August Sky Notes
Meteors - The Perseids
August means shooting stars on the astronomical calendar, with the annual Perseid meteor shower reaching a peak. The Perseids are one of the more reliable meteor showers, and given the time of year undoubtedly the most widely observed by the general public. Conditions this year however will not be ideal, with the moon just a few days off full, drowning out many of the fainter meteors.
Sometimes known as 'The tears of St. Lawrence', the martyred Christian deacon whose feast day falls on Aug 10th, just two days before the Perseids peak, these particular ‘tears’, like the majority of meteor showers, are composed of debris deposited over many thousands of years by periodic comets. Perseids are associated with comet Swift Tuttle which takes around 130 years to orbit the Sun. Perseid meteoroids are not dissimilar in size and density to that of instant coffee granules with the occasional pea or marble sized fragment. Each August, Earth encounters various strands of the Swift-Tuttle debris stream giving rise to the eagerly anticipated shooting stars.
Perseid meteoroids penetrate the upper atmosphere 60 miles above us at speeds of 43 miles/second, interacting with atoms as they do so, before becoming ionised and releasing a packet of light. It is this brief luminous flash we call a meteor. Particularly bright examples often leave behind persistent ionisation trails in their wake, the classic shooting star. The radiant of the shower, the location in the sky from which the meteors appear to emanate, lies within the constellation of Perseus, which in August is rising in the north east during the evening. Perseid activity is highest from Aug 8th-15th reaching a peak this year over the night of Aug 12/13th.
Under ideal conditions the zenith hourly rate (ZHR) for the Perseids is typically 80-100, but moonlight will effect matters, restricting numbers to under 15 per hour, perhaps rising to 30 plus in the hour before dawn on the 13th. If observing view in areas of the sky a good hand span away from Perseus and around between 40-70 degrees above the horizon. Good luck.
The Late Summer Sky
With resumption of astronomical twilight, the majority of stars in the summer sky are visible by 10pm. The familiar saucepan outline of the ‘Plough’ (part of Ursa Major, the Great Bear) hangs high in the NW, the arc of its handle pointing down in the direction of brilliant Arcturus in Bootes the Herdsman, located in the W. Note the delicate starry circlet of Corona Borealis situated to the upper left of Arcturus. Use the ‘pointer’ stars in the ‘bowl’ of the Plough to locate the pole star-Polaris in Ursa Minor. Do not mistake the conspicuous circumpolar star Capella, visible above the N horizon during late summer, as the North Star. Much of the SW aspect of the sky is occupied by just two large, but rather faint constellations. The figure of Hercules is best identified by the ‘keystone’ asterism that resides upper left of Corona. Below Hercules stands the vast, ill-defined outline of Ophuichus, the serpent bearer, which extends down towards the SW. Just above the horizon in this direction look for bright orange hued Antares in Scorpius. Sagittarius follows Scorpius across the S horizon, although both groups never fully rise over the UK. The large asterism known as the ‘teapot’ sits on the horizon and is the most distinctive part of the Archer. The bright planet Jupiter sits just ahead of this asterism, with Saturn following on after the teapot’.
The lower regions of the SE and E are occupied by yet more zodiac constellations, including Capricornus - the Sea Goat (SSE), Aquarius - the Water Bearer (ESE) and Pisces - the Fish (E). None are particularly easy to trace from light polluted skies.
Almost equal in brightness with Arcturus, steely blue Vega in the small lozenge shaped pattern of Lyra rides high overhead. Along with Deneb and Altair, it makes up the ‘summer triangle’. Deneb sits at the tail of Cygnus high to the ENE, whilst pearly Altair in Aquila the eagle resides midway up in the South. Look for the two small but distinctive patterns of Sagitta and Delphinius straddling an imaginary line drawn between Deneb and Altair. Climbing off the NE horizon is the great hero Perseus. The familiar 'W' pattern of Queen Cassiopeia holds court above. Her daughter, the princess Andromeda is located lower right and is marked by a chain of stars extending towards the winged horse Pegasus which occupies the mid regions of the E sky. This group is best identified by 'the square of Pegasus' - four reasonably prominent stars enclosing an area seemingly devoid of stars. The sight of these stars in the sky signifies the impending arrival of autumn.
