Lunar Tracking question please

[Doink]

Greetings

To date, I have just manually tracked all my targets using the the RA knob
on my EQ mount with occasional treak of the DEC. I have drives installed on
my SkyView Pro mount but I've only tested them....they track "OK"....

My question is, does the moon track at the same sidereal rate as do stellar
targets? Is the "path" the same or does it require different DEC settings
and/or tweaks?
What about the planets? Would Saturn stay within the FOV if I had an ideal
polar alignment?

Thank you for discussing....as for accuracy, I'm really only interested in
holding a target for 20-30 minutes----I'm not into photography but do share
my views with many people and it's very difficult to continually have to
adjust...

Doink.

[SaberScorpX]

My question is, does the moon track at the same sidereal rate as do >stellar

targets?

No. Some systems have separate tracking speeds for Luna.

What about the planets? Would Saturn stay within the FOV if I had an >ideal

polar alignment?

Yes. Sidereal tracking will work fine with planets (for your purpose).

Thank you for discussing....as for accuracy, I'm really only interested in
holding a target for 20-30 minutes----I'm not into photography but do >share

my views with many people and it's very difficult to continually >have to
adjust...

As a side note, I rarely use tracking during public shows. Usually I take a
quick look and tweak the RA for each new viewer specifically so they can watch
the object drift thru the field. More surreal than just looking at a stationary
target. All seem to enjoy it, especially with Luna as they get the feeling of
cruising over the features from above.

SSX

[Doink]

SSX,

Good tip. You're right now that I think about it because people ALWAYS
comment about how quickly things "move".
How close would "Normal" tracking be compared to the moon's rate? Within
20% or WAY off?

Doink

Post by Doink

Post by Doink
My question is, does the moon track at the same sidereal rate as do

Post by Doink
stellar

targets?
No. Some systems have separate tracking speeds for Luna.

Post by Doink
What about the planets? Would Saturn stay within the FOV if I had an

Post by Doink
ideal

polar alignment?
Yes. Sidereal tracking will work fine with planets (for your purpose).

Post by Doink
Thank you for discussing....as for accuracy, I'm really only interested in
holding a target for 20-30 minutes----I'm not into photography but do

Post by Doink
share

my views with many people and it's very difficult to continually >have to
adjust...
As a side note, I rarely use tracking during public shows. Usually I take a
quick look and tweak the RA for each new viewer specifically so they can watch
the object drift thru the field. More surreal than just looking at a stationary
target. All seem to enjoy it, especially with Luna as they get the feeling of
cruising over the features from above.
SSX

[SaberScorpX]

Post by Doink
How close would "Normal" tracking be compared to the moon's rate? Within
20% or WAY off?

Sidereal tracking basically just compensates for Earth's rotation against fixed
stars (about 15 deg.of RA per hour).
Lunar mode also takes into account the eastern progression of our moon
(about 30' per hour).
It's roughly a 3.3% difference.
Not a big deal for casual viewing.

SSX

[HAVRILIAK]

Post by SaberScorpX
Some systems have separate tracking speeds for Luna.

Mine has stellar, sun, moon and near the horizon where there are lens effects.
Its the G-11 tracking system. No planets though, probably because each plant
is different.

[Doink]

So does standard tracking have ANY value in lunar observing?

Post by HAVRILIAK

Post by SaberScorpX
Some systems have separate tracking speeds for Luna.

Mine has stellar, sun, moon and near the horizon where there are lens effects.
Its the G-11 tracking system. No planets though, probably because each plant
is different.

[Brian Tung]

Post by HAVRILIAK
Its the G-11 tracking system. No planets though, probably because each
plan[e]t is different.

I suspect it's because the planets are adequately tracked using the
sidereal speed. For example, Jupiter's motion differs from sidereal
motion by only arcminutes per day--not enough to affect observing or
even imaging.

The Moon, on the other hand, does move quickly--about 12 degrees per
day, on average--but its motion is so variable that you can't perfectly
accommodate it with a fixed-speed motor. What's more, there are also
refraction effects, which slow the apparent speed of all objects close
to the horizon.

Brian Tung <***@isi.edu>
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

[Rod Mollise]

Post by Doink
My question is, does the moon track at the same sidereal rate as do stellar
targets? Is the "path" the same or does it require different DEC settings

Hi:

The moon moves at a slightly differnent speed. It doesn't have anything to do
with dec, but with the speed of your RA motor. Some telescope drives do have a
Lunar rate.

