The Perseid Meteor Shower and Other Stuff

by Stephanie Osborn
http://www.stephanie-osborn.com

FYI, there's a lot of hullaballoo about the Perseid meteor shower this year. Here's a little tidbit to explain why.

http://www.sciencealert.com/guys-the-perseid-meteor-shower-is-here-and-it-s-going-to-be-twice-as-good-this-year

Meteor showers are actually the debris left behind by comets. The tails blown off by the Sun form tiny particles in the swath of the parent comet's orbit, and when the Earth passes through it, the debris we run into flashes through the atmosphere and burns up, producing meteors. Most of these bits are the size of dust and sand; occasionally one is pebble-sized, which will be very bright.

This is why meteor showers are so predictable: we encounter the same orbital path each year, and go through the thickest part on the same day. If the parent comet has been through recently, there is a fresh, dense deposit of debris, and the shower will be especially good.

The radiant of this shower is the constellation Perseus; that is to say, all the meteors of the shower appear to be emerging from Perseus, radiating out and away from it. But the meteors have nothing to do with Perseus. Instead, we are seeing a kind of optical illusion. Imagine that you are in a car at night, headlights on, driving through a snowstorm. As the snowflakes enter the headlights and you move through them, they appear to radiate from a point in front of the car, seeming to move out from that point and around the car. This is the same effect; it is produced by the Earth moving through the meteoric debris.

So it will be easier to see the meteors if we are metaphorically on the hood of our planet-car than on the trunk! So it is better to observe meteor showers after midnight, because we are now on the forward-facing side in our orbit. The best observing times are from around 2 or 3am until near dawn.

Facing the radiant is not the best way to see lots of meteors, because the trails will be short: the meteors are moving right at you, and the trails will be short and quick. If you look away from it, the meteors are passing by you, and they will have long trails and last longer. So the best way to look is to turn, so your shoulder is pointing at the radiant, or even put your back to it and watch one large region of sky. Then you will see meteors entering the atmosphere at shallower angles, and they will have longer tracks, with more chance to spot them.

FWIW, meteor showers are not hard-edged things. Yes, the shower will have already started, but it is early stages yet, and they won't be very frequent. Your best bet for seeing meteors is a few days either side of the peak, which will occur the night of August 11/12. Also you want to go out AFTER MIDNIGHT. This is because you will now be on the forward-facing hemisphere relative to our orbit.

Wear comfortable clothes, and even in summertime, make sure you have a jacket; it can get rather cool in the wee small hours of the night. You'll be there for a while, so think about a chair, a blanket on the ground, or the like. My preference is for a chaise lounge, because it holds me in a comfortable position for watching the sky. A lap throw or similar blanket might be nice, too, depending on the weather where you are. (If you're in the Southern Hemisphere, it'll be de rigueur. It IS winter down there, after all, Summer Olympics in Rio notwithstanding.)

DO NOT FACE the radiant; this almost guarantees you'll see little to nothing. That's because you're looking right into the direction we're going, so meteor tracks will appear short and swift.

On the night of the peak (and for several days fore and aft), Perseus will be in the northeast. Turn so that your shoulder, or even your back, faces northeast, and survey a large area of the sky looking any direction BUT northeast, and give yourself at least an hour to observe. You should see some nice meteors in that time, especially this year.

Now, according to predictions, the Perseids MAY double their normal rate. But I never say an astronomical event like this ABSOLUTELY WILL do a thing. Because there are no guarantees. Yes, Jupiter may tweak the orbit of the debris so we do plow through the center of it -- but the part we plow through might just be unusually sparse, so it makes no difference.

FYI, I have never heard of the meteors from showers making impact. This is because they are the debris left behind from comets, "dirty snowballs" whose ice has sublimated via solar radiation. All that's left is particulates ranging largely from dust up to grains of sand. Rarely you get something pebble-sized. It all burns up in the upper reaches of the atmosphere, and nothing much gets lower than around 60mi. (Regular meteors can get as low as 50mi. Some get as low as 40. It depends on the speed of the meteor. Perseids usually are gone by a 60mi. altitude.)

SOLAR UPDATE: Sometime between Thursday and Friday, a couple of new sunspot groups formed on the solar near side, 2571 and 2572. They began rather unimpressively, but are now rather reasonable sunspot groups. However, the more active of the two groups, 2572, will be rotating off the west edge to the far side in the next couple of days.

It's a little hard to determine what's going on with the solar far side right now; one of the twin STEREO spacecraft, STEREO Behind, has experienced a "transient hit" -- meaning that the electronics likely took a charged particle hit. Instrument recovery is in work now. The STEREO Ahead craft appears to indicate 2-3 large spot groups may be about to rotate to the near side.

The outflow from a large, oblong coronal hole has enhanced the solar wind in the last few days, resulting in an unsettled geomagnetic field. Another one will swing around into a 'geoeffective' (Earth-directed) position in a few more days, possibly producing more minor geomag storming. I'll post if it does.

ADDENDUM:
Just a quick promo for me and my fellow scientists, for those of you who are interested in such things: A new anthology will be released in September (we hope!) called Science Fiction By Scientists. Every short story in it is "hard SF" written by an actual scientist, along with a quick primer at the end of each story on the science involved. It's available for preorder now!

~Stephanie Osborn
http://www.stephanie-osborn.com

Solar Activity and the Activity Indices

Okay, back to bar magnets again. Because the Earth has one. But of course it's three-dimensional, not like our iron filings on paper example. Imagine picking up the bar magnet with the iron filings and paper attached, and rotating it 360º, letting the iron filings remain in the areas they move through. Now you have an image of what a three-dimensional dipolar (2-pole) magnetic field looks like – sort of like a giant pumpkin. With the solar wind (which is probably the largest influence on the interplanetary magnetic field) pushing on it from the Sun direction, the side of the pumpkin facing the Sun tends to smush in, but the side away from the Sun tends to stretch out and form a long tail. (You can see a really good animation of how this works here: http://en.wikipedia.org/wiki/File:Animati3.gif) This is all to say that you HAVE to think of the geomagnetic field three-dimensionally. And if it is three-dimensional, then each part of the field has an x-, a y-, and a z-coordinate component.

Let's simplify for a minute. Let's say that we're going to look at the component of the geomagnetic field that is running horizontally to the Earth's surface at any given point. Now because the Earth is curved, this is a tangent line that is continually changing as you move around the Earth. Now let's look at the disturbances from normal, caused by solar weather – coronal holes, CMEs, what have you.

So we have these variations, that are going to be different for different parts of the Earth for the same event. How do we measure it? It's a little like a Richter scale for geosolar storms. It runs from zero to nine, and there's a special formula that enables it to be calculated regardless of the location of the observatory, just like the Richter magnitude of a quake can be determined from seismographs on the opposite side of the globe. This scale for solar-induced geomagnetic activity is called the K-index. Zero is essentially no activity; anything above 5 is considered a storm level of activity. The bigger the number, the greater the effects seen on the ground, and the farther south the auroral oval can be seen. At a K=9, the aurora can be seen...in the TROPICS.

(Just for the sake of more information, the letter K was derived from the German word “kennziffer,” which apparently means “characteristic number.” Us scientists, we love our imaginative names, you know?)

Now if we reference the Kp index, we're talking about the interplanetary K index, not the geomagnetic K index. This is an average of all the K indices from all of the observatories, weighted as appropriate (remember, you won't get the same measurements from the various observation sites, so you have to factor that in, as well as the fact that the geomagnetic field is constantly changing). This gives us an indication of what the interplanetary magnetic field (IMF) is doing. BUT – not all of the stations report in at the same time. So then scientists have to calculate something called the “estimated Kp” which is just what it sounds like – an estimate for those stations that haven't reported in yet. This can sometimes be a very good predictor of what the magnetic field is going to do, and sometimes not so much. We're still very much learning this particular science.

