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Find the average velocity with which Hydra I is running away from us
(why don't all the galaxies in Hydra I have the same velocity?) Use
the average velocity to find Hubble's constant. What value do you get?
Express
$H_0$
is
traditionally expressed in units of kilometres per second per Megaparsec.
The debate over the true value Measurements of Hubble's constant
is without have a
doubt
the longest long and
bitterest in the recent history of astronomy. For a
racy account of the ``Hubble Wars'' read `Lonely Hearts of the
Universe' by Dennis Overbye, controversial history,
and
several recent articles for a long time different groups using different methods to measure $H_0$
obtained widely discrepant results.
Fortunately, things have settled down in
New
Scientist recent years, and
Scientific American. One group of researchers, prominent
amongst whom is Alan Sandage of California, regularly find low values,
one of their latest being $H_0 = 42\ {\rm km}s^{-1}{\rm
Mpc}^{-1}$. Another group, including Jeremy Mould (until just recently
director of Mt Stromlo Observatory near Canberra) keep finding higher
values, around $H_0 = 80\ {\rm km}s^{-1}{\rm Mpc}^{-1}$. The the most recent
Hubble Space Telescope result was results from
ESA's Planck satellite give $H_0 =
68 67.8 \pm
6\ {\rm
km}s^{-1}{\rm Mpc}^{-1}$. Who do you agree with? 0.9$ km/s/Mpc, which is mostly
consistent with other measurements.
If your result is
not near any of these, different from this, take heart, Edwin Hubble's first measurement
was $H_0 > 400\ {\rm km}s^{-1}{\rm Mpc}^{-1}$!
\subsection{Age of the Universe}