View this page "Techniques"

[cano...@yahoo.com]

I have created a stub page for the proposed page "Techniques". This
page is proposed to gather tips and techniques related to imaging the
ejecta cloud after impact and/or using features in Google Groups. The
second topic may be better placed under the FAQ. Comments on this
proposed page is welcome.

Click on http://groups.google.com/group/lcross_observation/web/techniques
- or copy & paste it into your browser's address bar if that doesn't
work.

[cano...@yahoo.com]

Added to Techniques page further explanations expanding on Dr.
Wooden's suggestion that the Horizon's telnet ephemeris interface can
be used to generate high-quality ephemeris data. See message:

Wooden 11-29-2008 message
http://groups.google.com/group/lcross_observation/msg/f8f62362f13251b2

A sample annotated Horizon's Telnet session by Kurt that illustrates
the techniques suggested by Dr. Wooden.
http://lcross_observation.googlegroups.com/web/20090215TelenetSessionExample.rtf

A sample Excel spreadsheet using geocentric ephemeris data for Fibiger
by Kurt in csv format generated in a Horizons' Telenet session. The
spreadsheet can be used to plan favorable observing times for Fibiger.
http://lcross_observation.googlegroups.com/web/20090215FibigerPlan.xls

- Clear Skies - Kurt

[Jim Mosher]

Kurt,

I suppose this is interesting work, but I'm unable to tell from you
message if your objective is the same as Dr. Wooden's, or something
different. She was primarily wanting to obtain the Right Ascension
and Declination of specific craters as seen projected in the sky from
her observing location. Is that what you are trying to find, too?

I hope my reply to her at:

http://groups.google.com/group/lcross_observation/browse_thread/thread/0415e18d31ae7a04/f8f62362f13251b2

didn't make you think this information was available only via the
Horizons telnet service. On the contrary, Dr. Wooden was pointing out
that (based on the Horizons tutorial page she cites) it's possible to
enter the coordinates of a specific point on the Moon in the normal
web interface. For those who require more advanced features, there
used to be an e-mail interface which most folks today would probably
find easier than telnet. As best I recall, you can send Horizons a
pre-cooked script of human-readable (ASCII) commands by e-mail, and
the system will send the requested ephemeris output (or a list of
problems encountered, if there are any) back to you a short time
later, also by e-mail.

I doubt that many lunar software packages output the RA and Dec of
individual craters primarily because most amateurs (and apparently
even Dr. Wooden herself, now) have found (unless perhaps you're
looking for something in the dark hemisphere) it's both simpler and
more accurate to point by crater-hopping. However, I believe the
Virtual Moon Atlas has a GoTo type telescope interface, so perhaps it
generates this kind of output, or at least can send the equivalent of
it to the drive motors. Likewise, LTVT can generate maps in an
equatorial or alt-az configuration, and the mouse readouts of the X
and Y offsets from the Moon's center can then be easily converted to
offsets in RA (X, in the equatorial mode) and Y (Dec) -- or Alt-Az for
that type of mount -- since X & Y are expressed as fractions of the
lunar radius, and the value of the current diameter (in arc-seconds)
is given.

If your interest is in making detailed predictions about when
particular target areas on the Moon will be visible from a particular
observing location on Earth, and what the lighting conditions will be,
I should think you would find the LTVT Libration Tabulator much easier
and more efficient to use:

http://ltvt.wikispaces.com/Libration+Tabulator

You simply enter your location and the feature you wish to observe and
it does the rest. The quantity of interest is really not the
libration in latitude or longitude, but how far the feature of
interest is from the Moon's apparent center. A feature with an offset
of 89.75 deg will be precisely on the limb as seen from Earth. One
with a lesser offset angle will be onto the visible disk by the amount
of the difference, and one with a larger offset will be on the
farside. The beauty of this parameter is that it applies equally well
to features at all latitudes.

Like Horizons, the LTVT Libration Tabulator can list the relevant
observing conditions (distance from Moon's center, altitude and
azimuth of Sun as seen from feature of interest, and positions of Sun
and Moon in the observer's sky) at fixed intervals (by checking "Show
All"), or it can condense the listing down by giving a single line for
each interval in which various criteria are met. A string of
observing opportunities lasting several nights is what you have been
calling a "nod". The accuracy is just as good as consulting Horizons
(since LTVT uses the same tables of JPL Moon, Sun and Earth
positions), and if that is the information you want, it seems a much
easier way to find it.

