GRAZING OCCULTATION INSTRUCTIONS FOR YEAR 2007
International Occultation Timing Association, European Section
Dr. Eberhard Riedel Schuberstr. 7
D - 80336 Muenchen November 2003
GRAZEREG Version 2006 (GRAZREG5.EXE)
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The GRAZEREG 2006 program, that is now named 'GRAZREG5.EXE', was designed
to cross-reference between yearly grazing occultation binary data and any
ASCII file of station data to produce output files containing all grazing
occultation events for the specified observers within the given region
including profile plots. The use of former versions of GRAZEREG has become
obsolete with version 2006.
THE OUTPUT
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1. The observers heading
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The first two lines give the year of the calculation, and name, place,
geographic position of the observer and her/his travel radius.
2. Graze Overviews
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The prediction list for every single observer is preceded by a summary
list that gives an overview on all occultations within the observer's
travel radius. If graze events of bright stars outside of the observer's
travel radius are included, there is also a second overview list normally
showing all grazes of stars brighter or equal 4.5 mag. that occur within
the complete Super Standard Region. Sometimes though the limiting stellar
magnitude may be chosen brighter and/or the area covered may be decreased
to reduce the amount of data.
The column 'H/P/S#' contains the position source catalog number of the
star. If the number is preceeded by an 'H' it is the Hipparcos catalog,
'P' is a star from the PPM catalog and 'S' is a SAO-star. There is not
enough space for Tycho numbers in this column.
The percentage of the sunlit lunar surface is followed by a '+' for waxing
and '-' for waning phase. If the percentage is followed by an 'E' it gives
the fraction of the Moon's diameter outside of the umbra at time and loca-
tion of least distance to the observer's station. If the percentage is
followed by an 'N' the event occurs shortly before or after a lunar
eclipse 'N'ear the umbral shadow.
The column 'D(KM)' resp. 'D(MI) has the least distance to the graze path
in kilometers or miles, and the 'UT' refers to this very location of the
path.
In the column 'CUSP' the Cusp Angle is given as the absolute difference
between the position angle of the cusp and the position angle of graze.
The letter 'D' after the angle denotes a graze on the dark lunar limb,
the letter 'B' one on the bright side. 'T' marks a graze close to the
terminator of the geometrically dark lunar limb within 1 degree or less
of the geometrical terminator. For a graze during a lunar eclipse the
Cusp Angle is left away, so only the letters 'D' or 'B' show whether
the event is on the eclipsed or bright lunar limb.
3. The graze path prediction
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The heading for each graze shows three columns
named 'EVENT', 'STAR' and 'MOON'.
The field for the star number now generally first gives the number of the
catalog that was used as the position and proper motion source. The obser-
vers should be advised to only report this number to ILOC. Of course at
present this is not possible in all cases, but ILOC will hopefully change
the format real soon.
The format of the Tycho numbers (4 digits, 5 digits and 1 digit) leaves
leading zeros or blanks away in the output. The stellar magnitude is
'visual' unless followed by 'B' (B magnitude).
In case of a graze during a lunar eclipse no position angle of cusp is
given and the percentage of the sunlit Moon refers to the fraction of the
Moon's diameter outside of the umbra at time and location of least dis-
tance to the observer's station.
Latitude and Universal Time:
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The graze path coordinates and time values are corrected for the chosen
local geodetic datum and for refraction. The only possible offset of the
graze path is therefore caused by the lunar limb profile and by mostly
neglectable height differences of geoid ondulations of the International
Reference Spheriod. Longitude is now given in Degs. Min. and Sec.
rather than Degs. and Min. and tenths of a Minute.
These corrections make it possible to plot highly precise graze paths
into the maps available to the local observer. Small shifts may only
sometimes occur near the edges of a geodetic datum region due to some
overlapping areas.
Since the path values refer to mean sea level, the path has to be shif-
ted to the elevation of the observing site towards the lunar azimut
using TANZ.
Cusp Angle:
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The Cusp Angle and the letter describing the illumination of the lunar
limb (D, B or T) only show the geometrical situation. Thus a bright limb
event at crescent phases may very well occur on the dark limb and vice
versa. A better idea of the situation is provided by the profile predic-
tion.
A few grazes are included occurring on the bright limb with their central
graze angle (and are unobservable there) but have a possible event at a
different position angle where the Watts Data yield a mountain in dark-
ness so at least one dark limb disappearance and reappearance of the star
can be suspected.
The rightmost column in the graze path prediction has a 'T' in the head-
line and gives letters 'A', 'B' or 'C' for the required telescope aper-
ture. 'A' means 4-inch telescopes are sufficient, 'B' denotes apertures
up to 6 inches, and 'C' suggests telescopes well above 6 inches.
