Tales of the Occultation
Rao, Joe, Natural History
This month, during the morning hours of the 19th, skywatchers can see a waning gibbous Moon pass in front of the firstmagnitude star Aldebaran. This event-called an occultation (from the Latin for "hiding")-is the seventeenth in a series that started in August 1996 and will end on February 14, 2000.
During the late evening hours of the 18th, note how quickly the Moon (three days past full) approaches the orange star: about a full Moon's width per hour. To witness the actual occultation you'll need binoculars, as the Moon's glare will overwhelm Aldebaran for naked-eye viewers. Aldebaran disappears behind the bright (forward) edge of the Moon and, about an hour later, emerges from behind the unlighted (and unseen) part of our satellite. As though a switch were turned on, the star reappears.
The exact moment of the star's disappearance and reappearance differs by location. For those in the far west, the occultation will take place between approximately 1:00 and 2:00 A.M., PDT; for the mountain time zone, from 2:25 to 3:25 A.M.; for the central time zone, 3:50 to 4:50 A.M.; and for the eastern time zone, 5:15 to 6:25 A.M.
Interestingly, Saturn is also in the midst of a series of monthly occultations, the first of which occurred in April 1996. Until last month, these occultations were either invisible from the United States or took place during the daylight hours. The current series continues this month with the Moon occulting Saturn on October 15, but only those who live in Africa and Asia will be able to see it. The next two Saturn "eclipses" occur on November 11 and December 9 and can be seen in many parts of the United States. The Saturn series will end on March 29, 1998, with an occultation visible from parts of Antarctica.
The Sky in October
Mercury is not visible as it passes through superior conjunction, moving beyond the Sun as seen from Earth, on October 13.
Venus is in the southwest throughout the month and sets more than one and a half hours after sunset. …