This weekend, spectators in the Western Hemisphere are in for a special treat when the moon moves in front of the sun, blocking sunlight and creating a fantastic “ring of fire” in the sky. This is an annular eclipse, not to be confused with a total solar eclipse, as we’ll have one of those soon enough.
Here to speak on this rare solar viewing event and how best to witness it safely, is Nasa expert and Heliophysics Research and Analysis Lead, Patrick Koehn.
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PK: Hi, thanks for having me on.
WAMC: Patrick, thank you for joining us. We're speaking to you now from NASA's Goddard Space Flight Center in Maryland. What is it you primarily work on there?
PK: My job is primarily to enable science. I don't actually do science anymore. That was in a previous lifetime, but now I oversee the evaluation of proposals and a number of other activities. I also am the liaison with the IMAP mission, which is an upcoming mission that's going to launch in late ’20, no sorry, early ’25 now. Also, for the Voyager mission, which has been in the news a lot recently. So, I'm a busy person, I have a lot of stuff going on.
WAMC: And so, this weekend there'll be an annular solar eclipse. What does that mean, exactly? And what can we expect to see?
PK: So, an eclipse happens when the disc of the moon slides, when the moon moves between the Earth and the sun in such a way that it completely blocks the surface of the sun. Now in an annular eclipse, the moon is a little bit farther away than it ordinarily might be, it's actually at apogee, so it appears smaller in the sky. So, it doesn't completely cover the disk of the sun, it sort of slides across the middle. So, it blocks the light coming from the middle of the sun and what's left behind is this ring of very bright light, this ring of fire. So, it's called a ring of fire or eclipse, or an annular, or “ring like“ solar eclipse.
WAMC: Here in New York, and on the East Coast, we're outside of the path for the annular eclipse, but we'll still see a partial eclipse, can you tell us about what viewers might expect to see?
PK: Okay, if you happen to be in the eclipse path, you'll see the annulus, you'll see the annular solar eclipse. If you're not in the eclipse path, and this is going to be anywhere in the contiguous 48 states, and actually parts of Hawaii and parts of Alaska, you'll be able to see it as well, they'll see what is called a partial solar eclipse. And in that case, the moon rather than sliding through the middle of the sun, it actually slides across the edge, and it sort of looks like the moon is taking a bite out of the sun like you take the bite out of a cookie. And depending on how far away you are from the eclipse path, you'll see either more or less bite, you'll see a big bite or a small bite. Here in DC, and as well as in New York, I think it'll be a relatively small bite. It's on the order of 25% or so coverage. So, it's a small bite, but it's still going to be a spectacular event.
WAMC: One might think that with a large percentage of the sun covered that it could be safer to view. But this isn't true. How can viewers safely see this annular eclipse?
PK: Yes, safety is really, really important anytime you're looking at the sun safety is of utmost importance. Because if you look at the sun with unfiltered lenses, or through regular sunglasses, or with the naked eye even, too much light is going to be focused on into the eye and it can cause serious, serious damage to the eyes, and that damage is almost instantaneous. You might not notice it for a couple of hours or so. But it's really important that if you're going to be looking at the Eclipse, if you're going to be viewing the eclipse directly, that you do it with these special solar viewing glasses that you can pick up. A lot of public libraries have them, some museums will have them, they're available here and there. If you can't get a hold of these glasses, you're not out of luck, you can still witness the eclipse, but you won't want to look at it directly. If you don't have the glasses, you could take a piece of paper or an index card, anything you happen to have handy, and poke a hole in it. Hold it up above the sidewalk, or a second sheet of paper, or something like that, preferably with the sun behind you just for extra safety. And that hole in the piece of paper projects an image down onto the screen, whatever screen you happen to be using. It's a pinhole camera. And using just that simple hole in a piece of paper, you're actually able to see the eclipse. If you don't have a piece of paper, you can actually make a little hole with your fingers. You can hold your fingers together and hold that little hole over your hand, over the sidewalk or something like that, and still view the eclipse. My favorite way to view the eclipse though, if I don't have these solar viewing glasses, is to find a tree and stand under it. Because the little spaces in between the leaves actually create this web of individual little mini eclipses that are moving around. It's an amazing experience.
