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.
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