Estimation quiz!

[J-F Garnier]

(08-01-2020 05:24 PM)ijabbott Wrote:  A useful approximation for electronics: speed of light ≈ 1 foot per nanosecond.

As a continental european EE, my reference is 30cm for 1ns ...

(08-01-2020 08:41 PM)johanw Wrote:  Are all these ancient units still used in papers? I still remember the scolding I got when I entered wavelengths in Ångström (1Å = \(10^{-10}\)m) in my masters thesis. I had to change it to nm before I could get a passsing grade, the faculty had a strict SI-only policy.

Non-SI units are very common in astronomy, think of the old parsec (distance where a length of 1AU is seen under an angle of 1 arc-second , with 1AU being the average Earth-Sun distance :-)
The parsec seems now less used and often replaced by the light-year (1 pc is about 3 ly), but is still used for instance for the Hubble constant (cosmological expansion) Ho ≈ 70 km/s/Mpc.

Also masses of stars are generally expressed not in kg but in solar mass, and so on.

A funny coincidence: there are (about) as many km in one light-year than Ångström in one km.

J-F