Full disk Hα images acquired on August 22 (17:42 UT, top left), 25 (16:40 UT, top right), 28 (16:43 UT, bottom left) and 31 (16:37 UT, bottom right) by the Mauna Loa Solar Observatory. This sequence shows that in the days before its eruption the filament is “U-shaped”, with a westward and an eastward branch. Only the eastward and narrower part of the filament (the one visible close to the limb in the August 31 image) will be ejected starting from  ~19 UT.