-- Jim

On Feb 15, 5:45 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> Added to Techniques page further explanations expanding on Dr.
> Wooden's suggestion that the Horizon's telnet ephemeris interface can
> be used to generate high-quality ephemeris data.  See message:
>

> Wooden 11-29-2008 messagehttp://groups.google.com/group/lcross_observation/msg/f8f62362f13251b2

>
> A sample annotated Horizon's Telnet session by Kurt that illustrates

> the techniques suggested by Dr. Wooden.http://lcross_observation.googlegroups.com/web/20090215TelenetSession...

>
> A sample Excel spreadsheet using geocentric ephemeris data for Fibiger
> by Kurt in csv format generated in a Horizons' Telenet session. The

> spreadsheet can be used to plan favorable observing times for Fibiger.http://lcross_observation.googlegroups.com/web/20090215FibigerPlan.xls

>
> - Clear Skies - Kurt
>

> Click onhttp://groups.google.com/group/lcross_observation/web/techniques

[Arnold Ashcraft]

Jim:
Under the ephemeris tab of Virtual Moon Atlas there is are figures
shown for RA and Dec, however they don't seem to change when you
center different areas of the moon. They may only indicate the
coordinates of the center point.
Clif

[cano...@yahoo.com]

The RA and Dec data is supplemental only. I have used your LTVT
Tabulator extensively. Although a worthy tool and outstanding
software, it misses observing opportunties and is difficult to
interpret into a useable observing list for this purpose. The
remainder of your questions are answered in my recent update to the
Librations in Latitude page. - Clear Skies - Kurt

On Feb 16, 4:40 pm, Jim Mosher <jimmos...@gmail.com> wrote:
> Kurt,
>
> I suppose this is interesting work, but I'm unable to tell from you
> message if your objective is the same as Dr. Wooden's, or something
> different.  She was primarily wanting to obtain the Right Ascension
> and Declination of specific craters as seen projected in the sky from
> her observing location.  Is that what you are trying to find, too?
>
> I hope my reply to her at:
>

> http://groups.google.com/group/lcross_observation/browse_thread/threa...

> > work.- Hide quoted text -
>
> - Show quoted text -

[cano...@yahoo.com]

Clif - That's because the libration value is for the whole disk of
Moon, not an individual feature on the disk. - Kurt

[cano...@yahoo.com]

P.S. - I invite you to prepare your own ephemeris of the 10 LCROSS
candidate targets for Feb. 15, 2009 through Sept. 30, 2009 using LTVT
and post the results here. - Clear skies - Kurt

On Feb 16, 4:40 pm, Jim Mosher <jimmos...@gmail.com> wrote:

> Kurt,
>
> I suppose this is interesting work, but I'm unable to tell from you
> message if your objective is the same as Dr. Wooden's, or something
> different.  She was primarily wanting to obtain the Right Ascension
> and Declination of specific craters as seen projected in the sky from
> her observing location.  Is that what you are trying to find, too?
>
> I hope my reply to her at:
>

> http://groups.google.com/group/lcross_observation/browse_thread/threa...

[Arnold Ashcraft]

I understand about the Libration. The ephemeris also gives RA and Dec.
That's what I was talking about. However, even if we had the RA and
Dec of a crater,
it would not mean much though, because it is constantly changing as
the whole
moon moves against the background of the sky.
Clif

[cano...@yahoo.com]

Cliff, Jim's comment about RA and DEC is collateral matter not worth
discussing that diverts from the main end product of the activity.
The main end product is a one page chart that easily fits in the
briefcase that summarizes six months of libration for LCROSS candidate
targets at both the north and south poles. Using the chart, you can
quickly estimate what poles to concentrate on nights between now and
impact for practice imaging that will have librations and
illuminations within the LCROSS mission parameters. If "final" impact
dates or targets change then the chart can used to quick plan what
similar librations are available for imaging opportunities. It is of
course a rough planning tool that should supplemented with additional
lunar planetarium tools such as LTVT and the LTVT calculator.

