Perseid over Idaho, 2012
The night sky is beautiful but generally isn’t dynamic. Other than the slow rolling of the entire sky as the night progresses (as if the stars were affixed to a sphere), there’s very little movement. Until you see the bright flash of a meteor. And a meteor shower can turn the sky into a show. The Perseid meteor shower may be easier to see than most. Its radiant is in the constellation Perseus, making it visible to most people in the northern hemisphere, where the majority of the Earth’s population resides anyways. It starts in mid July and peaks August 11th or 12th. August nights are longer than June or July nights, affording more time to view the shower, but are also warm enough to make lying or sitting still for long periods of time comfortable. The shower’s large footprint on the calendar makes it easy to coordinate viewing around a busy schedule.
And this year the Perseid viewing should be good. The peak nights happen to occur on a weekend when the Moon will be a waning crescent that only appears late – on the 12th it rises a few hours after midnight and won’t reach its highest point in the sky until well after the sun has risen. Unless you have to contend with forest fire smoke or clouds, it could be grand.
Is there a special technique to viewing a meteor shower? Here I will avoid insisting that you keep scientific records (time, apparent magnitude, constellation), and in fact will assume you are not particularly interested in photographing them (expensive SLR camera on a tripod). Make sure you have beverages and snacks. Warm clothing, blankets, or sleeping bags may not seem necessary on a summer night, but ideal viewing conditions are in areas with no clouds and low humidity, and thus radiational cooling and a cold night. Consider bringing a reclinable chair, cot, or air mattress. Seek the country – city lights are anathema to good viewing. Binoculars and telescopes are pointless unless there are other things you are planning on looking at. Don’t set overly-optimistic expectations: even at peak, one meteor a minute is the likely rate.
And now you’ll have to decide where to point your face. If a straight line is drawn through each meteor trail, all such lines will merge at a point called the radiant. Experts agree that looking directly at the radiant is not the best place to look. The closer a meteor starts to the radiant, the shorter its trail will appear to you, although paradoxically it means the meteor’s true path was pointed more directly at your head than others. But after discussing the radiant, opinions diverge. The advice at Spacedex is simply to “look approximately half way up the sky facing northeast…. Looking directly up at the sky or into the radiant is not recommended….” These people are wrong. Halfway up the sky in the northeast is where the radiant in Perseus will be, at least for the early night, so they’ve told you to look at the radiant and not to look at it in the same paragraph. Unfortunately the northeast is also the direction the moon will be rising in later, and you don’t want to ruin your night vision by looking at that.
Theoretically, to see the longest meteor trains, you should be looking 90 degrees away from the radiant. However, there are other factors to consider. Near to the horizon, the increased thickness of atmosphere leads to greater light scattering, decreasing the brightness of meteors there slightly but also increasing the amount of background light, thus leading to decreased contrast between meteor and sky and poorer viewing. Also , if you are looking towards the horizon, part of your field of view is of the ground, and meteors don’t appear there. Most of your field of view should be filled by sky. So just after sundown when Perseus is close to the horizon, you should be looking straight up. As Perseus rises in the northeast, you should consider looking slightly southwest and as the night progresses toward dawn look more to the west. If you get bored of the meteor show, consider looking at Perseus. Below him you will see the Moon and Jupiter, and later at night even Venus, all in the same area of sky.