Perseid meteor shower, Jupiter’s Io, Guardians of the Pole

The Perseid Meteor Shower, the best known of the many meteor displays that return annually, will take place under optimum conditions this year because there’s no moonlight to interfere. Peak viewing nights are Wednesday, August 11, and Thursday, August 12. There are indications the peak may even extend into the next night, so consider August 12–13 as well. At peak, the zenithal hourly rate of the Perseids can reach 100 per hour, but this is an idealized number with the radiant at the zenith and stars visible to magnitude 6.5. Moreover, that rate might last only an hour. Most observers under good skies will see closer to 50 per hour. The Perseid meteors, like other similar annual meteor showers, occur when the Earth plows through a broad stream of tiny dust particles left over from the past disintegration of a comet. The particles burn up as air friction slows them at heights of about 50 miles, resulting in luminous trails visible for a second or two from the ground. Following the passage of a particularly bright meteor, a lingering glow, called a train, sometimes remains for a few seconds or more. This year’s display takes place during the dark of the moon, ensuring a dark sky as long as you observe from a location far from city lights. Lie in a comfortable position, facing northeast, under an open sky, for best results. Strong coffee is advised.

The curve of the crescent Moon Thursday evening points toward Venus, some two fists at arm’s length to the moon’s lower right. Look for fainter Spica about half as far to the moon’s left. In good seeing, a telescope should show the tiny black shadow of Jupiter’s moon Io leaving Jupiter’s western edge at 10:14 pm EDT (start looking earlier!), closely followed by Io itself budding off from Jupiter’s edge 10 minutes later. The Big Dipper hangs diagonally in the northwest after dark. From its midpoint, look to the right to find Polaris (not very bright) glimmering due north as always.

Polaris is the end of the Little Dipper’s handle. The only other Little Dipper stars that are even moderately bright are the two forming the outer end of its bowl: 2nd-magnitude Kochab and 3rd-magnitude Pherkad. On August evenings, you’ll find them to Polaris’s upper left (by about a fist and a half). They’re called the Guardians of the Pole, since they ceaselessly circle around Polaris through the night and through the year.

The above comes from the Outdoors listings in the Reader compiled by Jerry Schad, author of Afoot & Afield in San Diego County. Schad died in 2011. Planet information from SkyandTelescope.org.