Viewing the Late Summer and Autumn Sky

Wishing Upon a Star
Mark your astronomical calendar for August 11 and 12, for these days mark the annual peak of the Perseid meteor shower. For several nights on either side of these dates, the number of shooting stars, or meteors, that will streak across the sky will increase, rising to a crescendo on the morning of the 12th. Astronomers call this the Perseid meteor shower, since the origin, or radiant, of the shower is within the constellation Perseus.

For those of us in the northern hemisphere, Perseus rises in the northeast in the late evening. As a result, the shower is best seen between midnight and dawn's first light. On a good year, given dark skies, an observer may see as many as a meteor a minute on average, making the Perseids one of the year's finest showers.

Unfortunately, the light from the nearly Full Moon will obliterate all but the brightest Perseids this year, making 2000 less than optimal. At the peak, we might expect to see only about 20 meteors per hour.

Regardless of moonshine, use a reclining chair and dress warmly. Even though this is August, it can still get quite cool at night. Although the shower's radiant is in the northeast, meteors can appear to flash from any point in the sky, so look toward the darkest region, with the Moon to your back, and enjoy the show.

The Perseids may be traditionally the best annual meteor shower, but it is not the only such event. The Delta Aquarids are set to peak on the morning of July 29, with as many as 20 meteors an hour radiating from the constellation Aquarius. Fortunately, moonlight will not be a factor. Look toward the southeast between midnight and dawn.

Another meteor shower, the Orionids, peaks on October 22, with the radiant, in Orion, rising in the east after midnight. Typically, the Orionids produce about 15 to 20 meteors an hour, but again, moonlight will hamper this year's event.

Aurora
Most people think of the Sun as unchanging, but in reality, it varies ever so slightly over an 11-year cycle. As luck would have it, this year marks the peak of the solar-activity cycle. As a result, the Sun is experiencing an increased number of magnetic storms on its surface, which manifest themselves as sunspots, solar flares, and so-called "mass ejections." During these eruptions, streams of charged particles flow outward from the sun. If they make it here to Earth, they spiral along the force lines of our planet's magnetic field. As the particles interact with atoms and molecules in our upper atmosphere, they produce the beautiful aurora—the Northern Lights in the northern hemisphere and the Southern Lights in the southern hemisphere.

There are five types of aurorae, including auroral patches, rays, arcs, bands, and veils or curtains. All look like shimmering, iridescent clouds in the sky, with some displaying pastel colors of red, blue, and green, while others appear whitish. Displays are seen most frequently near Earth's magnetic poles, but some have been seen as far south as Miami, Florida and Honolulu, Hawaii.

There is no way of predicting exactly when the next aurora will occur, but the odds increase whenever solar activity is high. Spaceweather.com (www.spaceweather.com) issues regular updates on current solar activity, and even offers a free e-mail notification service for those who want to be on the auroral front lines.

Seeing your first aurora is an exciting event, especially if it is an intense display. If it is especially vivid, the aurora may bathe the entire sky in a wavelike, oscillating glow of faint colors. The memory of such an event will last you a lifetime.