Tiny particles of comet dust will be “smashing through Earth’s atmosphere” all weekend…here’s an expert opinion on what it is and how to see it.
Each year in August the skies throughout the northern hemisphere light up with the residual streaks of a comet gone by—AKA the Perseid Meteor shower. It is one of the most well-known and prolific meteor showers for us Earthlings to witness, which during optimal viewing years can render the sky brightly illuminated with dozens upon dozens of streaking lights per hour.
Anxious for a bit of expert insight into this celestial occurrence, we reached out to Bing Quock, Assistant Director of Morrison Planetarium at the Academy of Sciences in San Francisco, to ask some mete-oriented questions about this week’s Perseid (pronounced per-see-id) lightshow and what to know about watching it. Take a read….and find someplace dark this weekend to get a good look.
To start, can you explain the basics of a meteor shower? What exactly is happening up in space when we watch a phenomenon such as Perseid?
What we’re seeing with the Perseid meteor shower (as with all other meteor showers) is the earth is passing through the trail of dust that was left behind by a comet at some time in the past. And since comet paths are looping through the inner solar system, Earth passes through them at the same time every year.
When a meteor shower occurs, you can see more meteors than you would on an ordinary night, [when] normally, you might see between 2–4 meteors per hour early in the evening, and maybe double that just before dawn. During a meteor shower—depending on which shower—you might see several dozen meteors per hour. For the Perseid meteor shower the typical average is usually given as 60–80 meteors per hour. Now, that is under ideal conditions, which means a moonless night, clear sky, away from city lights. This year is not ideal, because the moon will be almost full, so it’s light is going to wash the fainter meteors from view.
With that in mind, my understanding is that there is a range of days when this particular meteor shower can be seen?
Sure, because the moon is approaching full on the day of the peak [estimated to be August 12 to the 13th] it might be a good idea for people to watch a few nights before the peak, so say…starting on Friday or Saturday night. But usually it’s good to spend a couple of night’s watching, don’t just concentrate on one single night.
Do we know specifically which comet this meteor shower is derived from? And does the debris that causes these showers vary from different comets?
Yes, it is from a comet called Swift-Tuttle; named after its two main co-discoverers.
The materials may vary a little bit. These are tiny particles — it could be silicate material, or rock or tiny bits of metal. Because they are liberated by comets they are most commonly bits of rock that are the size of a grain of sand or a grain of rice. And they’re actually not falling through the atmosphere, but Earth is moving into them. Earth moves through its orbit at about 66,000 mph, so when it runs into a stream of dust particles that are just sitting out there, these particles find themselves smashing through the atmosphere at 66,000 mph. And depending on the direction the comet’s path is coming from, the speed of the meteor particles might even vary from that.
There are some meteors that are catching up to Earth and so they don’t move that fast through the atmosphere. Others are slamming into Earth’s orbit head-on, so they might be moving faster. The Perseid meteors, in particular, are typically said to be moving twice as fast, so the figure that is often given is around 60 kilometers per second..and that’s fast enough to heat up the particles as they slam through the atmosphere. And they can get up to a couple thousand degrees, which causes that streak of light that you see in the sky.
And just to clarify something you said: the light we see in the sky is from a meteor that can be as small as a grain of sand?
Yes, it’s caused by a particle about the size of a grain of sand. Now, the light can be bright because it is something that is burning at a couple thousand degrees. And the amazing thing about this is that when you see a meteor in the sky it is typically burning up about 50 miles above the ground; so this tiny particle of space dust is burning up 50 miles above the ground and still causing that streak of light which you can see.
Are there certain factors which can result in a more robust shower on any given year?
Sure. If the parent comet of the shower has just swung by and resupplied the dust in that trail, then you might see a more intense shower than usual. One shower that is very famous for that is the Leonid meteor shower which takes place in November. Every thirty-three years or so its parent comet comes by and re-supplies the dust. So in the past there have been some Leonid meteor showers which have resulted in several hundred or even a thousand meteors per hour. So it can be quite spectacular, but we’re not expecting that from the Perseids this year.
The average person watches a meteor shower and seems excited just to see the light show. Is there something in particular that an astronomer watches for and would be of special interest to them?
Astonomers are always interested in trying to get a count of how many meteors are seen, because that gives them an idea of how dense the dust stream is that the Earth is passing through.
And it’s my understanding that when it comes to meteor showers, the best way to view is simply the naked eye?
Yes, you want as wide of a view as possible, so binoculars or a telescope would only restrict your view.
So you want to get up on a hill where you have a low horizon around you. Look up and be patient. It’s the most important thing for meteor shower watchers to do—be patient. You need to give yourself at least 20 minutes away from bright lights to let your eyes adapt to the darkness, that way you’re more likely to see the fainter meteors. Don’t try to Tweet or Facebook your observations because the screen of your phone is going to ruin your night vision.
Any well-known spots in the Bay Area for viewing meteors?
Mount Tam is usually said to be pretty good, although they close it at 7 p.m. unless you’re camping there. The East Bay Hills are another pretty good location. But the main thing is to get away from the bright city lights.
If these are annual occurrences, which other showers should we watch for?
There are a number of good meteor showers every year. The Perseids is generally considered one of the better ones. Another good one takes place in December. It is called the Geminid Shower, and that one is said to be a little bit better than the Perseids. Not too many people know about that one because it takes place during the winter, when people don’t want to be out at night looking at meteors. But during the summer for the Perseids, it’s warmer at night, more comfortable staying out late, so not as many people are aware of the Geminids as they are of the Perseids. But those are generally the two best meteor showers of the year.
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