Preparing for the Perseids
The summer’s premier (and one of the year’s best) meteor shower – the Perseids – will peak during the evening/predawn hours of Aug. 12-13. This is when the Earth, in its orbit around the sun, intercepts the Perseid meteor stream.
Unfortunately, as is sometimes the case, the moon interferes, as will the waxing, gibbous moon this time around. All is not lost though, as this shower is known for its bright fireballs; the possibility of seeing several streak across the night sky, even as the moonlight washes out the majority of fainter meteors, is quite good.
The Perseid meteor shower’s radiant (apparent point of origin in the night sky) lies in the constellation of Perseus - the Warrior Prince, which during mid-August clears the NE horizon around 10 p.m., and is directly overhead around 4 a.m.
The Perseids are debris associated with Comet Swift-Tuttle, a comet discovered in 1862 by astronomers Lewis Swift and Horace Tuttle. It has an orbital period of approximately 133 years.
The Perseid shower is usually a reliable and prolific meteor shower, with a zenith rate (under a moonless sky and from a dark site) of about 100-plus meteors per hour. Lasting from around July 17 to Aug. 24, it will still be possible on any clear night to catch sight of some of the later Perseids after they peak.
To see the greatest number, start watching the night sky as soon as it turns dark. You may see some meteors skim across the Earth’s upper atmosphere. If possible, try to put a tall object like a tree or building between you and the moon.
The best, and most comfortable, way to observe any meteor shower is to lie on a blanket on the ground or a lounge chair, with a pillow behind your head and an extra blanket to keep the late night/early morning chill and mosquitos at bay. If you place the NE horizon behind you, you will stand the best chance of maximizing the number of meteors seen, as the meteors will be radiating out across the sky from that direction.
Of course, the later you stay up, the higher the Perseus constellation will rise in the night sky, until the radiant is directly above you around 4 a.m., and the meteors will then radiate downwards, streaking towards all points of the horizon.
While waiting for the Perseids, there is still much to see in the night sky. In addition to the many bright stars and constellations, two bright planets are visible. Even the waxing moon will not wash out glorious Jupiter shining high in the southwest sky as the early evening sky darkens.
Binoculars will show the four largest Galilean moons – Io, Europa, Callisto and Ganymede – circling Jupiter. To find Jupiter, look for the brightest point of light just under and slightly to the right of the waxing, gibbous moon on the night of Aug. 9. Jupiter remains visible almost the entire night, not setting in the southwest until the pre-dawn hours. The bright, reddish star to the lower right of Jupiter is Antares (“Rival of Mars”), the heart-star of Scorpius - the Scorpion.
Though Saturn shines only at mag. +0.2 (10 x fainter than Jupiter’s mag. -2.4), it is still readily visible to the far left of Jupiter in the southern sky as it darkens.
On the evening of Aug. 11, Saturn (still in the “teapot” asterism of Sagittarius - the Archer) sits immediately to the left of the near-full, gibbous moon. Like its larger sibling, Saturn stays up until the pre-dawn hours.
Having made its inferior conjunction with the Sun last month, Mercury has transitioned from the evening sky to the morning sky. It should be visible above the east-northeast horizon about an hour before sunrise during the middle two weeks of August, though it will be too close to the sun to be readily visible during the month’s final week.
On Aug. 9, Mercury reaches its greatest western elongation (angular distance from the Sun as seen from Earth), and highest point in the pre-sunrise sky.
Until next time, clear skies. Glenn K. Roberts lives in Stratford, P.E.I., and has been an avid amateur astronomer since he was a small child. His column appears in The Guardian every two weeks. He welcomes comments from readers at glennkroberts@gmail.com.