To calculate a visibility diagram:
Start Planetary, Lunar, and Stellar Visibility
. A visibility
diagram is calculated for the last selected object, year, and observer location (stored in pvis.ini). The vertical axis shows the date in months and days and the horizontal axis the time in 24 hours measured from midnight. The colors of the diagram show when the object is: visible above the horizon (shaded color corresponding to magnitude), above the horizon with the sun and thus invisible (light color), invisible due to low altitude (dark color) or below the horizon (black). (The moon of course is usually visible, and Venus sometimes visible, when above the horizon with the sun.) In the Settings
menu check mark dates of visibility phenomena
; horizontal lines show the dates of visibility phenomena and small vertical lines the times the object and the sun rise or set on those dates. In the Settings
menu check mark sunrise/sunset
; curved lines show the time of sunrise and sunset for every day. In the Settings
menu check show grid
; a grid shows the first day of each month and even numbered hours. Moving the cursor over the diagram shows, below the diagram, the date, time in intervals of 4 minutes, altitude and azimuth to 0.1 degree, and magnitude to 0.1 magnitude; for the moon, instead of magnitude the phase is given in percent illumination. Hold down the left mouse button, and lines for the date and time appear; moving the cursor then shows, below the diagram, the same information for (1) change of time with fixed date, (2) change of date with fixed time, (3) change of both time and date.
Each of the following selections begins a new calculation:
The following selections give additional information:
- Choose the object for the visibility diagram from the object list, which contains the sun, moon, nine planets, and stars, which in turn opens the list of stars. To run the calculation for a different star, select it and press calculate or double-click on the star.
- Choose the place of observation: Click the button place. A places window with a list of predefined locations appears. If the required location is in the list, select it and click OK; if not, see Selection of Location below. The eight locations last used are saved in a list activated by the arrow next to place and may be selected from the list. To apply daylight savings time rules for a predefined location, in the Settings menu check use daylight savings time (DST).
- Choose the year: Write the year in the field year and press Enter or click the arrow next to the object list; use arrows to move to the preceding or following year. If the current year is selected, for the selected location a cross marks the current date and time, which appear below the diagram in red with the object’s altitude and azimuth. Astronomical dating is used for years before AD 1, so for 1 BC enter 0, for 2 BC -1, for 100 BC -99, etc. (BC dates are automatically converted; thus if “2 BC” is entered, it is converted to -1.) Dates are in the Julian Calendar through 4 October 1582, and then in the Gregorian Calendar, which begins on 15 October 1582. (Compute for 1582, and you will see that 1. oct to 1. nov. is short.) Dates between -2999 and +6000 are accepted although calculations for more than ±2,500 years from the current epoch become increasingly less secure.
- In the Settings menu, check show dates of visibility phenomena. For the planets Mercury, Venus, Mars, Jupiter, Saturn, and the stars a heliacal dates window opens showing the dates of visibility phenomena with the times of object rise or set and sun rise or set associated with the visibility, the time in hours between object rise/set and sun rise/set, the “age” of the phenomenon at the time of object rise/set in days and hours before or after true conjunction or opposition, and the magnitude of the planet or star. Object rise/set is, not necessarily the time the body crosses the true horizon, but the time it reaches the least altitude at which it is visible, here called the critical altitude.
For the moon, a first and last visibility of the moon window opens showing the dates of first and last visibility, times of sun rise or set and moon rise or set associated with the visibility, the time in hours between sun rise/set and moon rise/set, the phase of the moon in percent illumination, the “age” of the moon at the time of sun rise/set in hours before or after true conjunction, and the length of the preceding true lunar month, 29 or 30 days, between successive first visibilities. Click on text/print; an edit text window opens containing the information, which can be edited, saved as an .rtf file, printed, and pasted into other documents. As long as the program is running, the edit text window accumulates the information in a single file each time text/print is clicked. One can, for example, accumulate information on all the planets for a single year or on a single planet for a number of years.
- In the heliacal dates window, click more information. The window then gives additional information, all to minutes of arc: for the planets and stars, for the time of object rise/set (at critical altitude): (negative) altitude and longitude of the sun, longitude, latitude, and magnitude of the planet or star, difference of azimuth and of longitude of the object and sun; for the moon, for the time of sun rise/set: longitude of the sun, longitude, latitude, altitude, and phase of the moon, difference of azimuth and of longitude of the moon and sun. The command text/print and the edit text window are as described above.
- In the File menu, select Rise and set times (HTML).... In the Rise and set times dialog, click OK and an HTML file is calculated containing the rise, culmination, and set times of the sun and the selected object for each day of the selected year. To compute the differences in time between the object and the sun, check calculate differences; to compute for less than one year, select the quarter or month from the drop-down list of the time span.
- In the File menu, select Dates of visibility phenomena (HTML).... In the Visibility phenomena dialog, select the number of years to be computed and the interval between the years. Click OK and an HTML file is calculated for the selected number and interval of years with the information contained in 4. To include the information in 5, check more information.
- In the Settings menu, check show object rotation/illumination. A rotation/illumination window opens showing the rotation, inclination, illumination, and variation of apparent size of the object. Move the cursor over the visibility diagram and the rotation, inclination, illumination, and apparent size of the body are shown for the selected date and time along with other information. Moving the cursor horizontally shows principally rotation; moving the cursor vertically shows principally change of inclination, illumination and apparent size.
- In the object list, select sun or moon. When the calculation is complete, in the Settings menu check mark eclipses; a short horizontal line, if present, shows the date and time of any solar or lunar eclipses in the year visible from the selected location. Move the cursor over the line and an eclipse window opens showing the eclipse. Move the pointer below the eclipse diagram and the moon moves over the sun in a solar eclipse, or through the earth’s shadow in a lunar eclipse, and for the time in UT, the eclipsed fraction in percent, direction of motion, and other information are shown. If the moon rises or sets during the eclipse, a horizon line crosses the diagram. Once the pointer is moved slightly, the right or down arrows on the keyboard move the body forward and the left or up arrows backward through the eclipse.
- In the object list, select Jupiter for year 1600 or later. When the calculation is complete, right-click near any date in the visibility diagram. The window Jupiter’s satellites opens showing the paths of the four Galilean satellites for some number of days before and after that date. Or, checking show Jupiter’s satellites in the Settings menu shows the beginning of the year; unchecking closes the window. The up arrow in the window reduces the number of days and increases the intervals of time within each day; the down arrow increases the number of days and reduces the intervals of time within each day. Moving the cursor vertically over the satellites diagram shows, below the diagram, the movement of the satellites on either side of Jupiter with the date and time in UT below the diagram, the least interval of time is 10 minutes, the greatest interval is 2 hours. The numbers at the bottom of the window, selected by the arrow, show the directions and distances of the satellites from Jupiter in diameters of Jupiter or in arc minutes, the diameter of Jupiter in seconds, all to 0.01 units, and more detailed information which can be selected for the individual satellites.
To Save or Print any Window
: Click on the window to make it active; press alt+print
(or alt+print screen
), which saves the window to the clipboard. It may then be pasted into any word or graphic document to be edited, saved or printed.
the program, click exit in the File
menu or the close box. All settings are stored in the initialization file (pvis.ini) and return the next time the program is started.