  Views of two bright prominence eruptions trackable all the way to 1AU are
here presented, using the heliospheric imagers on the Solar TErrestrial
RElations Observatory (STEREO) spacecraft. The two events first erupted from
the Sun on 2011 June 7 and 2012 August 31, respectively. Only these two
examples of clear prominence eruptions observable this far from the Sun could
be found in the STEREO image database, emphasizing the rarity of prominence
eruptions this persistently bright. For the 2011 June event, a time-dependent
3-D reconstruction of the prominence structure is made using point-by-point
triangulation. This is not possible for the August event due to a poor viewing
geometry. Unlike the coronal mass ejection (CME) that accompanies it, the 2011
June prominence exhibits little deceleration from the Sun to 1 AU, as a
consequence moving upwards within the CME. This demonstrates that prominences
are not necessarily tied to the CME's magnetic structure far from the Sun. A
mathematical framework is developed for describing the degree of
self-similarity for the prominence's expansion away from the Sun. This analysis
suggests only modest deviations from self-similar expansion, but close to the
Sun the prominence expands radially somewhat more rapidly than self-similarity
would predict.
