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Wednesday, 12 August 2009

The Perseid Meteor Shower

Active July 23-August 20

Radiant RA 03h 04m Dec +58°
The undoubted stand-out for meteor observers in the summer of 2007 is a very favourable return of the Perseids, peaking on Aug 13d 02h UT in dark, moonless skies. At this time, just as dawn is approaching for observers in the British Isles, the Perseid radiant will be high in the eastern sky and from locations away from artificial light pollution rates of around a meteor per minute should be attained. In most years, the Perseids produce corrected ZHR around 80 at maximum, with rates at half that level on Aug 11-12 and 13-14. Indeed, watches on any night in the 10-day interval centred on Perseid maximum are likely to be very productive for the patient observer: this is a great time for new observers to try their hand at meteor work! All else being equal, best rates are found when the Perseid radiant – near the 'Sword Handle' on the Perseus-Cassiopeia border – is highest in the sky during the pre-dawn hours. Even in early evening, however, the radiant is already quite favourably placed:

Local Time (53 oN) Radiant Altitude Local Time Radiant Altitude

21h 28.1° 01h 52.8°

22h 32.8° 02h 59.3°

23h 38.4° 03h 67.1°

00h 44.7°

Observers should bear in mind the nightly eastwards 'drift' of the Perseid radiant e to Earth's orbital motion. In early August, the radiant is 15 degrees west of its position at maximum (given above), to the north of Andromeda.

New Moon falls on August 12, and the Perseid maximum night of Aug 12-13 (a Sunday to Monday) will be free from lunar interference. Productive watches become possible from about Aug 6-7 onwards, with the waning crescent Moon retreating into the morning sky and rising later from night to night.

Perseid meteors are produced by debris from Comet 109P/Swift-Tuttle. Incoming meteoroids have atmospheric entry velocities of 60 km/s, resulting in very fast meteors. A healthy proportion of Perseids are bright, making the shower a good target for photography. Perseids brighter than about magnitude 0 can be captured at film speeds of ISO 400 or greater with a camera fitted with either a 50 mm standard lens or 28 mm wideangle lens at f/2.8 or faster, using time exposures aimed towards Cygnus or the Square of Pegasus. These need not be driven – 'static' cameras yield images with meteors appearing as longer streaks cutting across the short arcs of star trails. Users of conventional film can try exposures of 10-15 minutes' duration. Some observers enjoyed success with digital exposures of 30 seconds' duration in 2005: obviously, these demand availability of sufficient memory as a night's operation may amount to as many as 500 images!

Being fast meteors, Perseids – particularly the brighter examples – often leave behind persistent ionisation trains.

As one of the year's most consistent very active showers (alongside the Quadrantids and Geminids), the Perseids justifiably enjoy favour with even casual observers. The 2005 return was well-observed from the UK, showing a typical strong peak with ZHR 70-80 and the usual abundance of bright events. It appears that the enhanced Perseid activity attending the 1992 perihelion return of the parent comet is now behind us, but the shower's regular, fairly dependable performance makes this a continued highlight of the meteor observer's year. Circumstances of the shower could hardly be more favourable for the UK in 2007, both in terms of the absence of moonlight, and the timing of maximum: observers should make the most of this opportunity – moonlight will severely restrict viewing in 2008.

Observations of these, and other less-active showers, together with sporadic activity, will be welcomed by the Meteor Section. Observing instructions can be found on the website at:

Send reports and enquiries to the Meteor Section Director:

Neil Bone, 'The Harepath', Mile End Lane, Apuldram, Chichester, West Sussex, PO20 7DZ

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The Perseids are Coming


July 31, 2009: Earth is entering a stream of dusty debris from Comet Swift-Tuttle, the source of the annual Perseid meteor shower. Although the shower won't peak until August 11th and 12th, the show is already getting underway.

Brian Emfinger of Ozark, Arkansas, photographed this early Perseid just after midnight on Sunday, July 26th:

"I used an off-the-shelf digital camera to capture this fireball and its smoky trail," says Emfinger. "It was a bright one!"

Don't get too excited, cautions Bill Cooke of NASA's Meteoroid Environment Office. "We're just in the outskirts of the debris stream now. If you go out at night and stare at the sky, you'll probably only see a few Perseids per hour."

