Units of angle and measurement *** (troll warning) ****

[SteveBz]

Hi Guys,

It's always dangerous debating culture and custom, so I'm holding my breath as I write.

I preferred using my first pocket calculator in degrees and not radians as my Maths teacher wanted me to do, but really he was right, radians are the correct mathematical unit of degrees.

So my question is why, in both the scientific and amateur communities do we still use units based on degrees and 17th century navigation systems (seconds of arc).

It seems to me that the correct units of angle are Radians and Steradians (the 3D equivalent) and therefore parsecs should not be parsecs and megaparsecs but par-milli-radians or something and mega-par-milli-radians.  Clearly they sound silly, but they would become streamlined with use, maybe we don't need the milli in there, just parrads and megaparrads.

It would make the calculations so much easier without having to divide things by 360*60*60 or whatever.  For the same reason we no longer use the duodecimal system for money, and even 200p is becoming more prevalent than the good old 8 incher. 

Now I'll duck and I'd like to hear your views both for megaparrads (distance) and microsteradians (3d angle of a star). 

(I'm wearing my tin-foil hat under the table).

Regards

Steve.

[Demonperformer]

First thoughts, off the top of my head, are (1) standard star positions are to at least one, usually two and sometimes even three decimal places of an arcsecond which would be (1/57.3*60*60)/(either 10, 100 or 1000) of a radian and that would be an awful lot of decimal places. (2) The system we have is so universally accepted we would never get people to accept a new one. After all, we still (primarily) use hours, tmins & tsecs for RA measurement and, although some databases list RA positions in degrees, that way of doing things has not taken the astronomical world by storm. I guess astronomers can get stuck in their ways as much as anyone else.

I will now go and get my tin hat and join you under the table, if I may.

[cloudsweeper]

Degrees, minutes, and seconds are convenient units of angular measure.  The radian (57.3 degrees) is arguably not as convenient or easy to imagine.   A 5 degree expanse of sky is a familiar amount, whereas the equivalent 87.3 millirads would take some getting used to, and confuse people considerably.

The radian becomes necessary in angular measure in higher maths where trigonometric functions are used.  "Sin x" for example is defined with the "x" being measured in radians.  When you see "sin pi/4",  the part that the sine function is operating on is pi/4 radians.   (45 degrees.)  So unless you're working with higher trig, trig identities, or integration/differentiation of trig functions, there is no real need to use radians.

Doug.

 

[andrew s]

Units of measure are just a convention. There is no right or wrong just more or less convenient. Often units in which c= h(bar) = 1 are used. In spectroscopy we still use the angstrom rather than nano meters

Regards Andrew  

[Stub Mandrel]

Why not use mils (aside from there being several to chose from).

[SteveBz]

So the angle of the sun is just its diameter in any units divided by its distance in any units.  In km it is just 1.39 x 10^6 / 149 x 10^6 or 9.3 millirads. 

In degrees it is arctan(1.39 x 10^6 / 149 x 10^6) or about .5 degrees.  In radians you don't need to do the arctan for small angles.

It's even more accurate for stars and planets.

[saac]

I agree with Andrew, there is no such thing as the correct unit of measurement. Units should be chosen as those most suited to the given situation. Angular measurement in degrees is perfectly adequate in manufacturing, aviation and engineering. Radians may be more appropriate in academic/theoretical work  (2 pi rads  = 360 degrees) where it lends to convenient mathematical representation.

 

Jim

[Pompey Monkey]

1 foot per nanosecond. - The ancient and the modern come together beautifully.

Just sayin'

[SteveBz]

4 minutes ago, Pompey Monkey said:

1 foot per nanosecond. - The ancient and the modern come together beautifully.

Just sayin'

Perfect, so we're all agreed then.

I was thinking 1 furlong-cubit myself.  But I think you have it.

[Pompey Monkey]

3 minutes ago, SteveBz said:

Perfect, so we're all agreed then.

I was thinking 1 furlong-cubit myself.  But I think you have it.

Lols - I had to look that one up!

[Physicist13]

On 8/3/2016 at 18:01, saac said:

I agree with Andrew, there is no such thing as the correct unit of measurement. Units should be chosen as those most suited to the given situation. Angular measurement in degrees is perfectly adequate in manufacturing, aviation and engineering. Radians may be more appropriate in academic/theoretical work  (2 pi rads  = 360 degrees) where it lends to convenient mathematical representation.

