Astronomy news for the week starting Friday, May 19, 2000.
This is a bit of an odd week, as the Moon spends its time in a
transition phase, a week in which it does not go through one of its
four quarters. Beginning with the Moon just past full, the entire
week is filled with the waning gibbous, third quarter not reached
until Friday the 26th. In between, on Sunday the 21st, the Moon
passes its apogee, when it is farthest from Earth.
Friday the 19th sees a conjunction low in the west-northwest
between Mercury and Mars in Taurus that is seen only in twilight
and that will not be possible to observe without binoculars. The
other ancient planets hide close to the Sun as well, Jupiter,
Saturn, and Venus now on the other side, to the west of it.
Technically morning objects, they are quite impossible to see. The
only planets available for "easy" viewing are Uranus and Neptune
(forgetting ultra-faint Pluto), and of these, only Uranus, slowly
moving against the stars of eastern Capricornus, is visible to the
naked eye, and then just barely. These two planets are still more
or less in line. Neptune began retrograde two weeks ago, and now
it is Uranus's turn, as the seventh planet reverses its direction
and goes to the west beginning Thursday, the 25th.
That great symbol of the northern skies, the Big Dipper -- the
"plough" in Britain and the central figure of Ursa Major, the
Greater Bear -- is now at its best for early evening viewing. In
mid-northern climes it is nearly overhead at 9 PM. Far off the
disk of the Milky Way, Ursa Major is filled with galaxies, some
near, some far. Four, Messiers 51 and 101 (near the end of the
handle) and Messiers 81 and 82 (northwest of the Bowl) are easily
visible in small telescopes, or even binoculars. Not far off the
bowl, the Hubble Space Telescope imaged 3000 distant galaxies in an
angular span only 1/10 the angular diameter of the full Moon,
suggesting that as many as a trillion galaxies are accessible to
view over the whole sky. Closer to home, the middle five stars of
the Dipper, all about 80 light years away -- are an actual cluster
joined together by gravity. Moving through space together, they
were all born at the same time within a long-since dissipated
interstellar cloud of the sort that make the naked-eye structure of
the Milky Way. The Sun was probably once part of a similar cluster
that long ago dissipated, its siblings now lost. Bisect the
Dipper's handle to the south, and your vision will pass through a
more traditional cluster, Coma Berenices (Berenice's Hair), which
looks like a handful of diamonds flung against a jeweler's velvet.