"Earth passes through the densest part of the debris stream sometime on August 12th. Then, you could see dozens of meteors per hour."

For sky watchers in North America, the watch begins after nightfall on August 11th and continues until sunrise on the 12th. Veteran observers suggest the following strategy: Unfold a blanket on a flat patch of ground. (Note: The middle of your street is not a good choice.) Lie down and look up. Perseids can appear in any part of the sky, their tails all pointing back to the shower's radiant in the constellation Perseus. Get away from city lights if you can.

There is one light you cannot escape on August 12th. The 55% gibbous Moon will glare down from the constellation Aries just next door to the shower's radiant in Perseus. The Moon is beautiful, but don't stare at it. Bright moonlight ruins night vision and it will wipe out any faint Perseids in that part of the sky.

Above: Looking northeast around midnight on August 11th-12th. The red dot is the Perseid radiant. Although Perseid meteors can appear in any part of the sky, all of their tails will point back to the radiant. Image copyright:, used with permission.

The Moon is least troublesome during the early evening hours of August 11th. Around 9 to 11 p.m. local time (your local time), both Perseus and the Moon will be hanging low in the north. This low profile reduces lunar glare while positioning the shower's radiant for a nice display of Earthgrazers.

"Earthgrazers are meteors that approach from the horizon and skim the atmosphere overhead like a stone skipping across the surface of a pond," explains Cooke. "They are long, slow and colorful—among the most beautiful of meteors." He notes that an hour of watching may net only a few of these at most, but seeing even one can make the whole night worthwhile.

The Perseids are coming. Enjoy the show.

Perseid Meteor Shower Peaks August 12th, 2009

by Kevin Brown : last updated: June 18, 2009

Every year in early August, we can observe the Perseid meteor shower ("the Perseids"). And it's a fascinating sky event.

Here's a beginners' guide to what it is and how best to enjoy it. (Perhaps, impress your friends with these astronomy questions and answers!)

What are the Perseids and what is a meteor?

Every year in August, the Earth passes through rock and dust fragments left behind by the comet Swift-Tuttle, last time it came near the Sun. As these small particles collide with the Earth's atmosphere, they burn-up, often creating a startling streak of light across the sky.

You can easily observe this and it can be a wondrous spectacle.

Why is it called the Perseid meteor shower?

The term "Perseid", refers to the star constellation of Perseus.

View of Perseid meteor radiant point, above NE horizon after midnight

The meteors actually have nothing to do with the stars we see from Earth, as being part of Perseus. It just appears as though the meteors originate from Perseus.

In fact, the rock fragments are close to the Earth – that's why they burn in our atmosphere.

They are very close, just a few hundred miles – not many, many light years distant like the stars.

But, if you trace-back the bright trails of meteors we see, they appear to originate from the stars of Perseus.

When can you see them?

The Perseid meteor shower actually starts in late July and runs to late August. However, the best time to view is around the peak.

It's not precise, but the 2009 peak is expected on August 12th at around 15.00 hours UT. There is some uncertainty, so it's very worthwhile to observe either side of this.

In particular for European observers, the hours of darkness either side the peak hours, may well prove more fruitful! So try the previous Tuesday night, as well as the night of Wednesday 12th.

And there is also a potentially prominent Moon to contend with. It will not set below the horizon until the early hours of the morning.

What equipment do you need to observe the meteor shower?

The good news is none! Just use your eyes.

It will help your observation if you give your eyes some time (say 15 minutes), to become adapted to the darkness.

Binoculars my also help, but on the other hand, they may restrict your view to a small part of the sky.

The meteors originate in the region of Perseus, but they may appear in view just about anywhere in the sky. Although, if you were to track-back their trails, you would get to Perseus.

Can they be measured, at all?

Yes. Keen astronomers count how many appear in a fixed period of time, in a certain area of the sky. This is expressed as a Zenithal Hourly Rate (ZHR).

We may expect around 100 streaks of meteor light across the sky per hour, at or near the shower peak.

Do watch out for them on Wednesday 12th August and during hours of darkness, before and after.

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