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<TITLE>ObsReduce 1.3</TITLE>
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<H1 ALIGN=center>ObsReduce 1.3</H1>
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<H2 ALIGN=center>(C) 2003-05 by Ted Molczan. All Rights Reserved.</H2>
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<H2 ALIGN=center>2005 August 17</H2>
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<a href="#Intro">A. Introduction</a>
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<a href="#Eyepiece">B. Observations Are Made at The Eyepiece!</a>
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<a href="#Ops">C. Program Operation</a>
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<a href="#Interface">D. Description of User Interface</a>
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<a href="#Acknowledgements">E. Acknowledgements</a>
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<a href="#Install">F. Installation</a>
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<H3><a name="Intro">A. Introduction</H3>
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ObsReduce is an MS Windows program that reduces observations of satellites relative to the background stars into their precise coordinates. Observers identify their reference stars in a simulated binocular or telescope field of view, select them using the mouse, enter the observed geometric and positional data, and the program automatically produces a formatted observation report.
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ObsReduce supports three traditional observational geometries: satellite in-line with reference stars, satellite forming right-angled triangle with reference stars, and appulses (satellite passing near a single star).
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Observations in the form of images recorded by cameras may be reduced using two geometries: satellite located to the right or left of a pair of stars, or any configuration of a satellite and three stars. The user enters the pixel coordinates of the satellite and reference stars, or the measured lengths between them, obtained independent of ObsReduce.
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ObsReduce supports all three reporting formats in common use:
<a href="http://www.satobs.org/position/IODformat.html">IOD</a>,
<a href="http://www.satobs.org/position/UKformat.html">UK</a> and
<a href="http://www.satobs.org/position/RDEformat.html">RDE</a> (Russell Eberst's abbreviated form of the UK format.) All R.A. and Dec formats and epochs are supported, as are visual magnitude and optical period reporting.
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Several star databases, derived from the Tycho 2 catalogue, are available for ObsReduce. The magnitude 8.5 database, includes nearly 72,000 stars, The magnitude 10.5 database includes more than 540,000 stars. The magnitude 12.0 database includes more than 2 million stars. The complete set of Tycho 2 stars is also available, consisting of more than 2.5 million stars, to about magnitude 13. The star data bases range in size from 1.0 MB to 30 MB. ObsReduce enables the addition of stars missing from the database, as well as coordinates of planets and asteroids.
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The star databases store Epoch 2000.0 coordinates, proper motion and visual magnitude. About 4 percent of the stars in Tycho 2 do not have proper motion data, and though they are Equinox 2000.0, their epoch is c.1991. I hope to eventually provide data from alternative sources for many of those stars. Where available, ObsReduce makes use of proper motion in the reduction of observations, though it rarely materially affects accuracy.
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To aid in finding and confirming reference stars used in observations, ObsReduce has the ability to display predicted satellite tracks computed using the SGP4 and SDP4 orbital models. It also displays the difference between the satellite's predicted and observed time and track, and can compensate for Earth's rotation in the interim, to produce accurate plots of satellite tracks.
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ObsReduce can be configured to simultaneously write its results to as many as four text files. One file logs only the IOD, UK or RDE formatted observations. Another logs the underlying details of each observation: the position and magnitude of reference stars, the observational geometry, and the orbital elements used to locate the reference stars. The remaining two files are single session versions of these file types.
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ObsReduce provides numerous configuration options. For example, default values for site code, time uncertainty, position uncertainty, and the number of significant decimal points to be reported, can all be set via an easily editable initialization file. Many of the default settings may be readily changed on a per observation basis at run time.
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<H3><a name="Eyepiece">B. Observations Are Made at The Eyepiece!</H3>
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ObsReduce accurately plots a satellite's predicted track, and reports cross-track and time differences between prediction and observation - helpful in finding and confirming the reference stars used in an observation.
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One pitfall to be avoided is attempting to "improve" observations on the basis of the predicted track or the cross-track and time differences between prediction and observation. Observations are made at the eyepiece, and cannot be improved afterward, by ObsReduce or any other means.
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Differences between prediction and observation are to be expected - indeed they are the reason that we observe - to provide the data by which ever changing orbital elements may be updated. Attempting to "correct out" the differences obliterates the very data that we seek to obtain.
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So, please, use the satellite tracks to help locate your reference stars, but do not alter your observation to match them!
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<H3><a name="Ops">C. Program Operation</H3>
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ObsReduce may be used <a href="#C.1">with</a> or <a href="#C.2">without</a> the orbital elements of the observed object. It also facilitates making observations <a href="#C.3">without having to stop to sketch reference stars.</a>
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<B><a name="C.1">C.1 Using ObsReduce With Existing Orbital Elements</B>
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ObsReduce assists in locating the reference stars used in an observation, by using the object's existing elements to plot its track through a simulation of the observer's FOV (field of view) at the time of the observation.
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Since the vast majority of positional observations are made for the purpose of updating existing orbital elements, this feature will be useful most of the time.
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For the greatest ease of use, always use the most recent orbital elements available. Sources of orbital elements are listed <a href="http://www.satobs.org/tletools.html#two">here</a>. To find your elements file, ObsReduce follows the path and name entered at line 33 of the ObsReduce.ini file.
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If the object was nearly on time (i.e. difference between its observed and predicted position was within the radius of the observer's field of view), follow the steps in <a href="#C.1.1">Section C.1.1</a>.
