People have fond memories sitting out on warm summer nights enjoying this annual meteor shower. It often gets some exposure by the media, but rarely do they take the time to explain some key aspects of the event. Let’s review some of these aspects to give everyone a better understanding of what to expect with the Perseids.
The media tends to focus on the “peak” date, But meteor showers can last for several days both before and after that peak date. With weather so fickle, take advantage of any clear sky both before and after the peak date. Although on any given clear night you can probably go out and see a couple of meteors streaking through the sky. These are sporatic meteors, not necessarily associated with a particular meteor shower. There is lots of “stuff” out there in space, and some of it makes it into our atmosphere every day.
A meteor shower is the result of Earth running head on into the debris trail of a comet that crossed on or near our orbital path around the Sun. As a comet devevelops its long tail, some of that dusty material is shed off and left behind. Think of it like a trail of breadcrumbs hanging in space. So every year when Earth gets to that spot in it’s orbit we hit that zone of debris. Over time, the dust starts to spread out and it takes a few days for Earth to clear that debris zone. Depending on the comet, sometimes their are multiple debris paths we can encounter. Scientists use modern radar to predict how many meteors we might see that particular year. The bottom line is that it is not an exact science and the hourly rates are just estimates. Occasionally, we can run into a small dense pocket of debris that will create the ultimate “meteor storm”. A rare but exciting event where the meteors may number in the thousands per hour rate. This year the peak dates for the Perseids are August 12th and 13th. But, if it is clear a few dates before and after the peak you should get out and try to see a few.
Now a reality check. As we have just explained, meteor shower rates are variable and they are assuming you are viewing under VERY dark skies. Astronomers’ definition of dark skies is way different than what most people think. For starters if the Moon is out when you are trying to look for meteors, that is not dark skies and you will see far less meteors than if the Moon is not in your sky. This year a three quarters full Moon will be rising around 10 PM. Astronomical dusk is not over until 9:46 PM, so that doesn’t leave much opportunity to be observing under dark skies. Plus the Moon will be in your sky all night long. Although the Moon will rise a little later each night, it still won’t be ideal for meteor observing.
Another big issue is your local sky. A lot of people think that just because the Sun goes down that it is dark out. Yes, there are some places where you may be far-far away from cities, towns and neighbors porch lights. For these few people, they may experience wonderfully dark skies full of twinkling stars. Reality check again – This is not here in Southeast Pennsylvania. This is really hard to explain to people who have never seen the beauty of truly dark night time skies. You will never experience those magical high hourly meteor rates you’ll hear about in the news. If you live out in Montana, on a Moonless night – go for it! The best skies we get here in Bucks and Montgomery counties in in the northern reaches. But even there it is no where near the darkness you might experience in the Poconos or the best spot in the Commonwealth – Cherry Springs State Park (Google it).
Another factor that effects hourly rates is that there is an ideal time to observe meteors, and unfortunately it is NOT in the early evening. It is actually a few hours before Sunrise. The explanation for this is a little lengthy and I won’t get into it here. Most people will look in the early evening rather than 3 AM. Again early evening observers will still likely see some meteors, but not those maximum rates you might be counting on.
Also bear in mind, these meteor streaks can occur almost anywhere in the sky. A meteor shower is named for the part of the sky where it “appears” the majority of the meteors come from. For the Perseids it is the constellation Perseus. The Leonids in November, the constellation is Leo, the Lion. Download a free August SkyMap from www.skymaps.com to locate Perseus. So you may want to focus most of your looking in that direction, the actual streak could appear almost anywhere in the sky. Your eyes can only look and focus in part of the sky, so once again you will miss some. If you are in a group and, each looking in different directions you may spot more than a single person looking in one direction.
So when you go out expecting to see a meteor every 40 seconds, that is probably not going to be what happens. When you also factor in the Moon, your location and timing, your numbers go way down. A few years ago we held an event at Lake Nockamixon, one of the better locations in the county (but far from ideal), on a Moonless night. During 4 hours of looking for Perseids, we saw 12.
Even though this reality check sounds bleak, that doesn’t mean don’t go out at all. Just have reasonable expectations that you’ll probably see a few of the brighter ones. Plus there is always that chance you may just get lucky and catch a bright slow moving fireball or that we duck into a particularly dense patch of the debris path and you will be treated to a virtual fireworks display of a meteors. But one thing is for certain, if you don’t go out at all, your meteor count will be zero. So go out with your SkyMap, sit or lie down and cruise the night sky for some Perseids. It’s also a great time to search out the constellation patterns in the sky, too.