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Fire in the sky: Urban astronomer explains annular eclipse

On May 20th the moon will pass over the sun creating a ring of fire” or an annular eclipse // Wikimedia Commons

It’s only once a year that you can experience almost complete darkness in the afternoon sky. This Sunday, the Western United States will experience a solar eclipse. But in a special path across Northern California, the moon will be almost fully enclosed by the disc of the sun, creating a “Ring of Fire” effect. To learn more about the science behind the spectacle – and another reason to look up later in May – KALW's Ben Trefny talked to our local expert, Paul Salazar. Salazar is a member of the San Francisco Amateur Astronomers and keeps a regular astronomy blog.

PAUL SALAZAR: We get to have a very beautiful alignment of the sun, the moon, and the earth in which the disc of the moon as its covering the sun will appear fully engulfed in the body of the sun. We have partial eclipses – those are more common – and in fact, when this happens on May 20 there will be a partial eclipse visible from San Francisco. In our case here in the city it will about a 90 percent eclipse, which is pretty good – it's going to be very much a little thin crescent sun left behind and most of it covered by the moon.  But when you have this unusual alignment if you travel a couple hundred miles north of here to the Shasta and Redding area or let's say out to Reno, there you're going to see the full annular effect where the moon appears to be encircled by the sun.

BEN TREFNY: So what does that photosphere of the sun look like on the outside? Because if it was really a ring of fire I could see flames shooting out or maybe and exaggeration of it…

SALAZAR: Yeah, I guess a “ring of fire” is maybe over marketing the event, right? Because you're not going to see flames shooting out the side. It's just going to be an absolutely brilliant ring edge. Now through specialized telescopes that allow you to see those little flames if you will – what are called prominences – shooting out the side of the sun’s limbs. It takes about an hour and fifteen minutes from when the moon touches the edge, it's called first contact, to all the way at the deepest part of the eclipse. It's a gradual process and a wonderful thing to watch. There's different stages of it. From first touch to the middle to the last touch takes about two and half hours.

TREFNY: So this annular eclipse, the best viewing will be north of the San Francisco Bay Area, but what are the very best nearby viewing sights, would you say, all things considered?

SALAZAR: If you just go up Interstate 5 or Interstate 99, there's going to be a lot of places up by Redding, up by Shasta just north of Chico would be a pretty good spot. Just into Lassen National Park would be excellent. The shadow of the moon cast down moves across the earth and it moves in a southeasterly pattern in this case, some places like Reno, Nevada would be quite good. The only other factor you have to really think about is weather, because obviously you want to go somewhere where you have an extremely high likelihood of clear skies and also where you can look straight to the west. This is going to happen late in the day. It's going to have that first contact at about 5:15 in the afternoon and it's going to reach that peak at roughly 6:30 p.m. So you've got to have a spot where you can look to the west, there aren't mountains, hills or other sorts of natural issues to worry about. And you've got to have crystal clear skies.

TREFNY: So maybe not the San Francisco Bay Area, then?

SALAZAR: It's really risky, yeah. I'm headed north. We're going up to the Shasta Resort.  We've put together – now I'm speaking on behalf of the San Francisco Amateur Astronomy Club – we've put together a road trip, we're calling it the Ring of Fire Road Trip and we're all packing our bags and heading north for the day and we going to set  up shop in the Shasta area. And it's open to the public, people can go to the San Francisco Amateur astronomer's website and sign up online. No cost, you just show up, take part, they'll be some speakers giving talks in advance, and we'll have some mini telescopes out there, and it will be a chance to be with a crowd. I've been to several eclipses, and I've found it to be much more fun with a big group. But I do want to talk for a moment about safety.  A solar eclipse is a dangerous thing if you aren't prepared for it. And you really do have to take a moment to prepare by purchasing or somehow acquiring a safe solar filter. And that's not just a bunch of sunglasses stacked together or old film or something like that. Those are not safe. You need something that is really designed for staring directly at the sun. And you can buy that, there's a great shop in San Francisco called Scope City. There's a guy named Sam that I know very well, he runs the place, and he's got hundreds of pairs of these glasses. And they're cheap: we're talking three or four dollars for a pair of cardboard glasses that it's going to be safe to stare at the sun. But it's worth the time and effort now to equip yourself so when the big day comes, you can enjoy it!

TREFNY: Cardboard glasses, so how does that work?

SALAZAR: Well, cardboard glasses, you know, it's not quite like what they have in 3D movies – it's just a little disposable glasses with a little Mylar piece in the middle that's been properly equipped to cut down on the brightness of the sun to a safe viewing level.

TREFNY:  Is it possible to make one of those yourself?

SALAZAR:  Again, I would be very suspect. The glass part is the most important thing, or the Mylar sheet. For example, you can use welder's glass but you have to get what's called a shade 14. It's what arc welders use, which apparently is a bright as the sun.

TREFNY: So you could put on one of those welder's masks?

SALAZAR:  You absolutely could, and you'd be totally safe then.  You wouldn't even get a sunburn. That's the best way to see it.

TREFNY: I should just wear one of those all over the place.

SALAZAR: Everyday, it would be kind of a novel thing here in the city.  But seriously, you really do have to think about that, prepare for it. There's some good online resources, you could order them online right now. As the day of the eclipse draws nearer, it might be harder to get them delivered on time.

TREFNY: But regular sunglasses are not sufficient.

SALAZAR:  Definitely not, no. What happens is the sun is, besides the extreme intensity in brightness, the sun is also sending infrared rays, and if those are not properly filtered then those are going to warm the inside of your eye and it really does give you permanent damage.  It's an extremely serious thing.  So when you do see an eclipse as beautiful as it is, you have to do it under the right circumstances, with the right equipment.

TREFNY:  What do you think it is? What's done to the human soul to see a celestial even like this?

SALAZAR:  There's such a broad range. There's an entirely separate group that's meeting at the Shasta Resort along with us astronomy geeks. And they are there purely for the spiritual experience of being in the shadow of the moon. And I'm interested in what they have to say about it as much as I'm interested in them coming to hear what we have to say about it when we're all there together – kind of two groups colliding in the same cosmic spot with good reason, because we're all there to see this thing happen in the sky that preordains that if you stand in the right spot on May 20 than the shadow of the moon with pass over you. I think it's a profoundly moving experience. 

Ben was hired as Interim Executive Director of KALW in November, 2021.