21.0 Setting and controlling location
RedShift lets you set your location anywhere, relative to any object in the Solar System, or anywhere in space within the Solar System (within 9,999 astronomical units of the Sun). RedShift provides pre-set options for setting your location relative to an object.
By default, RedShift sets your initial location to London, England, looking south. You can change this to your own home by using Preferences. You can set a new location using:
  • The Location panel
  • The Observer sub-panel
  • The Choose location dialog (Control menu; for Earth's surface only)
    You can move your location by fixed steps in any direction relative to an object in the Solar System using the Control panel (Control position mode)

    21.1 The Location panel

    Using the Location panel, you can:

  • Use the Location type menu to set a new location mode
  • Open the Observer sub-panel
  • Use the Select location body: pop-up menu to choose a different Solar System body to be located on or to set your location in space (Heliocentric)
  • Use the Select surface feature: pop-up menu to choose a named location when on a Solar System object which has named surface features. The named surface features are cities and observatories on the Earth and landing sites and features on Venus, Mars and the Moon.
  • Enter new longitude and latitude co-ordinates
  • Change your distance (from the current location body)

    21.2 Location modes
    Location mode defines your type of motion through the space. Use the drop down menu in the Location panel to choose one of four location modes:
    Observe from surface mode - use for observing from a fixed location on (or above) the surface of a body (the normal mode for a terrestrial observer)

    • Space: track surface mode - use for observing a planet or moon's surface. As time changes the observer travels through space with the selected body whilst tracking a fixed location on the surface of the body
    Space: track body mode - use for observing a planetary system, or an body such as a comet or spacecraft. As time changes the observer travels through space with the selected body whilst tracking the center of the body. The observer's position is fixed in relation to the body's orbit (in the case of a planet or moon, the body will rotate beneath the observer)
    Space: heliocentric - used for observing the Solar System
    TIP: to get a better understanding of these modes, choose Motion preview from the Control menu; an illustration of your present location mode and aim will be shown.

    TIP: If you are interested in viewing the surface maps of objects (such as planets and moons) in greater detail, choose track surface mode. Open the Location panel fully (click the re-size button in the top right of the panel) and then choose Map from the height pop-up menu.

    TIP: It is useful to display the Ecliptic plane (Filters, guides, ecliptic) when viewing the solar system in Heliocentric mode. This provides a frame of reference to help you visualize your position.

     More about Location modes
    When we are standing on the Earth's surface, our motion in relation to the Sun and the stars is quite complex. We are turning with the Earth's rotation, and also moving with the Earth around its orbit of the Sun. In the case of an Astronaut standing on the Moon, there is the Moon's orbit round the Earth to be added. On top of all that, the Sun is moving in relation to the stars, and RedShift takes account of that.
    In order to allow you to simulate interesting views RedShift can fix your position in relation to solar system bodies taking account of all these motions. Each location mode uses a particular co-ordinate system, or frame of reference.

    Observe from surface mode and Space: track surface use the planetographic co-ordinate system:

    Latitude is measured in degrees north and south of the planet's equator. The zero point is the intersection of the planet's equator and the zero meridian (uniquely defined for each object which has a surface)
    Height is measured from the body's surface.

    Space: track body mode uses the orbital co-ordinate system:

    Latitude is measured in degrees north and south of the orbital plane.
    Latitude in the orbital system is the angular distance, measured eastwards, along the orbital plane from the zero point. The zero point is the direction to the gravitational center (the
    Sun for planets, a planet for its satellites, etc.)
    Distance is measured from the body's center.

    Space: heliocentric uses the Heliocentric (ecliptic) co-ordinate system:

    Latitude is measured in degrees north and south of the ecliptic.
    Latitude in heliocentric system is the angular distance, measured eastwards, along the ecliptic from the zero point. The zero point is the northern Vernal equinox.
    Distance is measured from the Sun.

    21.3 Setting a new location
    RedShift 3 lets you set your location anywhere on Earth or any other planet, moon, comet, asteroid or spacecraft. You can also set a heliocentric location (i.e. anywhere in space near the Solar System).

    The Select location body box displays the name of the currently selected body, relative to which your position is calculated. Select a new body or select a heliocentric location using the Select location body: pop-up menu. If the body that you require isn't on the menu, then select Find from the pop-up menu, and choose to locate on it from its entry in the Find dialog. NB: you may need to make the body visible using the Filter dialog in order to see it.
    Note that selecting a Heliocentric from this menu also selects Space: heliocentric mode in the Location type menu. You must select an object using the Select location body menu before you can choose a Location type relating to the surface of an object.

    Select a new viewing location on the currently selected body by choosing one of the named sites from RedShift's extensive gazetteer. The Select surface feature pop-up menu contains a list of towns and cities and well known observatories on Earth. Gazetteers are also provided for the Moon, Mars and Venus (instead of towns, cities and observatories, the gazetteer lists geographic features and landing sites of space missions). To find more features, choose Find location from the surface feature pop-up.
    Where a named site (feature) has been selected, the name is displayed in the Surface feature box.
    You can also set a new location using the Observer sub-panel. The Observer sub-panel provides additional flexibility in setting your location (see section 21.6 below).

