Adjusting orientation of the sky map

You can tweak various settings to make the orientation of the sky map match the view through your optical instrument.

First, pick the coordinate system that matches your mount. For an equatorially mounted instrument, switch to the Equatorial Coordinate mode in the View menu. The option to toggle the coordinate system should read Switch to Horizontal View (Horizontal Coordinates) when the current mode is Equatorial Coordinates. For an altazimuth-mounted instrument or naked-eye viewing, switch to Horizontal Coordinates, so that the option in the View menu reads Switch to Star Globe View (Equatorial Coordinates). This sets the base coordinate system used to render the sky map, and also sets the reference for the orientation of the skymap: zenith or north.

If your instrument is using an erecting prism, typically used on Schmidt-Cassegrain and refracting type telescopes, the view through the eyepiece will be mirrored horizontally. You can have the sky map match this by checking the Mirrored View option under the View menu.

Next, to rotate the sky map freely, you can hold down the Shift key and drag the mouse on the sky map. A temporary overlay will appear showing the direction of north and zenith at the point, and displaying the angle they make with the vertical in a counterclockwise sense. The orientations of zenith and north will update as you rotate the sky map. Letting go of Shift or the mouse button will stop the rotation operation. As you pan the sky map or focus it on different objects, the rotation you set is retained as an offset from the reference direction. The reference direction is north when using Equatorial Coordinates and zenith when using Horizontal Coordinates. As a reminder, the reference direction is solid and brighter in the temporary overlay. For the two common orientations of erect and inverted, the rotation can be set / reset using the ViewSkymap Orientation submenu. Select "North Down" or "Zenith Down" as is applicable to set an orientation of 180 degrees.

If you are visually observing through an eyepiece of an instrument, you may need to do some more correction. For the common case of a large Dobsonian telescope (or more generally a Newtonian design mounted on an altazimuth mount), a systematic additional correction is of help. This correction applies because we stand erect while using the telescope irrespective of the angle the telescope tube is making with the ground. So as we move the telescope in altitude, an additional correction depending on the altitude of the object needs to be applied to make the sky map match the view through the eyepiece. This correction is enabled by checking the Erect observer correction checkbox in the ViewSkymap Orientation submenu. This correction only makes sense in Horizontal Coordinate mode and is disabled when using equatorial coordinates.

Finally we provide some examples of how to use these settings for various instruments:

  • Naked-eye observing: Choose Horizontal Coordinates and a Zenith Up orientation under ViewSkymap Orientation.

  • Camera on an equatorially mounted telescope: Choose Equatorial Coordinates and adjust the orientation of the sky map so that it matches your camera. As your mount points to different regions of the sky, the orientation should be rendered correctly.

  • Using binoculars: Same settings as Naked-eye observing

  • Eyepiece of an altazimuth Schmidt-Cassegrain telescope with an erecting prism: Under the View menu, choose Mirrored View, and under the Skymap Orientation sub-menu, choose Zenith Up. Finally, tweak the rotation manually to match the eyepiece view according to the angle you are using for your erecting prism.

  • Using a RACI finder scope on an altazimuth mounted telescope: Same settings as Naked-eye observing, except you may need to tweak the orientation manually once if you have it mounted at an angle

  • Using a straight-through (inverted view) finder scope on an altazimuth mounted telescope: Choose Horizontal Coordinates and a sky-map orientation of Zenith Down in ViewSkymap Orientation submenu

  • Eyepiece of a Dobsonian telescope: Choose Horizontal Coordinates, and in the ViewSkymap Orientation submenu, select Zenith Down and check the Erect observer correction option. Then adjust the orientation manually once to match your telescope eyepiece view, and it should henceforth track it correctly.