Observer Location

When SkyView first starts, the default view shows the Time menu on the left, a Sky Map plot in the center and a listing the sun’s location on the right.

The observer location will default to Perth when it is first started up after installing. A new observer location can be selected by  clicking on the "Obs Location" button. This will bring up an "Observer Location" window. To change the observer location. either click on the map, or type in new values of the latitude and longitude.

A list of changeable parameters can be found under Views->Parameters.

 

The view of the sky that is displayed is that which would viewed from the currently selected Observer Location at the date and time that has been selected. The Time Zone setting is defined by the Observer location.

The values of year, month, day, hour, minute and seconds can be incremented by clicking on the arrows either side of the value for these items. By default, they will increment in steps of 1 unit but the increment for each can be changed by using the corresponding increment slider.

The arrows next to the date/time values can held pressed down to show a continuous update. An application for this, for example, would be to set the current time to one hour after sunrise, then hold down the “day” arrow, to observe how the sun rise location moves daily.

The “Automatic update” button allows the software to run un-attended. There are 2 parameters associated with Automatic Update, and they are selected from the underlying drop-down menu’s. The first parameter is the “plot interval”, which is the time difference between the successive plots. The default is real-time, which means the plotting time is taken from the PC clock and updated very second. All the other options take the time from the manually selected values. The values of increment sliders are also considered, as the plot time is recomputed. The second parameter is the plotting refresh interval.

  

Sky Map plot

The Sky Map plot has a light blue background during the day time (when the sun is in the sky), and a light grey background during night time.

Clicking on an object on the Sky Map will do several things; (a) a red circle will appear around the object. Re-clicking on the object will remove the circle; (b) the listing will change to show information from the selected object, and (c) a Star Chart view will become centered on the selected object. If later the time is changed, the Star Chart will continue to stay centered on the selected object. The Star Chart will also follow the objects below the horizon. When region of the sky being viewed is below the horizon, the background becomes a light pink colour.

If the “shift key” is depressed when clicking on the Sky Map plot, then the Alt-Azim is selected instead of an object and the Star Chart will then stay locked onto the selected value of Alt-Azim, and will not follow any objects as the time is changed.

Clicking on the name of a star in the listing window will result in a small red circle to appear around that star. If the star was below the horizon when selected, then you’d have to advance the time until that star rises before it can be seen. Re-clicking on the star name will cause the red circle to disappear.

Checking the box labelled “Automatically flip to Star Chart”, will cause the Star Chart page to come up automatically if a star is selected either on the Star Map or from the selection list.

Clicking on the star name in the selection list whilst the “shift key” is depressed will rotate the sky until that star is at the meridian. That is, the time is changed so that the hour angle for that star is 360 degree. Be aware that there will be stars that will never be visible in the sky from your current viewing latitude (those that have a declination greater than negative value of your latitude). If you do want to view these stars, then select a latitude from the opposite hemisphere.

When clicking on a double star, the star selected may appear to be randomly one of either of the two components (assuming both components have a magnitude greater than the plot magnitudes). However, both stars will have slightly different locations in the catalogue, and clicking to one side of the star will consistently select the component that is to that side. For example,  Centaurus is a double star and clicking to the Centaurus side of  Centaurus will select the 1 component (Rigel Centaurus), and clicking on the other side will selected the  component.

The Auto Rotate options shown on the Star Chart will rotate the Star Chart such that the horizon is at the bottom and the will be directly above the centre of the plot. The other angles are fixed relative to the N, E, S & W directions; for example, a value of 90 means that the Easterly horizon is in the same direction as the lower edge of the plot.

 

Sky Chart plot

The Sky Chart plot has a light blue background during the day time (when the sun is in the sky), and a light grey background during night time. The Sky Chart can see the entire sky and when the view-able area is below the horizon, the background is colored light pink. There is an option to turn off the background coloring.

A single click on a star and the chart will rotate to place that star in the centre of the display. By default, the horizon line will stay level, so the display will appear to rotate. A level horizon also means the zenith will either be on a vertical line that goes through the center of the chart, or vertically above the centre of the chart.

Also upon clicking on a star, a red marker will be placed at that star, and the Star List will be updated to that star.

As time is advanced, the display will stay centered on the selected star, and by default, the display will rotate to keep the horizon line level.

Rotating the Mouse Wheel, will zoom in/out on the display.

Holding the shift key down while clicking on a star, and only a red marker is added and the listing updated for that star (the display will not rotate).

Holding the control key down whilst moving the mouse over the Sky Chart (without clicking), and a pop-up with red text text will appear giving information on the star nearest to the mouse cursor.

Clicking on an object in the Sky Map, or on a star name in the list on the right side of ther main form, will cause Sky Chart to come to the front and the object to be centered in the Star Chart.

If an object in the Sky Map is clicked while the Shift key is held down, the resulting Sky Chart display will stay fixed at the selected Altitude-Azimuth, and not move as time is advanced.

An option is available for Un-docking the Sky Chart. This allows to see a larger version, and also to see the SkyMap and Sky Chart simultaneously.

A scroll bar in the orientation box is used to rotate the Sky Chart when a fixed angle value has been selected.

 

Object Coordinate Data

The coordinates of the Sun, Moon and Planets are initially computed in geocentric ecliptic coordinates. These are transformed to geocentric equatorial coordinates, and finally to topocentric equatorial and horizontal coordinates.

Topocentric coordinates are corrected to the observers location on the Earth's surface. The topocentric correction is largest for nearby objects such as the moon, and very small for the far planets.

The "apparent" coordinate have atmospheric refraction corrections applied, which will show a notable difference only when the object is very close to the horizon. When an object is below the horizon, refraction correction has no meaning and is not applied.

Examples are shown below for Jupiter on 23rd and 24th Feb-2019. The first list is at 15:55 local time when Jupiter is below the horizon and is therefore un-observable, so the topocentric coordinates are shown in gray font. Later at 2:56 on the next day, Jupiter is above the horizon and the topocentric coordinates are in black font.

Stars coordinates are derived from a database of Equatorial coordinates. Different types of corrections are required and applied for objects outside of the solar system, and these are discussed later.

 

 

Solar plots and data

Clicking on the "Sun" button in the top menu brings up a window showing the Sunrise and Sunset times.

There are 4 other displays that are accessible from this window that include Solstice/Equinox date and times for the current year, Solar Analemma at the current location, the Equation of time plot and an Almanac listing of the sunrise, sunset and meridian transit times for the current year. 

 

Lunar plots and data

Clicking on the "Moon" button in the top menu brings up a window showing the Moonrise and Moonset times.

There are 3 other displays that are accessible from this window that include Moon Phases for the current year, Perigee and Apogee for the current year, and an Almanac listing of the moonrise, moonset and meridian transit times for the current year.

It is possible to toggle between the Sun and Moon windows without returning back to the main window.