Perseid Meteor Shower

The Perseids are one of the most watched meteor showers. Occurring during northern hemisphere summer, the shower can be appreciated on a summer night. Quite a difference from the other reliable showers such as the Leonids and Quadrantids, that occur in November and January. Consider a warm summer evening under a dark sky full of stars, a picnic blanket, relaxing while shooting stars streak across the sky. What could be better?

The Perseid meteor shower occurs when the Earth passes through a stream of debris along the orbit of Comet Swift-Tuttle. This shower has been consistent throughout recorded history, mentioned in Chinese, Japanese and Korean records as early as the 1st century. Active from July 17th to August 24th, the shower will build slowly for weeks before the peak. A week before or after peak the shower can still be seen with around 20 meteors each hour. The shower is a northern hemisphere event, for southern observers the radiant never rises above the horizon.

A typical Perseid shower will produce up to 60-100 meteors an hour, what regular meteor observers would call 60-100ZHR. This is what a typical observer would see given a dark sky and good conditions with the shower radiant at zenith, a metric called zenithal hourly rate or ZHR. You can estimate this rate by counting the meteors seen in a shorter period. If you count the meteors that you see for ten minutes and multiply by 6 you would have a reasonable estimate of ZHR. As the rate of meteor arrival is irregular it is necessary to count for ten minutes or more to achieve a decent average rate. Conditions such as light pollution or clouds will result in some faint meteors being missed and a lower count.

Although the Moon is a waning crescent, three days after last quarter on August 12, it will rise from mid-northern locations around local midnight to one a.m. Its brightness and relative proximity to the Perseid radiant should be considered more of a nuisance than a deterrent, even so. Such mid-northern latitudes are the more favoured for Perseid observing, as from here, the shower’s radiant is usefully observable from 22h—23h local time onwards, gaining altitude throughout the night. The near-nodal part of the “traditional” maximum interval would be best-viewed from eastern Asia east to far western North America (with increasing moonlight for places further east in this zone), assuming it happens as expected. All forms of observing can be carried out on the shower, though unfortunately, it cannot be usefully observed from most of the southern hemisphere. – From the IMO 2012 Shower Calendar

Stargazing on Hawai’i

Here on the Big Island the single best place to stargaze is the Mauna Kea VIS. The dark skies are usually free of clouds and are well away from the lights of Hilo and Kona. After dark use for stargazing is not only permitted, but encouraged. It can be cold at 9,200ft, bring warm clothes and blankets

The timing for this years shower favors the West Coast of North America, across the Pacific to Asia. Thus Hawaii is well placed for viewing in 2012. The peak is predicted to occur from 07:00 to 19:30UT on August 12. This converts to 21:00HST on August 11th to 09:30HST on the morning of August 12th for Hawai’i. The radiant will rise about 10pm here in Hawai’i, starting the show. Moonrise will not occur until 02:30, only 16% illuminated it should not severely impact meteor observing.

Before 10pm, when the radiant is still low in the sky, keep an eye out for Earth-grazers, meteors that encounter the atmosphere at a low angle. Often these low angle meteors can streak across much of the sky, creating a spectacular event. The low angle allows the meteor to skim through the thin upper atmosphere without encountering thicker air and a quick demise. Do not expect a lot, but if you are lucky you may see one or two.

Watching meteors requires no more equipment than your eyes and a dark sky, and can be enjoyable for just about anyone. A good meteor shower is a great excuse to get out under a dark sky and enjoy the stars. Why not make a point to watch the Perseids this year?

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

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