August 1996

by Steve Stefanik

Ordinarily August hosts the annual Perseid meteor shower as it has since 36 B.C.. But, this might be the year skywatchers have long been waiting for! Although the last several years have been pretty good with regard to fair weather and clear nights this year’s rendition will peak two days from a "new" moon, on the night of the 11/12th, allowing observers to view the event with little or no interference from the waning crescent moon.

To observe the Perseids, face northeast and look for the constellation Perseus, a winding group of stars below and to the right of the familiar "W" which is the constellation Cassiopeia. This is the radiant or the point from which the meteors appear to radiate, although the meteors can streak across the sky in any direction.

What makes the Perseids worth watching is the possibility of seeing 100 or so extremely bright and fast (60 kilometers per second) meteors per hour some of which leave trails of smoke.

The origin of the shower is a trail of cosmic debris left in the wake of comet Swift-Tuttle in its 130 year orbital cycle. These tiny sand-sized meteoroids careen headlong into the earth’s atmosphere and burn up due to friction with the air. What makes the Perseids so fast is the fact that they are traveling around the sun in the opposite direction that the earth does so their velocity is added to that of the earth’s.

Although some Perseid meteors streak across the sky before midnight, a greater number occur in the early morning hours when the earth’s rotation turns us head-long into the stream of particles left behind by comet Swift-Tuttle.

Speaking of comets, this month Hale-Bopp becomes a naked-eye 6th magnitude object in the constellation Ophiuchus above and to the right of the familiar "teapot asterism in the constellation Sagittarius. It passes between two globular clusters, NGC 6517 and 6539 on the night of the 6th. Through binoculars you may be able to see debris coming off its nucleus in the form of a fan-shaped tail illustrating the process by which meteor showers such as the Perseids originate.

As the sun gives way to darkness under August skies, look for the elusive planet Mercury low on the western horizon not far from the brightest star Regulus in the constellation Leo. Because Mercury is the closest planet to the sun, it rarely strays very far from it but on the evening of the 21st it reaches its greastest eastern elongation (27 degrees east of the sun).

Jupiter joins the array in the early evening low in the southeastern sky. It dominates the stars of the southern milky way in the constellation Sagittarius shining at magnitude -2.6. On the night of the 24th a waxing gibbous moon four days from full passes just north of Jupiter.

The following night, the moon passes just north of the planet Neptune in eastern Sagittarius which is difficult to locate this month because it has dimmed to 8th magnitude from last months naked-eye opposition.Uranus is still a naked-eye object in nearby Capricorn.

After Jupiter passes our local meridian around 10:00 p.m. check the eastern horizon for fellow first magnitude gas giant Saturn amidst the stars of Pisces.

As Saturn passes the meridian in the wee hours of the morning look for the brilliant beacon which is the planet Venus along with dimmer Mars low in the east among the twin stars of Gemini. On the morning of the 10th a crescent moon joins the pair. Venus reaches its highest point on the 19/20th when it rises more than 3 1/2 hours before the sun.