Astronomers
and amateur skywatchers excited as perigee moon and comet Swift-Tuttle appear
together for dazzling skies
theguardian.com,
Press Association, Sunday 10 August 2014
 |
| The perigee moon, or supermoon, rises over Mount Eden in Auckland, New Zealand, on Sunday morning. Photograph: Simon Runting/REX |
A dramatic
supermoon is set to accompany this year's Perseid meteor shower, one of the
most anticipated events on the skywatcher's calendar.
Given a
dark, clear sky in a normal year, it is common to see more than 100 of the
meteors an hour during the second week in August. But this year the Perseids
have a bright shining rival. On Sunday, two days before the meteor shower
reaches its peak, the moon will become full.
Coincidentally,
it will also have reached the point in its orbit that is closest to the Earth,
known as perigee. The supermoon will be up to 14% bigger and 30% brighter than
other full moons during the year.
On one level,
this is bad news, according to Dr Bill Cooke from Nasa's meteoroid environment
office. "Lunar glare wipes out the black, velvety backdrop required to see
faint meteors, and sharply reduces counts."
But all is
not lost. The debris stream left by comet Swift-Tuttle, which produces the
Perseids, is wide, so the shooting stars could make an appearance well before
the moon becomes full. Cooke added that the Perseids were also "rich in
fireballs as bright as Jupiter or Venus" that would remain visible despite
the moon's glare.
A study
conducted by his team since 2008 has shown the Perseids to be the undisputed
"fireball champion" of meteor showers. "We see more fireballs
from Swift-Tuttle than any other parent comet."
Tony
Markham, director of the Society for Popular Astronomy's meteor section, also
urged skywatchers to stay optimistic.
"The
Perseids are rich in bright meteors and so many Perseids will still be seen
despite the moonlit sky background," he wrote on the SPA's website.
"You can minimise the effect of the moonlight by observing with your back
to the moon - possibly viewing the Cassiopeia/Cepheus/Ursa Minor area. If
possible, keep the moon hidden behind trees or a nearby building."
He pointed
out that at this time of year the moon is relatively close to the horizon,
leaving much of the sky dark. Markham also suggested looking at an area of sky
20 to 30 degrees away from the Perseid radiant – the spot near the
constellation of Perseus that the meteors appear to fly out from.
Every 133
years, comet Swift-Tuttle swings through the inner solar system leaving behind
a trail of dust. When the Earth passes through, the dust cloud particles hit
the atmosphere at 140,000 mph and burn up in streaking flashes of light,
creating the spectacle known as the Perseids.
The best
time to see the meteors is between Saturday and Wednesday, with activity
peaking on Tuesday. An unusually bright full supermoon was also seen on 12
July, and another is due to appear on 9 September. But the supermoon of Sunday
promises to be the most dramatic since this is when the moon will be at its
closest point to the Earth all year.
At perigee,
the moon is around 31,000 miles closer than when it is furthest away from the
Earth. Supermoons occur relatively often, every 13 months and 18 days, but are
not always noticed because of clouds or poor weather.
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