Summer 1999

The Summer Sky
by Dr. Whitney Shane, MIRA’s Charles Hitchcock Adams Fellow

Fixed Stars
As the Milky Way reappears in the summer sky, you will see little evidence that the Galaxy has a spiral form. Although long suspected, it was not until about 1955, when the first maps of the hydrogen gas distribution were made, that we first clearly saw the galactic spirals.

With the lack of dramatic new ideas, interest in this problem has been declining, but the cause of these motions remains a perplexing question.

Planets
Mercury will be visible in the morning sky from the northern hemisphere during most of August.

Venus will be very bright in the middle of July, but it will then drop quickly in the west as it nears inferior conjunction. In September it will reappear in the morning sky, reaching maximum brightness toward the end of the month.

After passing opposition in April, Mars will recede into the south-west evening sky during the summer and will become increasingly difficult and unrewarding.

Jupiter will become more easily visible in the morning sky as the summer progresses. It will commence its retrograde motion on August 25.

Saturn becomes more easily observable during the summer, as it follows Jupiter across the sky at a distance of about 1 hour. Note, for example, that the almost full harvest Moon will be 4 degrees south of Jupiter in the early morning of September 27 and 3 degrees south of Saturn on the following morning, demonstrating, once again, that the Moon moves about 15 degrees per day. It will commence retrograde motion on August 30.

Uranus and Neptune will both pass opposition during the summer, Neptune on July 26 and Uranus on August 7. Both will be occulted by the Moon each month, but only the occultation of Neptune on July 28 will be visible from our region.

Meteor Showers
The always-reliable Perseids will be visible for a few days around August 12 under unusually favorable conditions, with practically no moonlight to interfere. The much less numerous delta-Aquarids might be seen in the morning hours during the week around July 29, but this will coincide with full moon, so little is to be expected.

Eclipses
We certainly hope that everyone who can manage the trip will observe the last solar eclipse of the millenium on August 11. It will pass from the western Atlantic over south England, Europe, the middle east and India. The maximum will be in eastern Europe, but the best viewing conditions are expected in Turkey, where there should be many MIRA representatives. For the stay-at-homes there will be a partial lunar eclipse, which will commence around dawn on July 28.