Going backwards.
"She was supposed to be astern while she was sleeping."
The stern is the back end. Astern is 'toward' the stern.
motion
Comparing one motion to another.
a quick motion
set into motion
The 'a' is Old English for 'onward' - so ahead is onwards forward and astern is onwards backwards.
Windage losses are reduced by fitting the astern turbine in the lowest area available exhaust end of the astern casing. also by fitting hood over the last stage of astern and ahead blades also by fitting astern turbine in its own casing
Capillary motion is a movement of liquids in small tubes. This motion can be also ascensional.
it is an expected
That is the definition of motion
It is motion in a straight line at a constant velocity.