Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Johann Mahne on 09/08/2011 16:06:12

Title: Do astronomers often use the CGS system?
Post by: Johann Mahne on 09/08/2011 16:06:12: I was glancing through an astromy book by Prof Shu on Amazon,and saw that he was using gram centimeters seconds(CGS).
Seemed strange to me.Do astronomers often use this system?
Title: Do astronomers often use the CGS system?
Post by: graham.d on 09/08/2011 16:31:12: I've never seen that unless it was a joke.

I like to use the PTF system in the microchip industry (PTF is the Pole-Ton-Fortnight system). It turns out that pico-acres is quite a usable unit for measuring chips [;D]
Title: Do astronomers often use the CGS system?
Post by: syhprum on 09/08/2011 21:26:06: Astronomers do in fact use strange olde worlde units, they talk about the energy of colliding galaxies in ergs and wavelengths in angstroms.
you have to be patient and bear with them.
Title: Do astronomers often use the CGS system?
Post by: Geezer on 09/08/2011 23:58:39: Quote from: syhprum on 09/08/2011 21:26:06
Astronomers do in fact use strange olde worlde units, they talk about the energy of colliding galaxies in ergs and wavelengths in angstroms.
you have to be patient and bear with them.

It's not fair! As soon as I had memorized "Go to work on an erg", the bastards changed the rules, and made me switch to joules.

So why don't they call it jouleonomics?
Title: Do astronomers often use the CGS system?
Post by: graham.d on 10/08/2011 12:04:57: Strangely, the semiconductor industry often uses Angstroms for vertical dimensions, nanometers or micrometers for horizontal dimensions, unless at the level where the wafers go for sawing (into chips) then the horizontal dimensions are in Mils (milli-inches). The reasons are historic and geographic.
Title: Do astronomers often use the CGS system?
Post by: yor_on on 12/08/2011 21:26:47: Would that be 'micro geographic's'?
Title: Do astronomers often use the CGS system?
Post by: graham.d on 13/08/2011 07:37:01: Ha ha, no. The geographic relationship is because most people involved in Physics (worldwide) use the metric system, so vertical etched dimensions and optics was always in metric. However, large mechanical devices such as wafer steppers, bonding machines, probers etc., which were initially designed in the USA, were all in Imperial. Early chip horizontal dimensions were also in Imperial (Mils = 10^-3 inches) because this was also commonplace in the USA though this changed, even in the US, around the mid 70's. Now most of the world is metric though there are still some steppers and wafer handling equipment using Mils - actually I don't know many new ones that do that now though some have that as an option. Some device package dimensions are specified in Mils and mm to satisfy the US market and there can still be some restrictions to die sizes to be multiples of 10^-4 inches so that older equipment can be used in assembly.
Title: Do astronomers often use the CGS system?
Post by: Geezer on 13/08/2011 17:37:54: Personally, I prefer to measure everything in mfinches. The mfinch is a fraction of an inch - 1/51 to be precise.

2 mfinches is 1 mm (close enough for government work anyway) so you can get from mfinches to millimeters simply by dividing by two. I'm quite surprised more people don't use this system.
Title: Do astronomers often use the CGS system?
Post by: peppercorn on 13/08/2011 19:38:25: Quote from: Geezer on 13/08/2011 17:37:54
Personally, I prefer to measure everything in mfinches. The mfinch is a fraction of an inch - 1/51 to be precise.

Ho ho! You might as well call them swearword-inches!
[Note-to-self: Avoid starting a 'discussion' on encouraging Americans to use the metric system]
Title: Do astronomers often use the CGS system?
Post by: syhprum on 13/08/2011 19:55:39: I am reminded of the original Harry Potter story where harry visits his bank and find the sub units of his assets are in factors of seventeen and thirteen.
Rather like the olde worlde English system only even worse.
Title: Do astronomers often use the CGS system?
Post by: Geezer on 13/08/2011 20:37:11: Quote from: syhprum on 13/08/2011 19:55:39
I am reminded of the original Harry Potter story where harry visits his bank and find the sub units of his assets are in factors of seventeen and thirteen.
Rather like the olde worlde English system only even worse.

Very astute of you to point that out Syhprum. I'm sure you noted that 51 has the convenient factors of 17 and 3. This allows us to quickly convert 0.3333 inches to 8.5mm without a calculator.
Title: Do astronomers often use the CGS system?
Post by: Geezer on 13/08/2011 21:44:32: BTW, I still have some mfinch rulers in stock at very reasonable prices.

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Title: Do astronomers often use the CGS system?
Post by: Geezer on 15/08/2011 07:12:50: Okdoky!

Well, as I seem to have totally derailed this thread, I might as well continue. (Did anyone count off the divisions to see if there really are 17?)

1/17th of an inch is interesting. It's extremely close to 1.5 mm - 1.4941 mm to be a bit more precise. This means that if you cut a screw thread at 17 threads per inch it will be compatible with a metric thread with a pitch of 1.5 mm.

It's fairly obvious that this was taken into account when SI was established, so I have to conclude that there must have been some underhanded conspiracy to preserve "imperial" measurements, despite a veneer of pretence to the contrary.
Title: Do astronomers often use the CGS system?
Post by: Bored chemist on 15/08/2011 18:53:00: Quote from: syhprum on 13/08/2011 19:55:39
I am reminded of the original Harry Potter story where harry visits his bank and find the sub units of his assets are in factors of seventeen and thirteen.
Rather like the olde worlde English system only even worse.
Do you mean the one we pinched from the French?
http://en.wikipedia.org/wiki/Livre_tournois
(though , to be fair we might have taken it from the Romans and messed with it, just like the French did.)
http://en.wikipedia.org/wiki/Roman_currency
Title: Do astronomers often use the CGS system?
Post by: grizelda on 15/08/2011 22:50:53: All anachronisms now, sadly. The new world is measured in apps. You can hold an iPad over your head at night and see the sky behind it on your screen, with convenient labels.