Lat/Long and timekeeping system for Mars

On Thu, 06 Dec 2018 08:19:22 +0100, Paul Schlyter
wrote:

The Hour Angle of a celestial object, which is needed to compute its
local altitude and azimuth, is most easily computed by subtracting
the object's RA from your local sidereal time. Of course you can
compute your local sidereal time without labeling it as such or even
without even being aware of what it is, but I don't see any
convenient way around computing it if you compute the local altitude
and azimuth for some celestial object.

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.

On Wed, 05 Dec 2018 13:00:32 -0500, Davoud wrote:

*Figuratively speaking. Due to macular degeneration I do not look
through telescopes any more. I can still focus on a laptop display,
however https://www.flickr.com/photos/primeval/30364292358,
https://www.flickr.com/photos/primeval/29296501697.

Very sorry to hear that.
--
Email address is a Spam trap.

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

On Tuesday, December 4, 2018 at 10:28:54 PM UTC-7, Quadibloc wrote:
On Tuesday, December 4, 2018 at 11:39:31 AM UTC-7, Gerald Kelleher wrote:
I am sure the ISIS branch of astronomy would find 'sidereal vs solar'
convictions acceptable

We have not come to destroy, but to fulfill.

And, at least if you go by the Julian calendar, fittingly enough, Sir Isaac Newton
was born on Christmas Day.

John Savard

In a way I didn't notice the role of the International dateline in terms of timekeeping as one day elapses into the next or one rotation follows the last one.

This is the link to the calendar cycle as the continuous flow of days and rotations are sown up within the 1461/4 structure representing a close approximation to 365 1/4 rotations per orbital circuit.

Something else to admire in how two different masterpieces fit together.

Mike Collins wrote:
Quadibloc wrote:
On Wednesday, December 5, 2018 at 10:03:26 PM UTC-7, palsing wrote:

Gerald, are seriously suggesting that, for Mars, the hour, minute and second
will be 'redefined' so that Mars will have a 24 hour rotation period?

You are even more delusional than I thought! Why would this possible be an
advantage in any way?

In fact, *Robert Zubrin* suggested exactly the same thing.

While the SI second will obviously be useful on Mars as everywhere else for
defining the frequencies of radio waves, and so on and so forth, people living
on Mars would want to have a way to refer to *the time of day*, and cutting the
day, nearly as long as the day on Earth, into pieces following the same,
familiar plan used on Earth is the simplest thing to do.

John Savard


Mars wris****ches have existed for years. They are used by the operators of
Mars landers who need to start their shift times earlier every day. Since
the first of these were slowed down Earth time watches they implicitly use
Martian seconds.

https://hackaday.com/2012/09/09/buil...sitys-drivers/

For human settlers on Mars I like the “witching hour� method of Vernor
Vinge from Across Realtime where the standard Earth time is used with an
extra period tagged onto the end of the day. But this would have problems
with geographically (areographically) separated settlements.




The simplest concepts are the easiest to get wrong. Later not earlier.

On Thursday, December 6, 2018 at 11:40:50 AM UTC-7, Mike Collins wrote:

The simplest concepts are the easiest to get wrong. Later not earlier.

Maybe you were thinking of the shorter sidereal day instead of the longer Martian
day.

John Savard

On Thu, 06 Dec 2018 08:21:15 -0700, Chris L Peterson
wrote:
On Thu, 06 Dec 2018 08:19:22 +0100, Paul Schlyter
wrote:

The Hour Angle of a celestial object, which is needed to compute
its
local altitude and azimuth, is most easily computed by subtracting
the object's RA from your local sidereal time. Of course you can
compute your local sidereal time without labeling it as such or
even
without even being aware of what it is, but I don't see any
convenient way around computing it if you compute the local
altitude
and azimuth for some celestial object.

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.

There is always something new to learn..

On Thursday, December 6, 2018 at 2:09:42 PM UTC-8, Paul Schlyter wrote:

There is always something new to learn...

Boy howdy, isn't that the truth...

The system where the average 24 hour day anchored to the sunrise/noon/sunset cycle is converted into constant rotation at a rate of 15 degrees per hour has not been explained before nor has the system where the rotations are used seamless to create the calendar format of 365/366 days. They both come together as the masterpiece that is human timekeeping for those who can follow the close proximity between the planetary cycles and years, 24 days, equable hours, minutes and seconds.

https://www.youtube.com/watch?v=T-g27KS0yiY

It may never happen that the same longitude system nor calendar framework is applied to Mars with its own unique timekeeping divisions on one side and the calendar format on the other but this will not be because the principles aren't there but rather the people who can accept them for Earth.

What a lovely thing to do for people who can do it.