http://lcross_observation.googlegroups.com/web/20090216NorthSouthTargetPlan.jpg

Clear skies - Kurt

On Feb 16, 8:52 pm, Arnold Ashcraft <wa2...@optonline.net> wrote:
> I understand about the Libration.  The ephemeris also gives RA and Dec.
> That's what I was talking about.  However, even if we had the RA and  
> Dec of a crater,
> it would not mean much though, because it is constantly changing as  
> the whole
> moon moves against the background of the sky.
>                         Clif

> >> - Show quoted text -- Hide quoted text -

[Jim Mosher]

On 2/16/09, cano...@yahoo.com <cano...@yahoo.com> wrote:
> P.S. - I invite you to prepare your own ephemeris of the 10 LCROSS
> candidate targets for Feb. 15, 2009 through Sept. 30, 2009 using
> LTVT and post the results here.

As requested, I am attaching two lists of observing opportunities
during the whole of 2009 prepared using the LTVT Libration Tabulator.
For purposes of example, both are computed for Clif Ashcraft's
location in New Jersey. Other than knowing the coordinates of the
target one wishes to observe, no particular skill is needed to operate
the Libration Tabulator, so anyone else with access to a PC can
prepare a similar list for their own location.

To make these particular lists, LTVT was instructed to read the JPL
ephemeris at its default spacing of 5 minutes, and for each target, if
a time was found in which the observing circumstances met all the
criteria specified in the header, to print out the time during that
interval when the target was closest to the Moon's center. At this
time resolution, the complete evaluation of one observing target for
one year takes about 30 seconds on my 863 MHz Pentium III PC.

The first attachment uses the default Libration Tabulator settings to
list all observing opportunities in which the Moon would be above
Clif's horizon and the Sun below it. The second attachment imposes
the LCROSS scientists' restrictions that to make a useful observation
from Earth, the Moon must be at least 45 degrees above the horizon and
the Sun "two hours" (~30 degrees?) below it. Both these constraints
seem rather extreme to me. Many amateurs, drawing on their own
experience, will likely have different opinions as to where the Moon
and Sun must be for a useful observation, and they can plug in
whatever values they like and generate a corresponding observing list.

The further condition I have imposed that the Sun be at least
horizontal or above as viewed from the target position on the Moon is
also a somewhat arbitrary one. The outer walls of a raised feature
like Shackleton may be lit by the Sun even when it is a bit below that
level. Some experience is needed with the target being sought.

/from earlier in the thread/:

> I have used your LTVT Tabulator extensively. Although a worthy tool
> and outstanding software, it misses observing opportunties and is
> difficult to interpret into a useable observing list for this purpose.

Since the LTVT Libration Tabulator samples the observing conditions at
a user-selectable interval, I'm surprised to find it misses observing
opportunities. In the above examples, the sampling interval was 5
minutes, and the software should automatically locate any opportunity
that lasts that long or longer. If opportunities that last less than
5 minutes are sought, the sampling interval can be reduced at will.

I'm sorry that the output is so difficult to use and interpret. I've
added instructions for reading the tables in the attachments. The
value given for the target's "Center Distance" can be interpreted in
the same was as the "N" [nearside] flag in the Horizons output you
refer to. The value given for the Sun's altitude above the horizontal
as seen from the target is equivalent to, but more powerful than, the
"L" [lit] flag in your output. The other fields seem equally
self-explanatory to me, but perhaps they are not.

Reading down the first table in the first attachment we see, for
example, that from Clif's observatory the center of Nansen F reached a
minimum distance from disk center of 80.99 deg on Feb 12 (UT), but the
Sun was nearly horizontal and falling, so it would not have been in
sunlight the next day. A little further down, we see that on Mar 14
(UT) it might be possible to see the center of Nansen F 79.8 deg from
disk center in the early morning hours, again with the Sun setting
over the feature. On the mornings preceding this (back to Mar 7), it
is less close to the center, but more strongly lit.

