On Tue, 04 Dec 2018 13:03:36 -0500, Davoud wrote:
I must confess that I have never heard of a "sidereal hour;"

Then you haven't computed the local altitude or azimuth for a
celestial object either, or it's rise and set time. When doing so,
sidereal time is useful. When doing so for the Sun, you can avoid
sidereal time by using the Equation of Time instead.

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

Nowadays planetarium software takes care of these details for most
stargazers, who are happily unaware of the software's use of sidereal
time.


no such
interval exists in the Système international. An hour is an hour is
an
hour, 3600 seconds. It is the second that is the base unit of time
in
SI units, not the hour, which is too broad a brush.

True. Solar time does not exist in SI either. Only atomic time is
defined in the SI system of units.

And if you want to strictly follow SI, you should avoid using
minutes, hours, days, months, years and instead use KS, Ms, Gs, Ts,
etc etc.

One day = 86.4 ks
One year = ca 31.56 Ms
One human lifetime = ca 2.6 Gs
The age of the universe = ca 0.43 Ps

Sidereal and solar hours aren't the only non-SI units used by
astronomers. We also have the stellar magnitude (apparent, absolute
and bolometric) , the light year and the parsec, solar masses, Earth
masses and the Astronomical Unit. There are probably more non-SI
units used by astronomers.

What about giving a stars apparent brightness in nanolux instead of
its visual magnitude? Or it's absolute brightness in Petalumens? Or
it's bolometric brightness in PW? That's whar we would have to do if
we were to strictly use only SI units.