Magnetic white dwarfs possess strong magnetic fields which can vary in the wide range 100 T–105T. Atoms and molecules of their atmospheres which are exposed to such extreme fields severely change their electronic structure and properties. In order to understand the observed spectra of magnetic cosmic objects it is indispensable to perform detailed investigations on atoms in strong magnetic fields. As a recent example, we discuss the explanation of the absorption features of GD229 through the transitions of the Helium atom in a field of the order of 5⋅104 T. The complicated scenario of the ground state crossovers for multi-electron atoms in strong fields is outlined for the example of the carbon atom.