This applet will generate a view of the sky for an observer anywhere near, or inside, a black hole. By dragging the blue circle below the image, you can reposition the viewpoint relative to the hole; clicking on the distance slider takes the viewpoint straight to the point you click. You can also move by hitting the left or right arrow keys, with the shift key down for larger steps.
By dragging the line of sight pointing out from the circle, you can change the direction the observer is facing. The up and down arrow keys rotate the line of sight by 15°, or 90° if the shift key is down. The two lines to either side mark the boundaries of the field of view; to shift to a wider or narrower view, use the first pop-up menu on the left.
The default view is 127° wide, and this alone introduces some distortion at the edge of the image (this is especially apparent if the black hole is near the edge). Also, the provisos concerning blueshifts and brightness mentioned on the main tour page apply.
You can generate the view for observers in various kinds of motion. (Use the second pop-up menu.) This superimposes additional Doppler shift and aberration effects on the gravitational blue shift and distortion. The choices are:
The third pop-up menu lets you change the limits on the distance scale.
The fourth pop-up menu lets you choose the number of visible stars (in the entire sky, not in any specific view).