WAMC: This ring of fire eclipse is the first of two solar eclipses that we in North America are in a great position to see. Can you tell us about the big eclipse happening in April of next year, and how it will be different than what we're seeing today.
PK: The one coming up in April is actually a total solar eclipse. And if you happen to, again, if you happen to be in the eclipse path, you'll actually see the disk of the moon completely cover the disk of the sun. And when that happens, what's left behind is the wispy outer atmosphere of the sun which is only visible from the surface of the Earth with the unaided eye during one of these total solar eclipses. So, it kind of looks like the sun has bed-head. You have these jets of material that are coming off the sun that are visible during this particular event. It's an amazing experience. We've got the total solar eclipse in April, and then in 14 months from now, this isn't an eclipse coming up but we're going to be ending our festivities that we're calling the Heliophysics Big Year with the passage of the Parker Solar Probe, which is the fastest spacecraft ever built by humans. It is going to be dipping down into the sun's atmosphere and actually sampling the material there, and taking a whole bunch of other measurements as well. So, it's a 14-month period that begins tomorrow, and then extends through December of 2024. We're trying to get the public out and really engaged in observing the sun and seeing how the sun impacts our daily lives. We have a number of citizen science opportunities that are going on throughout the year. I encourage folks to check out on the web go.nasa.gov/eclipse. For more details, there's lots of information there.
WAMC: And in thinking about that, what kind of impact does an eclipse have on the earth itself?
PK: There's two levels to that question. There's the scientific level and the personal level. On the scientific level. Of course, the temperature of the atmosphere goes down a bit, but also there's a layer of charged particles in the upper atmosphere called the ionosphere. And that ionosphere is maintained by solar radiation. Sunlight comes in and ionizes or strips away the electrons from the gases in the upper atmosphere. And so, during an eclipse, we expect the ionosphere to change quite a bit because all of a sudden, its energy sources cut off. So, we have a couple of rocket launches going on for the Eclipse. We're going to be launching a rocket from White Sands Missile Range just before, during, and immediately after peak Eclipse. And looking at how the ionosphere changes, both before, during, and after the eclipse. We've also got amateur radio operators that are going to be studying how radio wave propagation changes during an eclipse. Because it's the ionosphere that actually controls how radio waves bounce through our atmosphere. So, we have a lot of good science stuff going on. But on a personal level and on an individual experience level, eclipses are a singular moment in time, really. Because as the moon obscures the sun, of course, atmosphere, the temperature around you, the air around you starts to feel a little bit cooler. Of course, the lighting goes down significantly, and animals think it's bedtime. So, birdsong actually changes during an eclipse. Animals start to head for their homes and go to bed. There's something truly magical about just observing and witnessing an eclipse firsthand. So, we're really hoping that people take the time and have the opportunity to go out and just be in it.
WAMC: Eclipses happen fairly often. How is it that viewing them is increasingly so rare?
PK: I mean, the earth is 75% covered by water, right? So, and yes eclipses happen regularly, but most of the time they happen over unpopulated areas. So, it is indeed a rare thing when an eclipse happens over, you know, major cities. So, these eclipses do happen all over the planet at regular intervals. This is something that it's easy to predict when these things are happening, but it's not so easy to see. Because you have to be in exactly the right place at exactly the right time to get the full effect. The next total eclipse is April 8, and 2024. If you happen to be lucky enough to live in the San Antonio, Texas area, you get to see both, but most of us are not that lucky. And then the next one after that isn't for another 40 years or something. So, this really is your next best chance to see this.
WAMC: Patrick, thank you for taking the time to join us today. Any final thoughts on this weekend's Eclipse or the upcoming total eclipse in April?
I cannot emphasize enough how important it is just to get out and experience this. Now NASA has, of course, lots of programs throughout the next 14 months, you can check out the website, we've got a live stream going on NASA TV to further sort of enhance the experience. But really, I encourage people just to go out and witness this. These things don't happen very often. I know, the one event that's coming up in April will be my very first total solar eclipse that I've actually been in the right place at the right time to see. So, it's really important just to get out and be in it to experience this firsthand.
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That was Patrick Koehn, NASA's Heliophysics Research and Analysis Lead. For WAMC News, I'm Jody Cowan.
