Tag: meteor showers

Perseid meteors peak over the next few nights

By Phil Plait | August 11, 2012 10:47 am

The annual Perseid meteor shower peaks over the next night or two, so this is the best time to go out and look. I have a guide on how to observe the shower and a couple of links, too, but first indulge me a moment to talk about meteor showers.

The Earth orbits the Sun, as do comets. Comets are lumpy collections of gravel and dust held together in a matrix of frozen ice (usually water and/or carbon dioxide). As they get near the Sun, the ice turns into a gas, freeing the dust and gravel. This material follows in the same path of the comet like dirt flying off a dump truck on a highway. Over time – millennia – it spreads out into space.

The Earth plows into this stuff as it goes around the Sun. These tiny bits of cosmic jetsam burn up as they ram into our atmosphere at speeds of up to 100 kilometers per second, and we call them meteors.

Quick tip: a meteoroid is the solid bit of rock or whatever that travels through space. As it burns up in our air we call it a meteor. If it hits the ground, it’s called a meteorite. Now you can sound pretentious and correct people at cocktail parties!

The Earth is always being bombarded by meteors; about 100 tons per day burn up in the atmosphere. But that number goes up when we pass through the stream of matter that’s come off a comet – think of it as driving down a road and hitting the occasional insect. Then you pass near a creek and suddenly you slam into a swarm of bugs.

So yeah, meteor showers are the equivalent of that. But much prettier and less disgusting.

Every August the Earth passes through the debris from the comet Swift-Tuttle, forming the Perseids meteor shower.

[The best place to observe the shower is apparently in Sarasota, Florida. Yes, this is a real picture; I took it myself.]

They’re called the Perseids because they appear to come from the sky in the constellation of Perseus. It’s a bit like when you drive through a tunnel and all the lights on the sides appear to be moving away from a point ahead of you. It’s perspective, an illusion of sorts. In this case, the orbits of the Earth and the meteoroids add together to make the meteors appear to shoot away from the part of the sky where Perseus is. Other showers do this too, but from different parts of the sky, and the showers are named after their constellation. Thus, the Leonids, the Orionids, the Taurids, and so on. The Perseids are one of the best of the year, with about 50 – 60 meteors per hour visible (so on average one per minute at the peak). You may see fewer than that, but sometimes there are mini-peaks where the number goes up. It’s worth going out for an hour or two to see them!

So here’s a very quick rundown of what you need to observe the shower (Universe Today has a good, short guide as well):

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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Quadrantids meteor shower peaks – briefly – tonight

By Phil Plait | January 3, 2012 10:33 am

Tonight is one of the odder meteor showers of the years. Why is it odd? Well for one, it’s called the Quadrantids — named after a constellation that got redefined years ago and no longer exists. For another, the parent object of the shower isn’t a comet, it’s an asteroid that used to be a comet. And third, the shower peaks very sharply, coming and going in only an hour or two!

Here’s the deal.

First, meteor showers occur when the Earth plows through a trail of debris in space, usually left by a comet orbiting the Sun. The meteoroids — the solid bits of material — are usually very small, no bigger than a grain of sand. As they plow through our atmosphere at speeds of dozens of kilometers per second, they burn up, turning into meteors (if they hit the ground they’re called meteorites, which is very rare). Normally, you can see several random meteors every hour on a dark night, but during showers there may be dozens.

The length of time a shower lasts depends on how wide the debris field is. For most meteor showers it’s millions of kilometers wide, and so the showers can take days to play out. But the stream for the Quadrantids is very narrow, and the shower lasts for only an hour or so! It peaks tonight around 2 – 3 a.m. Eastern US time (07:00 – 07:00 GMT). That’s not an exact period, so if you want to see them you should go out an hour or so before then. There may be as many as 100 meteors per hour during that time!

Unfortunately, the waxing gibbous Moon is up tonight, so it’ll wash out a lot of the shooting stars. People on the east coast of the US have the best shot, since the Moon will hopefully have set by the time the shower peaks. However, Central time zone folks have a good view too since the Moon will be low to the horizon. I’ll give it a try tonight, since it peaks at midnight my time (in Boulder) and that’s early enough even for me to stay up.

How do you watch? All you need is an open sky and a place to lie down and relax. Someplace dark, away from trees and buildings is best. Meteors zip across the sky, so the more sky you see the better. I have a page with general advice on how to watch meteor showers that’ll help. It was written for a different shower, but the advice still applies.

As I said, meteor showers come from debris shed by comets as they orbit the Sun. These bits of stuff more or less follow the same orbit as their parent comet, and we get showers when the Earth rams through this material. However, the Quadrantids come from an object called 2003 EH1, which looks more like an asteroid — comets usually have lots of ice, but this object doesn’t. However, it’s on a comet-like orbit, so it most likely used to be a comet long ago which lost all its ice, leaving just rocky material behind.

And finally, the name: meteor showers appear to radiate from one point in the sky, in much the same way all the lights in a tunnel seem to be coming from ahead of you as you drive through that tunnel. Showers are named after the constellation where the meteors appear to come from: the Perseids for Perseus, the Orionids for Orion, and so on. Constellations are arbitrary boundaries in the sky, like state or county lines. Quadrans Muralis was a constellation defined back in the 19th century, and still existed when the Quadrantids were named, but was divided up when the modern official lines were drawn in 1930. That part of the sky is near the tail of the Big Dipper; so the meteors will appear to radiate away from the north across the sky.

So again, what to do: find a dark, open site. Try to bring a chaise longue or something where you can lie back and see lots of sky. Looking straight up is best. You don’t need binoculars or a telescope or anything like that: just your eyes, and a sense of wonder. Meteor showers can be a lot of fun, so I hope you see some good ones tonight!

Image credit: Randy Halverson. That’s not a meteor from the Quadrantids, but it’s still pretty.

Related posts:

12 things you need to see the Perseid meteors Sunday night (a general guide to meteor shower observing)
What a falling star looks like… from space!
New meteor shower points to a future close encounter
Will the Leonids roar in 2009?


Ten Things You Don't Know About Comets

By Phil Plait | April 20, 2010 6:00 am

I love me some comets.

I’ve seen quite a few in my time. Some were faint smudges in a big telescope’s eyepiece, some seen only in distant spacecraft images, and some so bright they were obvious and awesome to my naked eye.

They used to be considered harbingers, omens up for interpretation by mystics and people looking for reasons things happened the way they do. In reality, comets are just a class of objects in our solar system along with planets, asteroids, dust, and one biggish star.


Hmm. Did I say "just"? That’s unfair. They are gorgeous, interesting objects, worthy of study. And 100 years ago today — April 20, 1910 — we got a pretty good look at the most famous of them all, Comet Halley, as it passed the Earth at a distance of just 23 million km (14 million miles). It got so bright that it was obvious even when seen from cities. As geometry would have it, the Earth even passed through the comet’s tail, sparking fears of widespread death (cyanogen was detected in the comet, making people think it would poison them). It was the talk of the planet, featured in magazines and papers across the globe. For your history enjoyment, here is one of those articles from the 1910, transcribed by James Brooks. It gives a great flavor of the times.

To celebrate this remarkable centennial anniversary, I have put together Ten Things You Don’t Know About Comets. I imagine some readers will know some of these, and some will know all ten, but if you do you can still enjoy the pretty pictures — and make sure you click on them to embiggen ’em. And if you like this, I have several others, too (Ten Things You Don’t Know About… the Earth, Black Holes, Hubble, the Sun, Pluto, and the Milky Way), so check ’em all out and see how many things you don’t know.




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