solar eclipse

All posts tagged solar eclipse

Last night, I visited the town of Stanley, a small tourist spot so lovely every view looks like a postcard. Since Stanley is smack in the middle of the eclipse track, and so they are anticipating tens of thousands of visitors in August.

At the invitation of Sarah Cawley of Sawtooth Interpretive and Historical Association, I spoke at the Stanley Museum to a crowd of nearly 100 about the eclipse.

As usual, folks asked some brilliant questions, including the classic “Why does the Moon move west to east during the eclipse, instead of the usual east to west motion?“.

The answer (which I tried to demonstrate by spinning on my axis) is that the Moon’s motion during the eclipse involves both the Earth’s rotation – that causes the Moon and Sun to move together east to west – and the Moon’s orbital motion – that causes the Moon move west to east relative to the Sun.

After the presentation (posted below), my hosts and I adjourned to the Redfish Lake Lodge, where I enjoyed the grilled trout and one of my hosts attempted to teach me to fold a napkin flower. I have to admit that the trout came out much better than my flower.

UPDATE (2017 Aug 2) – I’ve had more than person ask whether they’ll be able to see the solar corona, the tenuous and very hot outermost layer of the Sun’s atmosphere, during the partial eclipse in Boise. I believe the answer is no.

This website indicates that the corona is a million times dimmer than the Sun’s photosphere. During the darkest part of the partial eclipse in Boise, the photosphere, the part of the Sun we usually see, will be 200,000 times dimmer than usual (see below).

So my guess is, from Boise, not enough of the photosphere will be occulted to reveal the corona.

Millions of people will travel from around the world to observe the total solar eclipse on August 21 in the path of totality, a band extending across the US in which the Moon will completely occult the Sun. Everyone NOT inside that path will observe a partial solar eclipse, and the closer you are to the path of totality, the darker your partial eclipse.

During our statewide tour talking about the eclipse, I have been asked again and again “Is it worthwhile trying to get to the path of totality?” The honest truth is that there are some aspects of the eclipse that you will miss out on if you don’t get to the path of totality.

BUT getting to the path of totality can be difficult – in Idaho, there are reports that all hotels and campsites are booked up, and driving to the path on the day of the eclipse will probably involve sitting in traffic for many hours. So travelers should be prepared with food and water.

So what will you see if you CAN’T get to the path? You can still enjoy a nice eclipse, but you MUST use eye protection during the ENTIRE eclipse. Staring at a partial eclipse at any level can permanently damage your eyes.

Eclipse shades, the best way to safely observe the solar eclipse.

What will you see during a partial eclipse? That depends on where you observe from. For example, Boise is just south of totality and will see a partial eclipse with 99.555% obscuration (check out this amazing map to see eclipse conditions anywhere in the world). That means the Moon will block all but 0.00445% of the Sun’s disk, making the Sun more than 200,000 times darker than usual.

So what will that look like? The visualization below shows an approximation as seen through eclipse shades. As one-two-hundredth its normal brightness, the Sun will appear a little dimmer than the sky at twilight* and about ten times as bright as the Sun normally appears from Pluto.

What a 99% partial eclipse looks like through eclipse shades. From

At this level, though, you probably won’t be able to see the solar corona, and other eclipse effects will be substantially more muted. But for those who can’t take off of work or skip school – August 21 is a Monday, after all – the partial eclipse viewed from near the path of totality will still be a once-in-a-lifetime event.

*At 0.00445%, the usual solar flux (1300 W/m^2) will be reduced to about 0.06 W/m^2. This paper indicates that when the Sun is at a zenith angle of 105 degrees (i.e. a while after the Sun has set), the sky brightness is about 0.1 W/m^2.

Along with my student Karan Davis, I enjoyed a visit last night to the town of Cambridge, about a two hours north of Boise, to talk to folks there about the August 21st solar eclipse.

We were invited by Nina Hawkins, one of the librarians at the public library there in town, and we met her before the presentation at the newly refurbished Country Coffee Cabin in Midvale.

A BLT and fingersteak basket later, Nina led us up the nine-mile winding road to Cambridge, where we were greeted by a few dozen Cantabrigians at the library. For about an hour, Karan and I described the upcoming event and answered questions from the public. As always, I was impressed by how engaged and interested everyone was, especially late on a Thursday evening.

After passing out eclipse shades to the attendees, we packed up our road show and drove back down to Boise, just as the Sun set in the cloud-strewn pink sky, a preview of the twilight effect we will experience during the eclipse in August.

The presentation I gave in Cambridge is posted below.

Sunset over Idaho Falls.

Just returned from my trip to Idaho Falls, speaking to hundreds of locals about the upcoming eclipse.

I was invited to give two presentations at the Idaho Falls Public Library, a library so beautiful and spacious it has an atrium with a fountain.

On Tuesday evening, I gave a presentation to the broader Idaho Falls community. A few minutes before the presentation, there were only about a dozen attendees, which made me a little nervous, but by the appointed hour, the space had filled beyond capacity, with nearly one hundred folks – an unexpected large but very welcome crowd.

Before my next presentation on Wednesday afternoon, I took a side trip up to the St. Anthony dune field. Since the dune field is likely to be a prime spot for eclipse-viewing, I was curious to see what preparations they were making.

The dune field near St. Anthony.

Back to Idaho Falls for an afternoon presentation geared to the youngest eclipse enthusiasts. Here again, we had an unexpectedly large crowd, with easily 200 kids and parents cheerfully crammed into the presentation space.

Wednesday’s crowd.

After helping the kids make souvenir planispheres, I packed up my roadshow for the long drive back to Boise. The megaflood-carved landscape of the Snake River Plain combined with a Planet Money podcast about a flatware-crafting commune to make the time pass quickly.

The presentations I gave in Idaho Falls are posted below.

Idaho Falls Community Presentation

Idaho Falls Children’s Presentation

UPDATE: The stargazing event today went swimmingly – several dozen visitors came down to talk about the solar eclipse and look at the Sun. We even had crew from KTVB film some interviews. Some photos from our event below.

Join the Boise State Physics Department and learn more about the Aug 21 solar eclipse. We will host a conversation about observing the eclipse and distribute eclipse shades.

The event will take place on Sunday, June 18 from 12p till 2p in the plaza just north of the Multipurpose Classroom Building on Boise State’s campus.

Questions can be sent to Prof. Brian Jackson via e-mail –

A quick visit last night to a city council meeting in Payette, just about an hour northeast of Boise. I gave a short presentation about the eclipse (below) and helped answer questions for the council and city residents, along with reps from Idaho’s Board of Tourism and Emergency Management.

One particular concern for Payette is traffic on the day of the eclipse. Lots of folks are expected to fly into Boise and the surrounding area for the eclipse and then drive up to the path of totality, which will take many of them along Hwy 95 and through Payette. City fire and police reps are trying hard to plan for any eventuality and seemed well aware of the unprecedented event headed their way.

Unfortunately, I was only in town for a few hours, so not any time to poke around. Maybe next time.