The Aladin stack shows all elements that have been loaded during your Aladin
desktop session. The stack is a pile of individual planes which can be pointed
images, HiPS surveys, catalogs, graphical overlays, filters, data cubes or anything.
Each time you load a new element, for example the HIPPARCOS catalog a new
plane would be added to the stack, usually at the top. To understand what is
displayed in the main Aladin panel, imagine you are looking through the
stack from the top: you see all elements, here the HIPPARCOS catalogue, SIMBAD data,
2MASS until you reach a opaque plane, usually an image plane in the
stack. Here the bottom plane is the DSS color image. Each plane can have three
properties, three elements: the first is a checkbox, the second is a trapezium icon
and the title. Clicking on the checkbox allows you to change the reference plane
so I can switch from 2MASS to ALL-WISE or DSS. Clicking on the trapezium
icon allows you to hide the corresponding plane, and clicking a
second time will show it again. And finally, clicking on the name of a plane
will make it the active plane: this means that buttons such as properties will
apply to this plane, so the properties here will open properties of the 2MASS
HiPS image. If you want to delete a plane from the stack,
make sure to first select it by clicking on its name, and then click the delete
button. Here you can select several planes by pressing the SHIFT key while
selecting them like this and in this case pressing the delete button
deletes all of them at once. That's all for the introduction to the Aladin stack,
we will show you more advanced usage in the next video.