60 degrees in a circle.  Minutes and hours show up as subdivisions of degree.  I can't quite make the connection between time and degrees. Rotation of the earth would seem the logical tie, but doesn't seem to work.  In one hour we should rotate 360 degrees/24 = 15 degrees.  In on minute earth would rotate 15/60 = 1/4 degrees... not the same as one minute angle measure which is 1/60 degree.

So, who came up with 360 degrees in a circle and why?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: why 360 degrees?

Why not?

360 can be handily divided by 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24, 30, 36, 40, 45, 60, 90, 120, 180.  Pretty useful mathematical properties.

RE: why 360 degrees?

Man, for mathematicians they make pretty unconvincing historians!

Supposing there was an ancient astronomer, with a slight fixation on the number 60.

If he was to look up overhead half way between sunset and sunrise every day, after 360 days (roughly) he'd see the same star field, in the same place relative to his surroundings. Every night the star field would rotate by approximately 1/360 of a circle.

Only problem with that is that obviously 360 <> 366.25 (or is it 364.25?), so our observant astronomer is going to see a quite noticeable error in his lifetime, or even 5 years.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: why 360 degrees?

365.25 days/year -> that's why we add one day every 4 years ;) (4*.25)

Maybe the guy thought it was easier to round the number to 360 rather than 365 to make his calculations...

Cyril Guichard
Mechanical Engineer Consultant
France

RE: why 360 degrees?

2
The ancient astronomer was in fact an engineer by training and used a safety factor to arrive at an answer of 360.

corus

RE: why 360 degrees?

so, why couldn't I be sure it was 365.25?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: why 360 degrees?

Babylonians used a base 60 counting system and it all trickled down from there.  How they decided on that, I don't remember, but I'll check.

Took a history of math course as an undergrad.  It was aimed at teachers but since it was a 300 level math class, it counted as a technical elective.  It was that or advanced thermo.  

RE: why 360 degrees?

Wouldn't the signs of the zodiak appear to move through the sky at different rates during different times of the year, depending where on its (elliptical) orbit the earth was?

RE: why 360 degrees?

We're talking SEXAGESIMAL arithmetic with all the 60's in the system.  People raise their eybrows when you say sexigesimal!

The teachers of the ancient Babylonians were aliens with six fingers on each hand, that's where the 60's came from.....

Larry

RE: why 360 degrees?

As I recall some cultures had a 360 day year with a 5 day holiday to take up the slack.  I think the French tried that during the French Revolution when everything was going metric.  Ten months (the metric part) of 36 days each, with a 5 day holiday.  They also tried 10 hour days, with 100 minutes per hour, and 100 rather short seconds per minute.  Never caught on.

Leap years are every year that is divisible by 4, except years that are divisible by 100 are NOT leap years (1900 was not a leap year), except years that are divisible by 400 ARE leap years (2000 was a leap year).

Recently the world has gone off the astronomical clock so time is now determined only by physics via atomic clocks.  Good bye leap-seconds, which were used to reconcile astronomically determined time with time determined by the vibrations of cesium atoms.

RE: why 360 degrees?

jimkirk, now that you speak about that, I remember I learnt something like this in my young age smile Stupid revolutionnary calendar, I never understood it blllttt

Cyril Guichard
Mechanical Engineer Consultant
France

RE: why 360 degrees?

Thanks for the info, Hg.  I'd read that they were already gone.  Looks like the debate continues.  Personally, I like 'em.

Another interesting (at least to me) tidbit, is why there are 180 Fahrenheit degrees between 0 and 100 Celsius degrees.  (180 being 360/2, so this is at most half off topic).  According to Wikipedia, there are several different stories.  

The one I originally heard was that Fahrenheit's original scale was zero for the freezing point of a saturated salt water solution, and 100 degrees for normal human body temperature.  These were fairly constant and readily available reference points.  Another interesting point being that it was based on a nice metric-like difference of 100 degrees.

The Celsius scale originally had zero represent the boiling point of water, and 100 as the freezing point, but Carl Linnaeus suggested reversing it, which was much more popular.  The Farhrenheit scale was later adjusted to even up with the Celsius scale at the 180 to 100 degree ratio, necessitating the change of normal body temperature to the familiar (to Americans, anyway) 98.6 degrees.

RE: why 360 degrees?

Many measurement schemes are based around zero being the lowest sensible value and 100 being the highest.  People just like working in that range. (as an aside, it really bugs me when 30 degrees C is refered to at twice as hot as 15 by some weathermen)  

Just imagine Joe Public being told that new cars' speedometers will now record speed in SI units!

RE: why 360 degrees?

Hi SomptingGuy
As in 16.67 meters per second instead of 60 kilometers per hour?
Respectfully

RE: why 360 degrees?

waross:  Exactly.  When's the last time you did "a ton" in m/s?

RE: why 360 degrees?

km, h, m and s are all SI units

RE: why 360 degrees?

epoisses,

   In a very strict technical sense, the SI system is MKS, standing for meters, kilograms and seconds.  Waross is right. :)

                      JHG

RE: why 360 degrees?

To the original post - you might be interested in the link below.  Surveyors (at least Swedish ones) seem to like to use gons (grads) for surveying where there are 400 gons per the circle.  (Actually had this specified in a contract a few years ago in Laos.).

http://www.mhs.ox.ac.uk/sphaera/index.htm?issue10/articl7

RE: why 360 degrees?

Then there's the two flavours of milliradian - the scientific (with 6283ish in a circle), and the military variant (short-changed again, with only 6200).

A.

RE: why 360 degrees?


We needn't worry, in the short span of some 113 million years in the future, considering the slowering of earth rotation, the year length would be just about 360 days.

RE: why 360 degrees?

Isn't the revolution slowing too?

RE: why 360 degrees?

I hope the five days doesn't come out of our vacation time!!

RE: why 360 degrees?

(OP)
I know they have that leap second adjustment thing.  I guess after awhile we will be able to get rid of leap year.

If it takes 113 million years to get rid of 5 days per year, then I guess in 113/5 ~ 23 million years from now we will have one less day per year.  And in 23/4 ~ 6 million year we will have 1/4 less day per year. No more leap year?

Then after that we'll have to start subtracting days. Do we keep taking them out of February (delete Feb 27 next?), or do we try to even out the months by going taking it out of a 31-day month (I never liked January anyway).

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: why 360 degrees?


Yes, but don't forget days will become less but longer with more daylight and starlight for work or leisure.

RE: why 360 degrees?

zeusfaber:

If I recall correctly, 6400 military millirads make a circle (not 6200). The approximation was made to make mental arithmetic easier for calculations of range in the battlefield. Close enough for government work.

RE: why 360 degrees?

Come to think of it, I think you're right.

The nice thing about mils is that if your first salvo falls ten metres left of a target at one km range, you just need to traverse right ten mil to get the next salvo onto the spot just vacated by the target.

Correction (in mils) = Miss Distance across range (in m) divided by range (in km)

A.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources