Perseid Meteor Shower Peaks Thursday Night

A meteor streaking across the sky.
Photo credit: Nick Ares, Wikimedia Commons.

Meteors, sometimes called "shooting stars", are more common than most people realize. So long as skies are clear and dark, even on ordinary nights there are an average of 2 meteors per hour.

Meteors start out as tiny bits of rock floating in space. Earth's gravity attracts these bits of rock, causing them to enter our atmosphere and fall toward the surface of our planet. Since they have such a long way to fall, they reach speeds of hundreds of thousands of miles per hour. At speeds like that, the air around them actually causes friction, and so each bit of rock and the air around it heats up. Voila, that's what you're seeing when you see a meteor! (Most of them are so tiny--about the size of a grain of sand--that they actually vaporize before they get anywhere near the ground. Nonetheless, they and the air around them glows so much that you can easily see it as it falls.)

Every few weeks or so, the Earth comes near lots of bits of rock that have floated away from the tails of various comets in the inner solar system. When that happens, we have many meteors fall to the Earth at one time--usually over the course of one or two days. This is what we call a "meteor shower". Every August, right around this time, we have one of the best annual meteor showers, when for one night, about 60 meteors can be seen per hour. (Perhaps the word 'shower' is a bit of an exaggerated name--if a droplet of water per minute come out of your faucet, you'd call that a 'trickle' and not a 'shower'--but that's just what we call these events.)

There are meteor showers about once every 4-6 weeks, but some are better than others depending on the year. The August meteor shower, known as the Perseid meteor shower, is one of the most predictable ones. That means that it may not be the most spectacular shower (others can have hundreds of meteors per hour), but it's a decent show, and it's consistent. Other showers deliver numbers much higher than that some years, but in other years are much, much lower. For these showers, the number of meteors per hour are very hard to predict.

This year the Perseid shower reaches its best on the night of Thursday, August 12, though you can still expect to see some meteors on the nights before and after the peak. Either way, all you need to do is find a place away from city lights (especially street lights), let your eyes adapt to the dark, and lay back on something comfortable with your head to the sky. If the shower delivers, you should see about 60 meteors per hour, or an average of one every minute.

Here are some news articles containing further information:

"Perseid meteor shower will light up night sky this week"

"OC sky's alive with meteors"

In Case You Missed the Eclipse...

Here in Orange County, a layer of coastal fog prevented anyone from seeing Saturday morning's partial lunar eclipse.

But lots of other people throughout the western United States, as well as eastern Asia, the Pacific Islands, and Australia, were treated to the event. One Orange County man, Dave Kodama, headed out to the Orange County Astronomers' private observing site located in the nearby desert, far away from city lights and rarely covered by clouds. There, he got an unobstructed view. He took this spectacular image, showing the Moon setting while still in the Earth's shadow. (If it looks far larger than it ever appears to your eyes, that's an effect of the telephoto lens he was using, which makes distant objects appear much larger than they actually are).

He also made the following video of the eclipse, from just before it began, to when the Moon starts to set (probably about 2 hours). Watch as Earth's shadow descends over the Full Moon:

One aspect of this eclipse that made it unique for observers in western North America was the fact that it occurred when the Moon was approaching the horizon. As anyone who has ever observed a rising or setting Moon knows, the Moon appears larger when near the horizon (a phenomenon known as the "Moon illusion"). It may surprise you to learn that the precise reason for this is still unsettled by scientists. The often cited notion that "you are able to compare it to objects of known size along the horizon", an instance of the optical illusion known as the "Ponzo effect", is considered inadequate by many scientists. But we can be sure it is definitely an optical illusion, and not some kind of magnification: witness the fact that the Moon appears the same size through a given telescope whether at the horizon or at the zenith.

Partial Lunar Eclipse!

You might be interested to know that there will be a partial lunar eclipse very early on Saturday morning (June 26), beginning at 3:17AM Pacific Time, and lasting until moonset, about 2 hours later.

What is a partial lunar eclipse?
A lunar eclipse occurs when the Moon passes into the Earth's shadow. During a lunar eclipse, as the Full Moon passes into the Earth's shadow, it begins to look like a part of it is missing--almost like a bite was taken out of it.

If the eclipse is total, the Moon gets completely covered by the Earth's shadow. Once it reaches the central part of the shadow (usually an hour and half into the eclipse), it will begin to glow red, for reasons having to do with sunlight bouncing off the Earth's atmosphere. But this eclipse is only partial, meaning that the Moon won't get completely covered by the shadow, so we won't see that this time around. Instead it will look like this:


What time should I look?
You're going to have to get up really early. The eclipse begins at 3:17 AM Pacific Time, and lasts until moonset, which for us tomorrow is around 5:12AM. 4:38 AM is the moment of greatest eclipse; at that point 54% of the Moon will be covered by Earth's shadow.




Is it worth getting up this early? What should I expect to see?
You should expect to see a portion of the Moon "missing". Since it's not a total lunar eclipse, you won't get to see the Moon enter the reddish glow of the Earth's inner shadow. Some people don't find partial lunar eclipses that interesting, because it does just look a little bit like a crescent moon, and you can see a crescent moon twice a month.

But if you enjoy astronomy, you will find this event interesting. Here are three reasons why:

1) This missing portion of the Moon isn't a lunar phase, like a crescent moon. We see a crescent moon twice each month because of the changing angle at which we're looking at the Moon as it goes around the Earth. During a lunar eclipse, the Moon's phase is at first full; we're seeing its entire face lit up by sunlight. So when a part of it suddenly goes missing in a matter of several minutes, you're actually getting to see the Earth's shadow! It's not just that you're looking at the Moon from a certain angle.

2) Lunar eclipses are a great opportunity to get to directly observe, with your own eyes, the fact that the Earth is a sphere (ball), not flat. How do we know? Simply notice the shape of the Earth's shadow as it is cast on the Moon: it's curved! In fact the ancient Greeks were the first to pay attention to this fact and realize that the Earth is a sphere.

3) For us here in western North America, Saturday's eclipse will occur when the Moon appears very large! This is because for us the eclipse will be occurring as the Moon is setting. You have probably noticed that when the Moon is rising or setting, it appears much larger than it does higher in the sky. (This is an optical illusion, by the way.)

Is it dangerous to look at?
No, not even slightly. Lunar eclipses are not dangerous. Solar eclipses--when the Moon passes in front of the Sun--require caution, but only because staring at the Sun is dangerous in general. (During the moments before and after a solar eclipse is the only time you are likely to accidentally stare directly at the Sun. This is why they make special "solar eclipse glasses," to protect your eyes.)

How often do lunar eclipses occur?
Lunar eclipses are much more common than solar eclipses. Lunar eclipses occur about once a year, though not everyone gets to see them, depending on the time the eclipse occurs. And as you can see with this eclipse, not every lunar eclipse is total. The last total lunar eclipse visible in North America was Feb. 21, 2008, and the next one will be this Dec. 21, 2010. You can find more information about when they will occur here.

What If the Earth Had Rings?

Very cool simulation! If the frame is cut off, you may want to click on the video and view it directly in YouTube.



(Hat tip: Michael D.)

Time-Lapse of Leonid Meteor Shower 2009

Video by Dave Kodama, Orange County Astronomers.

Given that this video was taken from very dark skies, it is evident what I meant earlier when I said that the term "shower" is a bit of a misnomer. Definitely note that the streaks which can be seen early in the video are from airplanes. Meteors are visible later in the evening after the constellation Leo begins to rise, about halfway through the video.

Go Watch the Meteors... Maybe

If you've heard the hype about this year's Leonid meteor shower (the Leonids are the annual shower that occurs in November), you might wonder why I've been reluctant to add my voice to the chorus imploring you to go watch it.

That's because meteor showers are total crapshoots. It's definitely not a terrible idea to set your alarm and spend at least a few minutes during the wee hours Tuesday morning, but with some caveats in mind:

First of all, if you haven't ever seen a meteor (or "shooting star"), there are almost zero qualifications to heed. You absolutely owe it to yourself to see one at some point, so consider going outside early Tuesday morning, provided it's clear, and keep your eyes on the sky for 10 minutes or so. You'll see at least one. Especially if you go somewhere fairly dark, i.e. somewhere where you can at least see some of the constellations.

But...

For all but a very few meteor events, I think the term "shower" is a bit of a drunk metaphor. On any given night, there are always meteors; the average is about 2 per hour, or so I've heard. This is because there are just that many random rocks (albeit very small: most meteors that we observe are only sand-grained sized, if you can believe it!) floating around the vicinity of Earth's orbit.

A so-called meteor 'shower' occurs when the Earth passes through an entire debris field of small bits of rock left by comets which have passed nearby in recent years. It may surprise you to learn that these events happen about once every month or so, and this is when the number per hour greatly increases: anywhere from 20 to 50 to 100, or, in this year's most optimistic estimate for November's shower, possibly as many as 300 per hour. Mind you that would mean seeing a shooting star about once every 12 seconds, rather than once every 30 minutes.

(I recommend the following articles for further information: Will the Leonids Roar Again? and The 2009 Leonids Are Coming!)

If that turns out being the case, it may be a really neat thing to watch. Definitely beats having to spend an entire hour outside to see one or two!

But something tells me that if when you go to bathe tomorrow morning, your water were to release a drop from the spigot once every 12 seconds, you wouldn't call that a "shower". So keep your expectations realistic!

This event, in 1833, in my judgment would have been more properly called a shower:

Nothing Amazing, Nothing Rare...

But it is neat: On Monday evening, October 26, 2009, Jupiter and the Moon will be a mere 3º apart (less than the size of your fist, at arm's length). Above: The view Monday night as predicted by Stellarium; click to enlarge.

Jupiter is currently the brightest object in our evening skies, but if you've not seen this planet with your own eyes, Monday evening presents you with perhaps the easiest opportunity ever to find it.

If you own a pair of binoculars or a small telescope, use them! The Moon looks spectacular with even the smallest optical aid, and often even small binoculars can allow you to detect Jupiter's four largest moons: the scene will appear as a bright "star" (Jupiter) surrounded by four tiny "stars" (Jupiter's four largest moons). The image below, taken by Mathew Wedel at 10 Minute Astronomy, gives you some idea:

On that note, it was exactly 400 years ago November that Galileo became the first human being to point a telescope at the sky and discovered the existence of those moons--and the existence of any object going around something other than the Earth! This represented the first direct evidence in support of the heliocentric theory of the solar system, and further fueled Galileo to uncover fundamental new truths about the nature of motion, laying the groundwork for the modern branch of science known as physics. Pretty pregnant observation, that.

Above: Galileo's own notes recording the relative positions of Jupiter's satellites over the course several days.