------------------------------------------------------------------------------- E X P L A N A T O R Y S U P P L E M E N T A quick guide to EclipseView and the on-screen data display John Irwin, 29 November 2015 ------------------------------------------------------------------------------- EclipseView is an interactive 3D planetary geometry viewer specifically for the visualisation of shadow cone intersections between Solar-System bodies. The classical example of this phenomenon is a solar eclipse in which the shadow of the Moon, cast by the Sun, sweeps across the surface of the Earth. EclipseView was originally created for solar eclipse viewing but, of course, the principal is the same for any three bodies for which ephemeris data are available, including cases where none of the bodies are actual emitters of light. Thus it is possible to simulate "shadows" associated with all kinds of transits and occultations, as well as eclipses. Being interactive, it is possible to animate the event in user-selectable UTC increments and watch the umbral and penumbral intersections evolve over time. The umbral and penumbral outline curves, as well as the intersections of the shadow-axis, are determined directly from the loaded object ephemerides. This applies to any three-body alignment but for Earth-based solar eclipses polynomial Besselian elements are also calculated on-the-fly from the chosen ephemeris basis. From these elements eclipse coverage maps can then be calculated and displayed. The elements are also used to determine local circumstances interactively for any location on the surface of the Earth. However, for any three-body alignment, instantaneous Besselian elements can be calculated from the loaded ephemeris basis and displayed alongside a view of the Fundamental Plane reference frame at the currently selected time. Also displayed are the penumbral and umbral shadow cones where they intersect the Fundamental Plane (whose radii correspond to the elements l1 & l2), together with the shadow axis intersection point (whose coordinates correspond to the elements X & Y). DISCLAIMER: The precision of the displayed data is not indictative of the accuracy of the prediction of eclipse events. However, for Earth-based solar eclipses, accuracies at the level of seconds in time and at the level of arcseconds in geodetic position are possible for events within the present UTC era (approximately from 1962 to a few months after the last EOP update). Outside the UTC era accuracy depends very much on the delta-T model in use. ------------------------------------------------------------------------------- EMT: Emitter - the celestial object representing the light source for the shadow; with valid ephemeris indicator ("+/-"). OCC: Occluder - the celestial object generating the shadow; with valid ephemeris indicator ("+/-"). REC: Receiver - the celestial object receiving the shadow; with valid ephemeris indicator ("+/-"). ------------------------------------------------------------------------------- EMT: Ephemeris source of the Emitter. OCC: Ephemeris source of the Occluder. REC: Ephemeris source of the Receiver. ------------------------------------------------------------------------------- EOM: Body orientation model of the Emitter. OOM: Body orientation model of the Occluder. ROM: Body orientation model of the Receiver. ------------------------------------------------------------------------------- OPC: Occluder position correction. EMR: Emitter radius - to indicate which ellipsoidal radius is used in the spherical approximation of the Emitter object; selectable between "long", "mean", and "short". OCR: Occluder radius - to indicate which ellipsoidal radius is used in the spherical approximation of the Occluder object; selectable between "long", "mean", and "short". PLC: Place reduction method; selectable between "Geometric", "Astrometric", and "Proper", the latter with ("rel") and without ("nwt") relativistic corrections). ------------------------------------------------------------------------------- LUN: Lunation Number of the currently displayed eclipse (displayed for Earth-based solar and lunar eclipses only). SAR: Saros Number of the currently displayed eclipse (displayed for Earth-based solar and lunar eclipses only). INX: Inex Number of the currently displayed eclipse (displayed for Earth-based solar and lunar eclipses only). ------------------------------------------------------------------------------- UTC: Current Receiver UTC, with Gregorian/Julian indicator "[G/J]", and UTC increment; selectable UTC to any value with 100 microseconds precision; selectable UTC increment between 0.0001 seconds and 100 Julian years; outside UTC era, UTC = UT1. UT1: Current UT1 of above, with Gregorian/Julian indicator "[G/J]"; outside UTC era, UT1 = UTC. TT: Current TT of above, with Gregorian/Julian indicator "[G/J]". ------------------------------------------------------------------------------- TT-UT1: Delta-T at the current UTC; outside UTC era, determined from model. UT1-UTC: Delta-UT at the current UTC; zero outside UTC era. Earth LT: Light travel time between centre of receiver and centre of the Earth in minutes. Time difference between UTC at the receiver and at the Earth. ------------------------------------------------------------------------------- SAI: Shadow-axis intersection point; planetodetic longitude and latitude (not displayed if axis does not intersect Receiver). SAR: Rate of above; degrees per second (not displayed if axis does not intersect Receiver). SAS: Surface speed of intersection point, kilometres per second (not displayed if axis does not intersect Receiver). UAD: Umbral Apex Distance - measured along the shadow axis from the SAI (not displayed if axis does not intersect Receiver). SAN: Point on the Receiver nearest the shadow-axis; planetodetic longitude and latitude (not displayed if axis intersects Receiver). SAA: Altitude of above; in kilometres (not displayed if axis intersects Receiver). ------------------------------------------------------------------------------- ECL: Type and date of current solar eclipse (displayed for Earth-based solar eclipses only). LCX: Local event data for the position at the centre-of-view, showing the UTC for each of the principal contacts and maximum eclipse, together with the sign of the Sun’s altitude at the time of each event (displayed for Earth-based solar eclipses only). ------------------------------------------------------------------------------- UMD: Umbral duration as seen from the position at the centre-of-view (displayed for Earth-based solar eclipses only). PND: Penumbral duration as seen from the position at the centre-of-view (displayed for Earth-based solar eclipses only). MGR: Magnitude and Ratio-of-Diameters at the time of maximum eclipse for the position at the centre-of-view (displayed for Earth-based solar eclipses only). ------------------------------------------------------------------------------- TGT: Planetodetic longitude and latitude of the centre-of-view; selectable to any position on the Receiver in "User" lock mode. Whatever the position and whatever the lock mode, the view is always directed to the centre of the Receiver. LCK: Current Lock mode; selectable between "User", "Shadow axis", "Sub-solar point", and "Fundamental plane axis". The view is fixed on the indicated position even if the position moves while animating. Useful for following the shadow-axis intersection as it moves across the Receiver. ------------------------------------------------------------------------------- FOV: Horizontal and vertical fields-of-view; selectable to any value between 120 degrees and 3 arcminutes. SCL: View Scale on the Receiver at the centre-of-view; in kilometres per pixel. ------------------------------------------------------------------------------- The data items displayed with the Fundamental Plane coordinate system are the instantaneous Besselian elements and their rates per hour, determined directly from the planetary ephemerides and orientation models: FPX: X-coordinate of the Occluder in the Fundamental Plane frame. FPY: Y-coordinate of the Occluder in the Fundamental Plane frame. FPZ: Z-coordinate of the Occluder in the Fundamental Plane frame. FPR: The distance of the shadow-axis intersection point on the Fundamental Plane from the centre of the Receiver; in units of the Receiver's long axis. FPM: "Greenwich Hour Angle" of the shadow-axis relative to the Receiver-fixed frame; in degrees. If the Receiver is the Earth, the Ephemeris Hour Angle is shown in place of the "GHA". FPD: "Declination" of the shadow-axis relative to the Receiver-fixed frame; in degrees. FL1: Radius of the penumbral shadow cone intersection with the Fundamental Plane; in units of the Receiver's long axis. FL2: Radius of the umbral shadow cone intersection with the Fundamental Plane; in units of the Receiver's long axis. TF1: Tangent of the generating angle of the penumbral shadow cone. TF2: Tangent of the generating angle of the umbral shadow cone. XI: X-coordinate of the centre-of-view in the Fundamental Plane frame. ETA: Y-coordinate of the centre-of-view in the Fundamental Plane frame. ZTA: Z-coordinate of the centre-of-view in the Fundamental Plane frame. RHO: Radius of the centre-of-view from the centre of the Receiver. -------------------------------------------------------------------------------