Lunar Eclipses:
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Instead of a Cusp Angle a value of the 'Umbral Distance' in degrees and
decimals is given. Umbral distance in this case means the distance of
the grazed star from the edge of the umbra, not from its center.The right-
most column gives a 'T' for 'total' when the moon is fully in the umbra
during midgraze, and 'P' for 'partial' when the graze is during a partial
eclipse phase. These events can be observed with small telescopes, so the
letter for the minimum telescope aperture is left away.
Sometimes a grazing event is given as an eclipse event in the heading, but
there is no lunar eclipse along the short portion of the graze line for
the specific observer. In this case the rightmost columns state 'NEAR',
meaning 'near the umbra', and the letter 'B' for 'bright limb' and the
letter for the recommended telescope aperture is given.
Used Geodetic Datum and Star Catalog:
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Directly following the graze path data the geodetic datum for the longi-
tude/latitude values and the used stellar catalog is stated.
Credit Line:
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Below that the GRAZEREG version number and the computor's name(s) are
given in a credit line.
4. Observer Scan
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All other observers within the same Super Standard Region, that have the
same event inside their travel radius are listed with their location and
distance and time of their closest approach.
5. Profile Plot
---------------
If requested, each graze path prediction within the observer's travel ra-
dius (not outside of it) is directly followed by the profile plot of that
event. It is always plotted for the location and time of the observer's
closest approach to the graze path, centering the corresponding position
angle of graze in the headline 'PA' and the central Watts angle in line
'WA'.
The mean lunar limb always agrees with the 0 km-line, which is the predic-
ted limit, at central graze, because the graze path data already includes
the shifts due to geodetic datum and refraction. The mean lunar limb is
plotted with the letters 'D' for the dark limb and 'B' for the bright
limb. During a lunar eclipse the dark mean lunar limb within the umbra is
denoted by the letter 'E'.
The terminator is shown with 'T's and is given at its geometrical posi-
tion for lunar phases between 21 degrees and 339 degrees. At crescent
phases the terminator is plotted at a decreased position angle allowing
for the retreat of the cusp. A 'Worst Terminator' is not included in the
plots, instead the letter 'W' stands for the worst case of lunar limb il-
lumination referring to possible mountains of a height of 2 arc seconds.
The worst limb is geometrically a dark limb and always starts where the
terminator hits the limb.
The lunar profile is continuously plotted with 'o's, 'x's and asterisks (*)
thus making use of three separate data sets:
- The Watts data (with corrections according to Yoshio Kubo, Tokyo) are
identified by an
'o'.
- All observed limb data formerly also given with ACLPPP are identified by
an
'x'.
- All observed limb data now published as MOONLIMB data are identified by
an
'*'.
The MOONLIMB data set represents the most complete and most precise compi-
lation of observed lunar profile from both total and grazing occultations
of the past, thus outperforming the ACLPPP data set in precision and size.
The MOONLIMB data was checked for consistency, so only the most reliable
data was adopted. Since MOONLIMB and ACLPPP use different approaches in
data evaluation both data sets should be considered.
When all of these three data sets are shown together in one profile the
plots sometimes look a little crowded. It is not always possible to connect
the profile points by a smooth line. Sometimes the coverage is so dense,
that with the poor resolution of the profile plots there is more than one
symbol of that limb data in one column, and sometimes there are wide gaps
in the observed data. Any connection between limb structures of different
symbols is not recommended though.
But even with a rough connection of the profile points there is a good
chance to estimate the favorable location for an observation. The observed
data ('*' and 'x') always has to have priority, and also is the only data
shown in the Cassini regions, where Watts data does not exist. It is not
recommended to connect two profile points with a larger gap of Axis Angle
between them by a straight line, since the unknow profile in between might
differ considerably.
The table below the profile gives the time and location for which the pro-
file is valid and the angles of libration used here. The 'VERTICAL SCALE'
value corresponds to the former VPS-value, but is calculated in a diffe-
rent way from the actual topographic situation. All corrections to obser-
ving locations derived from this value always have to be made perpendicu-
lar to the graze path heading (see value 'HEADING', which is the azimut
direction of the lunar motion on the earth's surface).
The value 'LUNAR VELOCITY' is equal to the former HPS-value and gives the
rate of lunar motion per minute relative to position angles on the lunar
limb.
Any graphic display of secondary or tertiary stars was left away to leave
an easy estimate to the observer using the separations and position angles
given in the path predictions.
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Eberhard Riedel