 

Jim

sorry strongly disagree!!! This is whole point of the SI system!!! Units of angle is the radian and should be used. The CIMP recognise other units, such as degrees. With globalisation it is increasingly important that all countries use the same units and with national standards that maintain those units and their traceability to the SI system.

P (metrologist!  )

see www.bipm.org and links also ISO site. plus UK national measurement lab.... npl.co.uk

 

[andrew s]

18 minutes ago, Physicist13 said:

sorry strongly disagree!!! This is whole point of the SI system!!! Units of angle is the radian and should be used. The CIMP recognise other units, such as degrees. With globalisation it is increasingly important that all countries use the same units and with national standards that maintain those units and their traceability to the SI system.

P (metrologist!  )

see www.bipm.org and links also ISO site. plus UK national measurement lab.... npl.co.uk

 

What is the point of the SI system other than an agreed convention. Hardly any professional scientists use it.

Regards Andrew

[Stub Mandrel]

The problem is that scientists use units that make their work easily comparable with what has been done in the past, whilst industry prefers units that are consistent across markets.

[cloudsweeper]

Yes - we have light years, electron volts, PSI etc., all in common and scientific usage.

But I still miss the poundal, the erg, the gilbert, and the slug.

Doug.

[George Jones]

Suppose a distance is given by 1 metre multiplied by the cosine of a measured angle. The angle is measured to be 40 degrees plus or minus 3 degrees. How accurately is the distance known?

[andrew s]

8 hours ago, cloudsweeper said:

But I still miss the poundal, the erg, the gilbert, and the slug

Given the low output of many energy saving light bulbs I am all for the candela to make a come back.

Regards Andrew

[cloudsweeper]

George - 

76.6cm +3.3cm/-3.5cm (asymmetric) - to a higher accuracy than that of the angular measurement.  

Doug.

[cloudsweeper]

And don't forget the mile, the acre, deg Fahrenheit, and mmHg - all still in widespread use.

Doug.

[andrew s]

They can, however, cause problems if you don't know what units you are using e.g.  "A disaster investigation board reports that NASA’s Mars Climate Orbiter burned up in the Martian atmosphere because engineers failed to convert units from English to metric. "  as reported here http://www.wired.com/2010/11/1110mars-climate-observer-report/

Regards Andrew

[Alien 13]

37 minutes ago, andrew s said:

Given the low output of many energy saving light bulbs I am all for the candela to make a come back.

Regards Andrew

I never new it went away, I spent a lot of my time measuring light as an engineer for military equipment and the candela was the preferred unit with UK, USA and the Far eastern forces.

Alan 

[andrew s]

20 minutes ago, Alien 13 said:

I never new it went away, I spent a lot of my time measuring light as an engineer for military equipment and the candela was the preferred unit with UK, USA and the Far eastern forces.

Alan 

Watt! are you kidding me.  

Joking aside Alan, I realise many non SI units are still in common use be it custom and practice or for practical reasons. That is is thrust of the comments I have made.

Regards Andrew

[George Jones]

1 hour ago, andrew s said:

They can, however, cause problems if you don't know what units you are using e.g.

also, the Gimli Glider!

http://blogs.wsj.com/speakeasy/2013/07/23/gimli-glider-pilot-recalls-landing-without-engines-30-years-ago/

https://en.wikipedia.org/wiki/Gimli_Glider

[saac]

11 hours ago, Physicist13 said:

sorry strongly disagree!!! This is whole point of the SI system!!! Units of angle is the radian and should be used. The CIMP recognise other units, such as degrees. With globalisation it is increasingly important that all countries use the same units and with national standards that maintain those units and their traceability to the SI system.

P (metrologist!  )

see www.bipm.org and links also ISO site. plus UK national measurement lab.... npl.co.uk

 

Could not disagree more, every aircraft that you have ever flown in had a fuel load calculated in lbs.  The pilot controlled pitch not in radians but in degrees and of course monitored their airspeed in kts and not meters per second. This is not a debate about the merits of the SI system, simply a recognition that units of measurement should be chosen for their suitability to the particular application. As a Physics teacher I recognize the value and appropriateness of the SI system, as an aircraft engineer, I recognize the practicality and versatility of diverse  measurement systems in the real world.

 

Jim