Best spot to aim for. Aiming farther left gives you a better angle towards the star.
Aim under the V-shaped top of the grey wall texture with the middle of the top crosshair approximately horizontal to where the lowest part of the sky can be seen through the wall. Other reference spots are available however, take a look at the above image and try to find some spot on the wall that you can remember to aim at.
This will also work
This will work too
Here is a visualization of all of the possible cannon shots that will work. The green area means that it will work with minimal dust, the yellow area means that you will need a lot of dust, and the red area will not work at all.