Apparently you feel something has to be added to make this "a useable
observing list". Originally, I had planned to list not only the time
of minimum center distance ("maximum libration"), but also the start
and end times of each interval where the observer's criteria are met.
I rejected this because I thought it might be bit much, requiring
still more check boxes to activate or deactivate this "feature", but
perhaps it's still a good idea: due to the topocentric librations the
listed moment of minimum center distance tends to come at one end of
the interval or the other, which is perhaps a bit confusing, since
other times on the listed nights can be almost equally good.

-- Jim

[cano...@yahoo.com]

LTVT and the Tabulator is a great tool for what the name states that
it: Lunar Terminator Visualization Tool. It tells you when the
terminator is on observable and on the target. It is the premier tool
for this purpose. One that I use almost daily with great
appreciation.

What you did not design it to do, because it would not be reasonably
anticipated that anyone would have a need for it, was to prepare a
range of observing opportunities based on the illuminated fraction of
the disk. Thus, your raw unrestricted and restricted tabulations do
not clearly capture the needed answer to the problem - what are the
observable range of librations that are within the LCROSS 38% and 93%
illuminated fraction mission parameter. Granted that your unrestricted
ephemeris might be exported to a spreadsheet and supplemental
calculations performed to be able to drill down to the required data
set. But the LTVT Tabulator "center distance" constraint is not up to
that unusual and rare data selection task, nor would any reasonable
person expect it to be.

Using your first target on the individual observing point restricted
list for Region A in Nansen F, your restricted tabulation omits the
libration viewing and imaging opportunity between May 2 to May 5 - an
imaging opportunity frame that is within the LCROSS mission parameters
- albeit IMHO a poor choice if the LCROSS Team decided to use it.
Anyone reading this entry can confirm the above by loading up LTVT or
Virtual Moon Atlas and looking at the position of the terminator on or
about the indicated dates.

Your unrestricted viewing opporunity list does include ephemeris
entries for May 2 through May 6 - but indicates in the right hand
columns that the Moon is at an altitude of less than zero degrees
above observer's horizon. Conversely, it contains a few days, e.g.
9/22 to 9/24 where the illuminated fraction of the disk parameter are
exceeded, but that is a trival matter in this context for the question
under discussion.

Conversely, in JPL Horizons, it is possible to generate an observer
specific location ephemeris that directly captures both lunar altitude
above the observer's local horizon and illuminated fraction. My
generic geocentric spreadsheet was intended to target a broader range
of observers and I didnot prepare an example of an observer site
specific version, although instructions for that are provided.

Granted, you could gather ephemeris data for Nansen F, collect it into
a spreadsheet, compute the illuminated fraction and or the terminator
position and then do drill-down filtering.

It is however, a reasonable description to say that LTVT is not an
easy tool to use _for this specific problem_. "The purpose" being
identifying librations and illuminated fractions related to the LCROSS
mission and the _Call for images_ document. The JPL Horizon's system
is not easy to use for this purpose either; it is more difficult than
LTVT but gives more refined data. One can generate csv output from it,
as can be done with LTVT, and import it into a spreadsheet that one
can then drill-down to data that answers the proffered question.

Again, LTVT is a fine premire tool that everything one in the
community is appreciative of. I know you have hundreds of hours into
its development. The new LTVT_Tabulator version 0.0 added in late
2008 is a great addition that greatly added incremental features
beyond the existing Event Predictor v0.3. The Libration_Tabulator
feature is particularly useful for finding future occurrences when a
particular feature will be at nearly the same orientiation in
libration, so images of the same feature can be gathered under varying
illuminationsbut at nearly same orientation to an observer's camera.
If the LCROSS impact target, date and time were fixed instead of being
in a broad range of possible dates, times and locations, it would be
the ideal tool for the problem under discussion.

The answer to the postulated problem - how to find similar pre-event
libration observing windows in an environment of changing targets and
impact dates - is really benefited by export to a supplemental
spreadsheet - whether the source data comes from LTVT or Horizons -
for further drill-down filtering. That situation will change as the
target region (north or south), the specific target (one of the ten
current candidates or someother further target identified by LRO) and/
or impact date and time have more certainty.

Clear Skies - Kurt

On Feb 17, 10:13 am, Jim Mosher <jimmos...@gmail.com> wrote:

>  LibrationTabulator_2009ObservingOps_unrestricted.txt
> 172KViewDownload
>
>  LibrationTabulator_2009ObservingOps_with_LCROSS_ViewingRestrictions.txt
> 62KViewDownload- Hide quoted text -

[Jim Mosher]

Kurt,

Thanks for the many words of appreciation regarding LTVT.