Mark Dawson,
Whitby & District Astronomical Society
For more information about Whitby & District Astronomical Society see: www.whitby-astronomers.com
August means shooting stars on the astronomical calendar, with the annual Perseid meteor shower reaching a peak. The Perseids are one of the more reliable meteor showers, and given the time of year undoubtedly the most widely observed by the general public. Conditions this year however will not be ideal, with the moon just a few days off full, drowning out many of the fainter meteors.
Sometimes known as 'The tears of St. Lawrence', the martyred Christian deacon whose feast day falls on Aug 10th, just two days before the Perseids peak, these particular ‘tears’, like the majority of meteor showers, are composed of debris deposited over many thousands of years by periodic comets. Perseids are associated with comet Swift Tuttle which takes around 130 years to orbit the Sun. Perseid meteoroids are not dissimilar in size and density to that of instant coffee granules with the occasional pea or marble sized fragment. Each August, Earth encounters various strands of the Swift-Tuttle debris stream giving rise to the eagerly anticipated shooting stars.
Perseid meteoroids penetrate the upper atmosphere 60 miles above us at speeds of 43 miles/second, interacting with atoms as they do so, before becoming ionised and releasing a packet of light. It is this brief luminous flash we call a meteor. Particularly bright examples often leave behind persistent ionisation trails in their wake, the classic shooting star. The radiant of the shower, the location in the sky from which the meteors appear to emanate, lies within the constellation of Perseus, which in August is rising in the north east during the evening. Perseid activity is highest from Aug 8th-15th reaching a peak this year over the night of Aug 12/13th.
Under ideal conditions the zenith hourly rate (ZHR) for the Perseids is typically 80-100, but moonlight will effect matters, restricting numbers to under 15 per hour, perhaps rising to 30 plus in the hour before dawn on the 13th. If observing view in areas of the sky a good hand span away from Perseus and around between 40-70 degrees above the horizon. Good luck.
The Late Summer Sky
With resumption of astronomical twilight, the majority of stars in the summer sky are visible by 10pm. The familiar saucepan outline of the ‘Plough’ (part of Ursa Major, the Great Bear) hangs high in the NW, the arc of its handle pointing down in the direction of brilliant Arcturus in Bootes the Herdsman, located in the W. Note the delicate starry circlet of Corona Borealis situated to the upper left of Arcturus. Use the ‘pointer’ stars in the ‘bowl’ of the Plough to locate the pole star-Polaris in Ursa Minor. Do not mistake the conspicuous circumpolar star Capella, visible above the N horizon during late summer, as the North Star. Much of the SW aspect of the sky is occupied by just two large, but rather faint constellations. The figure of Hercules is best identified by the ‘keystone’ asterism that resides upper left of Corona. Below Hercules stands the vast, ill-defined outline of Ophuichus, the serpent bearer, which extends down towards the SW. Just above the horizon in this direction look for bright orange hued Antares in Scorpius. Sagittarius follows Scorpius across the S horizon, although both groups never fully rise over the UK. The large asterism known as the ‘teapot’ sits on the horizon and is the most distinctive part of the Archer. The bright planet Jupiter sits just ahead of this asterism, with Saturn following on after the teapot’.
The lower regions of the SE and E are occupied by yet more zodiac constellations, including Capricornus - the Sea Goat (SSE), Aquarius - the Water Bearer (ESE) and Pisces - the Fish (E). None are particularly easy to trace from light polluted skies.
Almost equal in brightness with Arcturus, steely blue Vega in the small lozenge shaped pattern of Lyra rides high overhead. Along with Deneb and Altair, it makes up the ‘summer triangle’. Deneb sits at the tail of Cygnus high to the ENE, whilst pearly Altair in Aquila the eagle resides midway up in the South. Look for the two small but distinctive patterns of Sagitta and Delphinius straddling an imaginary line drawn between Deneb and Altair. Climbing off the NE horizon is the great hero Perseus. The familiar 'W' pattern of Queen Cassiopeia holds court above. Her daughter, the princess Andromeda is located lower right and is marked by a chain of stars extending towards the winged horse Pegasus which occupies the mid regions of the E sky. This group is best identified by 'the square of Pegasus' - four reasonably prominent stars enclosing an area seemingly devoid of stars. The sight of these stars in the sky signifies the impending arrival of autumn.
Mark Dawson,
Whitby & District Astronomical Society
For more information about Whitby & District Astronomical Society see: www.whitby-astronomers.com
