The Perseid meteor shower comes around once a year, and it is one of the best. This year we will get an extra stellar look with a moonless sky. Starting the night of August 12 watchers can expect to see about 100 shooting stars per hour during this meteor shower! You won’t need any extra equipment to see it either, as their fiery streaks will be visible with the naked eye.
What causes the Perseid meteor shower?
The Perseid meteor shower is due to the comet Swift-Tuttle. It’s name comes from the fact it radiates from the Perseid constellation. So if you can’t find it from all the shooting starts, search out the constellation first. Swift-Tuttle orbits the sun once every 133 years, completing one orbit for every 11 orbits of Jupiter. Swift-Tuttle makes close approaches to Earth every year and will swing perilously close in 2126 with current estimations. If it hit Earth, it would have 27 times the energy of the Cretaceous-Paleogene impactor. That is the impactor that took out the dinosaurs. For that reason, comet Swift-Tuttle has been described as “the single most dangerous object known to humanity“.
What causes a meteor shower?
Meteor showers are caused by comet debris evolving into Earth’s orbit. Imagine the comet as a dirty snowball left over from winter. As the comet streaks through space it can break up into small pebbles. It also can have a water vapor tail as the ice warms and sublimates near the sun. That vapor can drag the dust and little particles with it. As those tiny space rocks fall towards Earth they get extremely hot in Earth’s atmosphere. As they light on fire and fall through the night sky they look like shooting stars!
If the comet takes 133 years to orbit, why do we see the Perseid meteor shower every year?
Dr. Skocpol brought up an important point. Comet Swift-Tuttle orbits our sun every 133 years. How could we possibly see the meteor shower every year? How could it happen like clockwork? Always in early August? When Comet Swift-Tuttle has its closest approach to the sun it melts down and breaks apart leaving a trail of comet dust. That trail of comet dust is what Earth orbits through every year. As we go through the comet dust our atmosphere interacts with some of it, creating meteor showers. The gif below shows Earth and Comet Swift-Tuttle orbiting around our sun. Because the comet is in a different plane than Earth we only see one Perseid meteor shower per year from the comet instead of two!
1 thought on “Perseid meteor shower: Best of the Year”
The comet goes around the sun only once every 133 years [on the same undisturbed orbital path]. Yet we see the meteor shower every year! To some in your audience, that may seem like a crazy contradiction. However, you could explain that the comet has been leaving “cookie crumbs” all along its orbit each time it goes around the Sun, and we (Earth) keep crossing that trail (the comet’s orbital path) every year. The comet doesn’t have to be there each year, and indeed we hope that it isn’t, if we want to avoid that big, bad collision.
But that got me to thinking about another question. The meteors in the shower all are coming from the same part of the sky (marked by the far-away Perseid stars) when the Earth gets to its Aug 12-13 position. One possibility is that the comet and/or its “cookies” move slowly compared to the Earth at this crossing point. In that case the Earth is plowing through the slowly moving “cookies”, and the Earth is headed toward Persied at that time. Another possibility is that the comet and its “cookies” have a much larger orbital speed at the crossing than the Earth does. Then the Earth becomes a target for “cookies” coming from the direction of Persied. That is how we tend to talk about it, but is it what really happens? After all most people talk about the Sun rising and setting as it goes around the Earth, but really the Earth is rotating once a day.
Rosie’s Research Helpers can help solve this by either of two different approaches. One is to find out and compare the speeds of a “133-year comet” and a “1-year planet” at the same distance from the sun. The other is to find out about the direction of the comet’s orbit (pointing back to the distant stars) when it crosses the Earth’s orbit.
By the way, I myself don’t know the answer to this (yet).
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