--

> Using your first target on the individual observing point restricted
> list for Region A in Nansen F, your restricted tabulation omits the
> libration viewing and imaging opportunity between May 2 to May 5 - an
> imaging opportunity frame that is within the LCROSS mission parameters
> - albeit IMHO a poor choice if the LCROSS Team decided to use it.

The examples posted here were intended to illustrate how the LTVT
Libration Tabulator could be used, either with its default settings or
with customized settings, to provide a useful list of observing
opportunities. But like yours, the restrictions imposed here do not
quite properly capture the actual LCROSS ground-based observing
constraints, which were originally(?) expressed in terms of minimum
available hours of observation before/after dawn/dusk from a specific
site, with the Moon at or above a set altitude. See slides 28-37 near
the end of the Powerpoint presentation at:

http://lcross.arc.nasa.gov/docs/LCROSS_OverviewforObs.ppt

As you say, the peculiar way in which the LCROSS requirements are
stated requires a customized analysis that LTVT was not designed for.
I will try to provide printouts illustrating how the LCROSS
constraints work in a separate posting.

LTVT omits the particular instance you cite simply because of a
difference in the way we define a "viewing and imaging opportunity".
LTVT filters its list based on two parameters that seem useful to me:
(1) the altitude of the Moon above the observer's horizon and (2) the
altitude of the Sun above the observer's horizon. The first is
related to the air mass through which the Moon must be observed, and
the second to the sky darkness. The example you refer to was intended
to show how an observer can use these parameters to restrict the
output to instances meeting their personal observing preferences. The
values chosen asked that the Moon be 45 degrees above the horizon and
the Sun 30 degrees below: values that seemed similar to, but not
identical with, the restrictions LCROSS scientists have chosen to
require in their selection of possible impact dates. Your definition
of a viewing/imaging opportunity seems, I believe, to be that the
geocentric illuminated fraction of the Moon must be between 38 and 93%
without consideration of the altitudes of the Moon and Sun as seen
from an observing site.

As to whether LTVT made an error in the listing, the printout attached
to the present e-mail shows how the Libration Tabulator can be used in
its "Show All" mode to list the detailed observing circumstances for
Nansen F from Clif's location at a fixed interval over the limited
range of dates you mention, much like a JPL Horizons output, but
displaying quantities of more interest to the lunar observer. This is
essentially the data that the program evaluates automatically to
locate windows in which the specified criteria are met. Scanning
through the list, it can be seen that from May 1 through May 6, 2009
(UT), there are no occasions when the Moon (as seen from Clif's
observatory) was more than 45 deg above the horizon at the same time
the Sun was 30 deg or more below the horizon. As previously indicated
in the "unrestricted" printout, this does not mean there weren't many
other occasions on which a useful observation could be made. For
example on May 1 at 01:00 UT the printout indicates the center of
Nansen F would be well onto the visible disk (87.5 deg from disk
center), well lit (Sun 5.3 deg above horizontal at center of Nansen
F), with the Moon's center 52.7 deg above Clif's horizon, and the Sun
12 deg below it. 12 deg below the horizon gives a dark enough sky for
many lunar observing purposes, but this opportunity was correctly
rejected in the listing you refer to because the Sun did not meet the
requirement imposed there of being 30 or more degrees below the
horizon.

--

> Your unrestricted viewing opporunity list does include ephemeris
> entries for May 2 through May 6 - but indicates in the right hand
> columns that the Moon is at an altitude of less than zero degrees
> above observer's horizon.

The maximum librations often occur at moonrise or moonset, and because
the sampling was at intervals of five minutes, the precise moment of
moonrise/moonset was not necessarily captured, but lines with negative
lunar altitudes should not have been printed out unless the operator
specifically asked for them. Are you perhaps looking at the columns
listing the altitude of the Sun? The default Libration Tabulator
settings ask the computer to print out only times when the Moon's
center is at an altitude of zero or more. Where do you see a negative
lunar altitudes?

-- Jim