accuracy with planetary pointing


Roland Christen
 

In a message dated 8/16/00 1:05:30 PM Central Daylight Time,
visonneau-vin@infonie.fr writes:

<< have some trouble with my 900Gto when i want to see object of solar
system,the pointing is always out. >>

If you are in France, you should use time zone 0 in your location and turn
the clock back by 1 hour. This will make your solar system objects come in
closer. For some reason, France has chosen to be in time zone 1, but this is
really only accurate for the real time zone 1 which is centered at 22.5
degrees east, near Belgrade. There have been no changes in the calculations
of the planet data since the beginning. Even the latest version that we are
working on is still the same.

Roland Christen


visonneau-vin <visonneau-vin@...>
 

Hi
I have some trouble with my 900Gto when i want to see object of solar
system,the pointing is always out.My ota isn'nt perfectly orthogonal but the
precision when i point deep sky oject is sufficient.The version of my keypad
is 2.4,is there a problem with my keypad,i don't remember exactly but i
thought there is some problem (bad accuracy for system solar oject) with
oldest version.
When will be available the download area?
Bye
Vincnet from france


Roland Christen
 

In a message dated 8/16/00 3:09:07 PM Central Daylight Time,
terry@venus.sunquest.com writes:

<<
But I'm trying to understand the situation here. It sounds like you'd be
jiggering the *civil* time to help with planetary position calculations,
and that makes no sense to me.>>

Yes, of course, but "civil time" is not accurate when it comes to stellar
time. Civil time can be off by as much as 1/2 hour if you are located near
the edges of your time zone. Further more, in the case of Europe, some
countries have chosen to be in the wrong time zone. In their case, at 12 noon
"civil time" the sun is 2 hours off the meridian in the summer, and 1 hour
off in the winter. If you use this civil time, then the calculated zenith
crossing faithfully recreates this 1 hour discrepancy. There is no way
around, except to adjust the time zone and clock time to correspond to what
is actually happening on the sky.

In the case of the US mainland, the most you will be off with the meridian
swap would be about 1/2 hour at the edges of the time zones. This applies
ONLY to the meridian swap, has nothing to do with the pointing accuracy of
the mount. That is fixed by your initial synchronization on a known star. We
always know where any other point in the sky is, because the distances are
known and fixed.

Roland Christen

>>I would have thought you'd just tell the mount its latitude and longitude,
set its clock to Universal Time, align it, >>


Terry R. Friedrichsen <terry@...>
 

If you are in France, you should use time zone 0 in your location and
turn the clock back by 1 hour. This will make your solar system objects
come in closer.
OK, I'm just a lurker here; my 1200GTO isn't due yet for another couple of
months. So if I should just shuddup and wait for the user manual, some-
body *please* tell me so.

But I'm trying to understand the situation here. It sounds like you'd be
jiggering the *civil* time to help with planetary position calculations,
and that makes no sense to me.

I would have thought you'd just tell the mount its latitude and longitude,
set its clock to Universal Time, align it, and be off and running (or may-
be you hafta set the time on the hand controller; I'm not really clear on
what the division of labor is between the two). In any case, I can't under-
stand what your time zone would have to do with astronomical object position
calculation, planetary or otherwise.

Could someone Enlighten me, please?

Thanks!

Terry R. Friedrichsen

terry@venus.sunquest.com


Roland Christen
 

In a message dated 8/17/00 9:19:49 AM Central Daylight Time,
terry@venus.sunquest.com writes:

<<
Problems like this are exactly why I don't understand why the mount uses
civil time at all.
>>

I doesn't use civil time, it uses universal time, but most people don't have
access to this number, so me made it so that they can input their local time,
and calculate the universal time from it. I don't understand the problem? Do
you think this makes the pointing accuracy less? I can assure you that it
does not for the vast majority of users. Even if you told the mount you were
in Australia, you would still find every star and deepsky object in your
eyepiece.

Roland Christen


Terry R. Friedrichsen <terry@...>
 

Yes, of course, but "civil time" is not accurate when it comes to stellar
time. Civil time can be off by as much as 1/2 hour ...
And, as you pointed out, it can get even worse. Thanks to the "first dawn
of Y2K" flap back on January 1, there is an uninhabited island out in the
Pacific that's something like *5 hours* ahead of mean solar time. (So it
is logically west of the International Date Line even though it is physic-
ally way *east* of the International Date Line, which made the sunrise that
should have been the morning of December 31 became the morning of January
1, by fiat.)

Problems like this are exactly why I don't understand why the mount uses
civil time at all.

(There are lots of fun facts about timezones codified in the Unix zoneinfo
files. Have you ever heard of "Pacific Presidential Election Time"? Or
didjuh know that Hawaii observed Daylight Savings Time for *one day* in
1933?)



There is no way
around, except to adjust the time zone and clock time to correspond to
what is actually happening on the sky.
If you're using civil time, yes. I just find it odd that the mount would
have anything to do with civil time at all, when latitude/longitude/GMT
solves all these problems, including meridian swap.



That is fixed by your initial synchronization on a known star.
So if I understand what you're saying here, you tell the mount the civil
time, which it uses to compute when to do the meridian swap. Synchro-
nizing on a known star then tells the mount how it is oriented relative
to the sky, and it goes from there.

This raises LOTS more questions, but I'm gonna wait for my mount to get
here so I can absorb the manual before asking ...

Thanks for the response.

Terry R. Friedrichsen

terry@venus.sunquest.com


Terry R. Friedrichsen <terry@...>
 

it uses universal time, but most people don't have
access to this number, so me made it so that they can input their local
time, and calculate the universal time from it.
Sounds like a good idea to me.



I don't understand the problem? Do
you think this makes the pointing accuracy less? I can assure you that it
does not for the vast majority of users.
I was simply confused because the original question on this thread was about
inaccuracy in locating the planets and the suggested fix was to change the
timezone. I wanted to understand how that would fix the problem.

I still don't understand the bit about "for the vast majority of users", but
I'm willing to wait for my mount and manual ...

Terry R. Friedrichsen

terry@venus.sunquest.com


Roland Christen
 

In a message dated 8/17/00 9:10:32 PM Central Daylight Time,
terry@venus.sunquest.com writes:

<<
I was simply confused because the original question on this thread was about
inaccuracy in locating the planets and the suggested fix was to change the
timezone. >>

Of course, you have to understand that the planets move from hour to hour,
and will be off slightly if the wrong time has been entered. They are also in
slightly different locations with respect to the background stars depending
on time and location on the earth. This is especially so for the Moon. We
have checked and triple checked our planetary positions against other
standards and against The Sky software, and are within 30 to 60 arc seconds
in position.

Roland Christen