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| ペルセウス座流星群が極大 |
月明かりに負けない明るい流星に期待
普段より目立って多くの流星を見ることができるのは、11日の夜から13日の夜までの3夜程度でしょう。いずれの夜も、21時頃から流星が出現し始め、夜半を過ぎて薄明に近づくにつれて流星の数が多くなると予想されます。
最も多く流星が見られるのは、13日の夜明けの頃（東京では3時台、以下同じ）と考えられ、空の暗い場所での流星数は1時間あたり30個程度が期待されます。前後の日ではこれより少なくなり、この前日にあたる12日3時台では1時間あたり15個程度、この翌日にあたる14日の3時台では1時間あたり20個程度の流星がそれぞれ見えそうです。
Under a truly dark, moonless sky, we might spot 50 to 80 Perseids an hour during the shower’s peak. But this year, the waning gibbous Moon will likely reduce that number by half, or more. The Moon rises around 9:30-10 pm, and it shines the entire night. While unfortunate, the Moon's presence isn't a deal-breaker.
Keep in mind that fainter meteors, the ones that moonlight will erase, typically outnumber brighter ones. Since the Perseids produce more fireballs — meteors as bright as, or brighter than, Venus — than any other major shower, their number will be unaffected. You could say that we’ll only see the cream of the crop this time around.
To further improve prospects of seeing more meteors, keep the Moon at your back so it doesn’t accidentally dazzle your eyes. As with all meteor showers, it’s not necessary to stare at the streaming point, called the radiant. Perseids flash in any and every corner of the sky. What unites them is that they all point back to their origin in northwestern Perseus below the W of Cassiopeia.
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