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If the object was significantly early or late (i.e. the difference between its observed and predicted position exceeded the radius of the observer's field of view), but the time difference is accurately known, then follow the steps in <a href="#C.1.1">Section C.1.1</a>.
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If the time difference is not accurately known, but the approximate R.A. and Dec of the reference stars is known, then follow the steps in <a href="#C.1.2">Section C.1.2</a>, else, if the location of the stars is not known, but you have a good sketch of them and a few surrounding stars in the field of view, then follow the steps in <a href="#C.1.3">Section C.1.3</a>.
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<B><a name="C.1.1">C.1.1 Satellite Passed Nearly On-Time Or Time Difference Known</B>
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If the difference between the object's observed and predicted position was within the radius of the observer's FOV (field of view), or the duration by which it was early or late is known, then perform the reduction as follows:
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- select <a href="#Site">observation site</a>
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- enter <a href="#Desig">Desig</a> and/or <a href="#SSN">SSN</a>
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- IOD users select site <a href="#Status">Status</a>
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- enter <a href="#Date&Time">date and time</a> of observation
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- if the object was on-time, enter zero in <a href="#Early/Late">Satellite Early / Late</a> text box, else enter the amount by which it was early or late
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- press <a href="#Plot">Plot Satellite</a> button
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- <a href="#Select">select the displayed reference star(s).</a> ObsReduce displays the stars and the satellite's track in the FOV, oriented as they appeared at the time of observation. The more accurate the orbital elements, the closer the reference star(s) will be to the centre of the FOV.
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- select the <a href="#Geometry">geometry</a> of the observation and enter the object's position relative the reference star(s)
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- if they were observed, enter the object's <a href="#Magnitude">magnitude</a> (brightness), <a href="#Period">period of variation</a> and <a href="#OpticalCode">optical code</a>
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- press the <a href="#Reduce">Reduce</a> button
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- briefly review the <a href="#Error">Obs - Pred</a> information. If the cross-track and/or time difference seem unreasonable, then you should review to make certain that you entered the correct data and selected the correct stars.
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- if the observation minus prediction time difference is sufficiently large that your reference stars are noticeably displaced from the centre of the FOV, then you can centre them, and those of any other observations of the same object, by pressing the <a href="#UseAs">Use As Early/Late button.</a> This has the effect of instantly updating the FOV display, and copying the prediction time difference into the <a href="#Early/Late">Satellite Early/Late text box.</a>
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- you may save your observation using the <a href="#Save">Save button</a> near the lower right corner of the program's window. If you wish to discard it, press the <a href="#Clear">Clear Position button.</a>
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- if you have additional observations of the same object, then repeat the steps in this section, beginning with the date and time. The last date and time will still be there, so you need only edit it as required.
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<B><a name="C.1.2">C.1.2 Reference Star Coordinates Known</B>
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If the object was significantly early or late, by an unknown duration, but you know the coordinates of your reference stars, then follow these steps to bring the object and the reference stars into the FOV:
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- select <a href="#Site">observation site</a>
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- enter <a href="#Desig">Desig</a> and/or <a href="#SSN">SSN</a>
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- IOD users select site <a href="#Status">Status</a>
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- enter <a href="#Date&Time">date and time</a> of observation
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- enter zero in <a href="#Early/Late">Satellite Early / Late</a> text box
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- press <a href="#Plot">Plot Satellite</a> button. The satellite will be in the wrong place, but this step is required to load its elements.
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- in the <a href="#Centre">FOV Centre</a> frame (at lower right of the FOV), enter the RA and Dec (or the AZ and EL) approximately centred on the reference stars. The satellite's track will disappear, but your reference stars should now be visible in the FOV.
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- <a href="#Select">select the displayed reference star(s)</a>
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- select the <a href="#Geometry">geometry</a> of the observation and enter the object's position relative the reference star(s)
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- if they were observed, enter the object's <a href="#Magnitude">magnitude</a> (brightness), <a href="#Period">period of variation</a> and <a href="#OpticalCode">optical code</a>
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- press the <a href="#Reduce">Reduce</a> button
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- briefly review the <a href="#Error">Obs - Pred</a> information. These differences have been computed relative to the object's orbital elements loaded earlier. The time difference is an accurate measurement of how early or late the object was relative your observation. The position cross-track difference should be fairly small, because the track has been compensated for Earth's rotation corresponding to the time difference.
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- now that the difference between the observed and predicted time is known, it can be used to easily find the reference stars of any additional observations of the same object still to be reduced, Simply press the <a href="#UseAs">Use As Early/Late button.</a> This has the effect of instantly updating the FOV display, and copying the prediction time difference into the "Satellite Early/Late text box.
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- you may save your observation using the <a href="#Save">Save button</a> near the lower right corner of the program's window. If you wish to discard it, press the Clear Position button.
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- to begin reducing another observation of the same object, edit the date and time. Do not change the value in the Satellite Early/Late box. Press Plot Satellite, which will display your new reference stars, and the satellite's track. From here, the reduction proceeds as any other reduction.
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<B><a name="C.1.3">C.1.3 Reference Star Coordinates Not Known</B>
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If the object was significantly early or late, by an unknown duration, and you do not know the coordinates of your reference stars, but have a sketch of them, then follow these steps to bring the object and the reference stars into the FOV:
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- select <a href="#Site">observation site</a>
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- enter <a href="#Desig">Desig</a> and/or <a href="#SSN">SSN</a>
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- IOD users select site <a href="#Status">Status</a>
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