View Single Post
  #53  
Old December 6th 18, 06:23 PM posted to sci.astro.amateur
Quadibloc
external usenet poster
 
Posts: 7,018
Default Lat/Long and timekeeping system for Mars

On Thursday, December 6, 2018 at 8:21:17 AM UTC-7, Chris L Peterson wrote:

Sure, but that's exactly my point. We can understand the concept, but
are still going to have a "huh?" moment if somebody talks about a
"sidereal hour", simply because that's not a conventional term that
anybody really uses.


To me, I'd think that's a rather small "huh?" moment. If the sidereal time can
be 16h 37m, then obviously when the sidereal time is 17h 37m, it must be one
sidereal hour later - so the unit implicitly exists, even if it isn't normally
explicitly mentioned.

One thing that might appear paradoxical at first is this:

Time zones on the Earth, ideally and abstractly, occupy 15 degrees of longitude.

An hour of right ascension on the celestial sphere is also 15 degrees wide.

So if you have two locations on the Earth, separated by 15 degrees of longitude,
their solar time will differ by one hour; *and* their sidereal time will differ
by one sidereal hour, which is shorter.

Of course, there is no contradiction, because even in just one hour, the Earth
will have moved in its orbit around the Sun. So an hour later, both locations
will have advanced by 15 degrees in relation to the mean Sun, and both locations
will have advanced by slightly more than 15 degrees in relation to the celestial
sphere.

John Savard