But, for all practical purposes, even imaging, "sidereal" is more than good
enough. And that is for sure true with Saturn, who moves with agonizing
slowness.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto <http://members.aol.com/RMOLLISE/index.html>

[Mark Gingrich]

Post by Rod Mollise
The moon moves at a slightly differnent speed. It doesn't have anything
to do with dec, but with the speed of your RA motor. Some telescope drives
do have a Lunar rate.

Yes, the Moon's apparent speed relative to the background stars is
unrelated to declination, but the RA component of that motion indeed
depends on declination. And it's the RA component that defines the
instantaneous lunar rate.

Luna's orbital trajectory at high declinations results in a greater change
in RA. For one thing, the motion more closely parallels the celestial
equator; in addition, each degree of travel cuts across more lines of RA,
converging as they do toward the celestial poles. So if the other factors
(the apogee/perigee speed difference, refraction, topocentric parallax)
are ignored, instantaneous lunar rate at high declinations is always
slower (slower because that increased change in RA is in the direction
*opposite* the sky's diurnal motion) than at low declinations.

Alas, 'scope drive controls with a lunar-rate setting traditionally
employ a mean lunar rate, not an instantaneous lunar rate. But with
the embedded computing power in Go-To 'scopes nowadays, I'd think it's
not too difficult for manufacturers to implement an instantaneous lunar
rate.

[Rod Mollise]

Post by Mark Gingrich
I'd think it's
not too difficult for manufacturers to implement an instantaneous lunar
rate.

Hi Mark:

I wouldn't either. So why haven't they? Well, I don't know of an application
that really requires it, do you?

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto <http://members.aol.com/RMOLLISE/index.html>

[Mark Gingrich]

Post by Rod Mollise
I wouldn't either. So why haven't they? Well, I don't know of an application
that really requires it, do you?

A few applications spring to mind:

* When showing interesting lunar features (the Straight Wall, for example)
at public outreach events, 'tis best to employ high magnification and have
the target well-centered in the eyepiece. If the 'scope is tracking at
the instantaneous lunar rate, I needn't re-center the target nearly as
frequently.

* Instantaneous lunar rate makes it easier to capture a sharp image of
the Moon during a long time exposure of a very dark lunar eclipse.

* It likewise maintains better target registration, such as when attempting
a time-lapse video of a lunar eclipse, or a time-lapse close-up of the
rim shadow creeping across the crater floor of Copernicus, or recording
the nocturnal side of the Moon for possible flashes from meteor impacts,
or catching multiple events on the dark limb when the Moon occults the
Pleiades or the Beehive.

[justbeats]

Post by Rod Mollise
I wouldn't either. So why haven't they? Well, I don't know of an application
that really requires it, do you?

Add "taking automated high resolution mosaic through LRGB filters".

I found out when trying to re-register and combine the tiles that
drift in the normal sidereal setting is a real pain. Had to overlap
each tile by about 40% to get full coverage - which resulted in me
needing 30 x 4 exposures to cover the full moon (shooting at F/10). I
think I would have got away with 20 x 4 if drift hadn't been a factor.

Note: I have since discovered that I can set my scope to a lunar
tracking rate - and I will use this next time. So clearly, it IS
useful, but we are talking rather specialist uses here, so on balance,
I'm with Rod. From the manufacturers point of view, it's a pretty
spurious requirement.

Cheers
Beats

[Mark Gingrich]

Post by justbeats
Note: I have since discovered that I can set my scope to a lunar
tracking rate - and I will use this next time. So clearly, it IS
useful, but we are talking rather specialist uses here, so on balance,
I'm with Rod. From the manufacturers point of view, it's a pretty
spurious requirement.

I fail to see how accurate tracking of the sky's most popular telescopic
target is a "spurious" requirement, or how keeping a high-magnification
view of the Straight Wall well-centered over a longer stretch of time is
a "rather specialized use." A hundred years ago, some telescope mounts
came equipped with a lever to shift the drive gearing between sidereal
and mean lunar rate; I doubt that such a deliberate increase in mechanical
complexity was done for a spurious requirement.

With today's Go To 'scopes, an even better feature -- instantaneous lunar
rate -- could be had by modifying only the firmware, with a negligible
increase in the cost of goods. Heck, it would give the manufacturers yet
another thing to crow about in their advertisements.

[justbeats]

Post by Mark Gingrich
I fail to see how accurate tracking of the sky's most popular telescopic
target is a "spurious" requirement, or how keeping a high-magnification
view of the Straight Wall well-centered over a longer stretch of time is
a "rather specialized use." ...

When you put it like that, I have to agree with you.

So now I agree with everyone :-)