    21.4 Entering new location co-ordinates
    Click the re-size button in the top right of the Location panel to display/hide the co- ordinate and height/distance boxes.
    Edit the fields in the Location co-ordinates box to enter:
    Longitude and latitude on any body which has a surface
    Orbital co-ordinates relative to the selected body (indicated by an 'o' after lat and long)
    Heliocentric co-ordinates (position relative to the Sun).

    Remember that longitude and latitude co-ordinates correspond to the selected Location type:
    Planetographic - for Observe from surface or Space: track surface modes,
    Orbital - for Space: track surface/body modes (indicated by an 'o' after lat and long)
    Heliocentric - for Space: heliocentric mode.
    You can enter new co-ordinates by editing the fields in the longitude and latitude box. Click a value to select it then type new values. Use the tab key to step through each of the longitude and latitude values. Press Return/Enter to apply your new location settings.

    Longitude/latitude are set using three fields: degrees, minutes, and direction (W, E, N, S or +/-)...Type W or E to the right of the longitude field (or use the pop-up menu) to change between West and East longitudes. Type N or S to the right of the latitude field (or use the pop-up menu) to change between North and South latitudes.

    Use Relative... in the co-ordinates pop-up menu to choose pre-set directions from which to view an object.
    For Observe from surface and Space: track surface location modes choose one of the six pre-set positions in relation to the object. For example, for a planet:
    North pole: directly above the north pole of the object
    South pole: directly above the south pole of the object
    Equator/0: directly above the equator at the zero meridian
    Equator/180: directly above the equator at longitude = 180
    Equator/90W: directly above the equator at longitude = 90W
    Equator/90E: directly above the equator at longitude = 90E


    For Space: track body location mode choose one of the six pre-set positions in relation to the center of orbit (the Sun for a planet, the planet for one of its moons). For example, for a planet:
    Inward: between the Sun and the planet. (Orbital latitude and longitude = zero)
    Outward: with the planet between you and the Sun (always in shadow unless phases are switched
    off). (Orbital latitude = 0; longitude = 180)
    Leading: in front of the planet in its orbit (Orbital latitude = 0; longitude = 270)
    Trailing: behind the planet in its orbit (Orbital latitude = 0; longitude = 90)
    Above: looking down on the northern hemisphere. (Orbital latitude = +90)
    Below: looking up at the southern hemisphere. (Orbital latitude = -90)

    21.5 Setting height and distance
    Use height/distance to control your height above, or distance from an object. When your location is set on the surface of a planet or moon, height can be entered in kilometres above the surface. In Space: track surface/body modes the distance is measured in kilometres, or thousands/millions of kilometres. In heliocentric mode, distance is measured in astronomical units (a.u.) or in millions of kilometres from the Sun.
    Use the height/distance field to enter new values. Click the current value to select it then type new values. Use the height/distance pop-up menu to select distance units. Press Return/Enter to apply your new height/location settings.
    Use distance = zero to observe from the center of the selected object.

     21.6 Using the Observer sub-panel
    The simplest way to change your location relative to a selected object is to use the Observer sub-panel. Click Observer button in the Location panel to open the Observer sub-panel.
    Rotate the mini-globe by dragging it. Change your location by dragging the yellow stick marker. The co-ordinates of the new location (displayed in the upper right corner) are expressed using the current co-ordinate system (for example in Space: track body mode planetographic co-ordinates are displayed).
    Change the distance from the center of an object or height above its surface using the slider at the bottom of sub-panel. Drag slider to change distance from the planet. Arrows allow fine adjustment of distance.
    Use the Shadow and Grid buttons to show/hide a shadow (phase) and grid on the mini-globe in Observer sub-panel. Note that displaying a shadow and grid on the mini-globe does not affect the display settings for the object in the sky window. The globe will respond faster with shadows and grid off.
    Click the Find button in the Observer sub-panel to search for a named site in the gazetteer for the currently selected object. The Find dialog lets you choose from a list of towns and cities or a list of well known observatories. Gazetteers are also provided for the Moon, Mars and Venus (instead of towns, cities and observatories, the gazetteers list geographic features and landing sites of space missions).

    21.7 Changing position using the Control panel

    You can move through a sequence of locations using the Control panel (Position mode). Choose Position mode from the pop-up menu in the Control panel (or press F5 on the keyboard). If necessary, open the panel fully by clicking the resize button in the top right of the panel. Use the horizontal and vertical controllers to move your position left or right and up or down. Click the play arrows to move continuously through either axis using the currently defined step size (expressed as degrees and minutes). Click the stop button to stop continuous movement. Click the buttons immediately to the right and left (and above/below) the stop button to move one step at a time, or use the corresponding arrow keys on the keyboard.
    Note that RedShift does not allow you to move over the pole of a planet or moon. Continuous above/below movement stops at the north or south poles of the object.

    Edit the value in the Step field
    to change the current step size,
    or use the pop-up menu to select
    one of the pre-set values.

    Alternatively, you can move through a sequence of distances from the location body. Choose Distance mode from the pop-up menu in the Control panel (or press F6 on the keyboard). Use the vertical controller to move your position towards or away from the location body. Click the play arrows to move continuously using the currently defined step size. Click the stop button to stop continuous movement. Click the buttons immediately to above/below the stop button to move one step at a time, or use the corresponding arrow keys on the keyboard.

    Edit the value in the Step field to change the current step size. Change units using the pop-up menu. Units can be set to meters, kilometres (thousands/millions) or astronomical units. You can also set units to be the radius of the currently selected object.