But we're not done with indexes. There's also something called the a index. This is based on the AMPLITUDES (yep, there's the reason for using an a) of the deviations from geomagnetic normal, taken over a three-hour period. Then there's the A index, which is an AVERAGE (yep, that's where the A came from) of all the a-indices for a 24-hour period.

One more index we need to look at is the G scale, which is the National Oceanic and Atmospheric Administration's (NOAA) way of quantifying the strength of the geomagnetic disturbance. For any K index of 4 or less, the scale shows G0. At K=5, we jump to G1 – minor storming. For K=6, we have G2. For K=7, G3. At K=8, we have a storm level of G4, and at the maximum K=9, we have maximum storming of G5. Think of it like the Earth's solar DefCon level.

Next week we'll go into those DefCon levels in detail.

-Stephanie Osborn

http://www.stephanie-osborn.com

My husband is a keeper

by Stephanie Osborn
http://www.stephanie-osborn.com

I just returned from Libertycon, one of several major SF conventions in Chattanooga TN. There, I was delighted to be this year's Science Guest of Honor. These are good people, down-home, loving and friendly. As usual, they not only ran my standard bio in their program book, they also asked some people to give them their stories about me. Due to some crossed wires, they got two: one from my good friend Sara Harvey, and one from my husband, Darrell Osborn.

Now, Darrell and I have been married quite awhile, and like most married couples of long standing, we know we love each other and that's that. The busyness of life and the knowledge of belonging - as well as some reticence on both sides to be able to say the things that we feel deepest - means that the knowing is felt, not said.

Until the convention. And then my dear husband laid it all on the line for everyone to see. And I am so proud I can't stop reading it. So I'm going to share it with the world:

Let's start at the beginning. Decades ago, before many of you were born, my friend Danny and I were walking through the theater building on the campus of Austin Peay [State University] in Clarksville, TN. We were passing through the "Green Room" on our way to the stage when we saw an attractive blonde sitting on the couch. We looked at each other and then did what any red-blooded theatre geek would do. We hit on her. That was the first time I met Stephanie Gannaway. She was finishing her last year at APSU and preparing to graduate with a triple major in Math, Physics, and Chemistry. She was also picking up minors in Geology and Computer Science. My first thought was, "At last, someone I can talk to."

Fast forwarding a couple of years finds us married and living in student housing on the campus of Vanderbilt in Nashville. Stephanie was working on a Masters in Astronomy and I was creating havoc in the Live Entertainment Department at Opryland [back when it was a theme park -Steph]. One day word came down that Carl Sagan was coming to give a talk. You've got to remember, at this time Carl Sagan was a science rock star. Everyone knew "Cosmos" and he was a regular on Carson's Tonight Show. We later find out that Max, one of her professors, and Sagan were college buddies. The talk was great and we went to reception afterward. We progressed through the greeting line until we reached Max and Sagan. Max introduced Stephanie as one of the two astronomy graduate students. As Stephanie shook his hand, Max leaned over and whispered to Sagan, "She's one of the good ones." Sagan gave a knowing little smile and nod. That was our Sagan moment. Although brief, I think that short phrase and nod meant more to her than any of the degrees she had gotten.

A few decades have passed and so has Sagan. Now Stephanie has moved from science and her involvement in the space program to its symbiote science fiction. I have no doubt that the time will come again when she will stand before some sci-fi writer rock star and once again hear the words, "She's a good one." (That reminds me of the time we ran into Ray Bradbury; a story for another time.)

Last year I re-connected with Danny. He's now an Associate Dean at the University of Memphis. That's a great accomplishment, but I got the girl.

-Darrell "Doc" Osborn

Yep. I always knew Darrell was a keeper. <3

-Stephanie Osborn
http://www.stephanie-osborn.com