Redshift 9 calculates the “Apparent Motion” of objects in two different ways.
If you use the standard horizontal coordinate system, the motion is calculated relative to the horizon. If, on the other hand, you switch e.g. to the equatorial coordinate system, the positions are calculated relative to the starry sky.
We have decided to offer both options, because with the horizontal coordinate system you can see where the object is located on the different days and can be observed in the sky. In this case, the rest of the sky (e.g. the stars) can of course only be displayed for the moment of the time currently set in Redshift 9. On the other days, they would appear in other places. The calculated position of the "Apparent Motion" diagram is therefore correct in relation to the horizon, but it is not correct in relation to the sky background (which can only be displayed for the time currently set).
If you instead want to see where the object (e.g. Mercury or Venus) is relative to the starry sky, for days in the past or future, you need to change the "Coordinate System" setting in Redshift 9 to, for example, "equatorial". Now the calculated position of the "Apparent Motion" graph is correct relative to the sky background, but not correct relative to the horizon. With this setting, the apparent retrograde motion of planets can be displayed in the best possible way in Redshift 9.
There is a message at the bottom of the screen indicating this difference. It appears every time the “Apparent Motion” feature is activated.