Perseid Meteor Shower/英仙座流星雨
August 12th, 2005
Pic from NASA
A colorful Perseid streaks over Half Dome in Yosemite National Park. Photo credit: Dirk Obudzinski, August 12, 2004.
July 22, 2005: Got a calendar? Circle this date: Friday, August 12th. Next to the circle write "before sunrise" and "Meteors!" Attach all of the above to your refrigerator in plain view so you won’t miss the 2005 Perseid meteor shower.
The Perseids come every year, beginning in late July and stretching into August. Sky watchers outdoors at the right time can see colorful fireballs, occasional outbursts and, almost always, long hours of gracefully streaking meteors. Among the many nights of the shower, there is always one night that is best. This year: August 12th.
The source of the shower is Comet Swift-Tuttle. Although the comet is nowhere near Earth, the comet’s wide tail does intersect Earth’s orbit. We glide through it every year in July and August. Tiny bits of comet dust hit Earth’s atmosphere traveling 132,000 mph. At that speed, even a tiny smidgen of dust makes a vivid streak of light–a meteor–when it disintegrates. The shower is most intense when Earth is in the dustiest part of the tail.
Perseid meteors fly out of the constellation Perseus, hence their name. The best time to watch is during the hours before sunrise when Perseus is high in the sky: sky map. Between 2 a.m. and dawn on August 12th, if you get away from city lights, you could see hundreds of meteors. Scouts, this is a good time to go camping!
Really, it could hardly be better. The Perseids come on a warm summer night. (Note: This is a northern hemisphere shower.) Other familiar meteor showers like the Leonids of November require a parka to enjoy. All you need for Perseids are light pajamas.
And there’s a bonus: Mars.
In the constellation Aries, right beside Perseus, Mars is shining like a bright red star. Step outside before sunrise, look east, and you’ll find you have a hard time taking your eyes off Mars. There’s something bewitching about it, maybe the red color or perhaps the fact that it doesn’t twinkle like a true star. It’s steady. You stare at Mars and it stares right back.
Earth and Mars are converging for a close encounter on October 30th. Consider August 12th a preview. Mars already outshines every star in the night sky, and it’s getting brighter every night. If you like August, you’ll love October.
And you will like August. Picture this: It’s four in the morning. The sky is dark. The breeze is pleasant. Mars is beaming down from the east while meteors flit across the sky.
Maybe you should go circle the calendar again.
几乎从未在夏季星空中缺席过的英仙座流星雨再度如期而至，并将于后天（13日）凌晨1时至3时30分上演一场今夏最灿烂的流星盛会。
据北京天文馆专家寇文介绍，英仙座流星雨是最有名的流星雨之一。近年来，它不但数量多，而且非常稳定，几乎从未在夏季星空中缺席过，因此被称为全年三大周期性流星雨（英仙座流星雨、双子座流星雨、天琴座流星雨）之首。
今年英仙座流星雨的活跃期从7月17日到8月24日，长达一个月以上。而8月13日凌晨1时至3时30分，流星雨的流量达到极大，每小时最大天顶流量在100颗上下。所以，明天晚上至后天凌晨，是观测的黄金时段。除了流量大之外，它还是高速流星群，流星流速高达每秒59公里。而且，由于当流星流量极大时辐射点的位置较高，且没有月光影响，观测条件非常理想。
难得的是，今年的英仙座流星雨很适合在北京地区观测，天亮时基本在头顶上方，所以不一定非要盯着辐射点方向看，流星可能出现在天上的任何地方。
英仙座流星雨非常漂亮，流星的亮度有的相当高，一些亮星抛撒时会在天空中留下一道长长的光痕，这些光痕就好比是流星划过夜空时投下的身影。本来流星划过时应是一条直线，但因有些流星在天空中会滞留一小会儿，短的几秒钟，长的可达数分钟，原本的直线就会变换成各种形态，有的成为烟状，然后慢慢扩散，光度越来越暗，直到消失在夜。
