WWW.ASTRONOMY.COM 25
get the expansion rate. Thirty
years of Hubble observations
have pinpointed the expan-
sion rate at 73 kilometers per
second per megaparsec (one
megaparsec equals 3.26 mil-
lion light-years). Oddly
enough, measurements from
the European Space Agency’s
Planck satellite give a value of
67, and scientists have yet to
Hubble has studied the
aftermath of Supernova 1987A
throughout its 30 years in orbit.
In this view, released in 2011, the
progenitor star’s tattered remains
appear as an irregular blob at
center, while the bright ring
surrounding it consists of material
the star released 20,000 years
earlier that the supernova’s shock
wave is lighting up. NASA/ESA/PETE CHALLIS
(HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS)