Double rainbow in my neighborhood at dusk, 14 Sept 2017 (photo by Kate St. John)

Last Thursday evening my husband and I were treated to a gorgeous double rainbow with parallel color bands under the main arc.  What are these wonders and what causes them?

First, some fascinating basics: Rainbows are caused by light hitting water droplets and being reflected, refracted and dispersed by them:

• Reflected from both the outside face of the water drop and its inside wall.
• Refracted or bent as it enters and exits the raindrop.  Refracted twice!
• and Dispersed from white light into seven colors: red, orange, yellow, green, blue, indigo and violet.

We saw the rainbow at dusk while the sun peeked below rain clouds and were surprised we could see the entire arc. Only those located at the geometric center of the rainbow, the antisolar point, can see it end to end.

Rainbow panomara (photo by Rick St. John)

Have you ever noticed that the sky under the rainbow is brighter than the sky outside it?  True!  Click here for an explanation (fourth paragraph).

And then there’s the fancy stuff: the double rainbow and the extra bands under the arc.  To illustrate them I’ll use this photo from Alaska that shows all of the features at the same time. Click on the image to open a high definition version in a new window and see them up close.

Double rainbow and supernumerary rainbows on the inside of the primary arc, Wrangell-St. Elias National Park, Alaska (photo by Eric Rolph via Wikimedia Commons)

Double rainbows happen when light bounces twice inside the raindrops before it exits.  The light goes inside, reflects off the back wall, reflects off the front wall, and then exits.  Double rainbows are parallel to the main rainbow, are not as bright, and their colors are reversed — red-to-violet instead of violet-to-red.  I never noticed that. I’ll have to watch for it next time.

The faint color bands just under the main rainbow arc are called supernumerary rainbows.  Wikipedia says they cannot be explained using classical geometric optics but they occur when the water droplets are less than 1 mm in diameter.  Fancy rainbows are complicated!

And finally, the end of the rainbow. From our vantage point it was in front of that tree on the horizon.

End of the rainbow in my neighborhood, 14 Sept 2017 (photo by Kate St. John)

Irish legend has it that leprechauns hid their pots of gold at the end of the rainbow. I wonder whose house was there.

Rainbows move away as you approach.  There’s no way to know.

(photos of neighborhood rainbow by Rick & Kate St. John. Alaskan rainbow by Eric Rolph via Wikimedia Commons)

Visualization of Hurricane Irma wind, 10 Sept 2017, 5am (screenshot from the “earth” wind map)

On Friday afternoon I checked in with my brother while he and his wife prepared for Hurricane Irma at their home in Boca Raton.  Located west of I-95, his neighborhood wasn’t part of the mandatory evacuation order.  Everyone was getting ready, then they’d throw a “good luck” party Friday night and hide indoors until the storm is over — probably midday Monday.  They were all hoping that Irma would go west, and that’s what she’s doing.

Concerned for my friends and relatives in Florida I’ve been monitoring Hurricane Irma on the National Hurricane Center’s website at www.nhc.noaa.gov.   My brother suggested watching the wind at windy.com and that reminded me of the similar “earth” website.

Watch the wind at these links, centered on Marco Island, Florida along the path of the storm.

• windy.com provides current conditions and 10-day forecasts by location. Here’s Marco Island at windy.com.
• “earth” at nullschool.net provides a visualization of weather patterns on the entire globe. Click here or on the image above to see the Marco Island area.

Move the map around and you’ll see strong wind blowing onshore toward Georgia.  That’s why there’s a storm surge warning in Savannah.

There’s one thing these maps can’t show.  Hurricanes spawn many tornadoes but they don’t appear on the wind maps.  Right now there’s a tornado watch in Boca Raton until noon on Monday.  Yikes!

(screenshot from earth.nullshool.net on 10 Sept 2017, 5am. Click on the image to see the current wind map)

UPDATE:  At 11:30pm on Sept 10, my brother reports that they are OK at home in Boca Raton.  The power went out for eight hours but came on around 11pm. They’ll go outside Monday morning to see what happened to the landscape.

8 September 2017, 10am EDT:

Many of us are watching with morbid fascination as Hurricane Irma churns through the Caribbean on its way to Florida.  Even if we aren’t in Irma’s path, we know people who are and we’re worried.

After Irma passed over the U.S. Virgin Islands (USVI) I searched the Internet for footage of St. John, USVI, where I visited in January 2015.  I found information in this USA Today article with links to the USVI Hurricane Irma Alert Facebook page.  Beyond the obvious human suffering, I am struck by how brown the landscape is now.  All the leaves were blown off the trees.

Where are the birds?  What did they do during the storm?

Fortunately birds have strategies for coping with bad weather including:

Shelter in Place

Like us, birds hide out of the wind and rain and wait for the storm to end.  They use man-made structures, thickets, and deep valleys where the wind is less intense. Their strategies are described here in Shelter From The Storm.

Pigeons sheltering from heavy rain (photo from Wikimedia Commons)

Evacuate

Birds can sense when a storm is coming and often evacuate before it strikes.  A study of golden-winged warblers found that they left Tennessee a day ahead of a tornado: Warblers Fled Tornado One Day Ahead.  Land birds in Florida can move northwest as Irma approaches but the birds on Caribbean islands had nowhere to go.

Fly In the Eye of the Storm

Sea birds have a third option.  As they fly in search of a calm spot, they end up in the eye of the hurricane where they travel with the storm until the winds die down.  This NASA image shows that the eye of Irma on Sept 5 was larger than both Anguilla and St. Martin so it was probably a relatively safe place.  However, the hurricane won’t lose power until it’s over land so the sea birds may be exhausted when they finally stop far inland.

The eye of Hurricane Irma passing over Anguilla and St. Martin, 5 Sept 2017 (image from NASA Sport)

People and birds in the path of Hurricane Irma are all getting ready.  I think of my friends and family in Florida.

For more the latest information on current hurricanes, see NOAA’s National Hurricane Center.

(photo credits: Hurricane Irma satellite animation from NOAA, photo of pigeons sheltering from Wikimedia Commons, photo of tornado from Wikimedia Commons, Eye of Hurricane Irma from NASA Sport. Click on the images to see the originals.)

Composite of total solar eclipse in South Carolina, USA, 21 August 2017 (photo by Herm Donatelli)

Blog reader Herm Donatelli traveled from Atlanta to South Carolina to witness the total solar eclipse on Monday August 21.

He equipped his camera with a filter so he wouldn’t damage it.  “I unfortunately forgot to remove my solar filter during totality,” he wrote, “and thus had no pictures of my own during that time. That’s what makes the composite so realistic!”

Here’s his rendering of the eclipse in time.

(composite eclipse photo by Herm Donatelli)

Two birds roosting, mallard and European coot (photo from Wikimedia Commons)

How will birds and animals react to the solar eclipse on Monday, August 21?  Will they act differently during the total eclipse (from Oregon to South Carolina) compared to the partial eclipse here in Pittsburgh? You can help Science answer these questions.

We have anecdotes about animal behavior during solar eclipses but not a lot of scientific data.

People have noticed that birds stop singing, farm animals return to the barn, and night critters wake up.  Are they reacting to totality as if it’s a miniature night?  Or is it something else?

Science doesn’t have answers because the data has been hard to collect.  To reach a conclusion, the scientific method gathers data over and over again under the same conditions.  It’s hard to do for total eclipses because in any one location they occur as much as 400 years apart.

Scientific method diagram; Knowledge is Gained (image from Wikimedia Commons)

But this time will be different. On Monday August 21, thousands — or even millions of us — will collect data on animal behavior before, during, and after the eclipse thanks to the Life Responds: Solar Eclipse 2017 project and the iNaturalist app. The project will analyze our data and repeat the experiment during the next eclipse.

Here’s how you can help.  (Instructions are from the Life Responds: Solar Eclipse 2017 project.  Click the link for more information.)

Before the eclipse. Day(s) ahead of time.

1. Download the free iNaturalist app to your Android (Google Play) or iPhone (App Store)
2. Open the app and create an account at iNaturalist.org
3. Practice using the app. Here are some instructions.
4. Inside the app, join the Life Responds project
5. Decide where you’ll be observing the eclipse and know when it’ll be at maximum darkness.

On the Day of the Eclipse:

1. When you get to your observation site, choose the birds and animals you’ll observe.
2. Post at least 3 observations of the birds/animals in iNaturalist at the times below. Add anything interesting you notice in the Notes.
   1. 30 minutes before maximum darkness.
   2. During maximum darkness or totality
   3. 30 minutes after maximum darkness.
3. Make additional observations if you wish.

The cool thing about this project is that you don’t have to be in the path of totality to provide useful data.

Do the birds stop singing at dark and restart when it’s light? (This is a trick question! Few of them sing in August.) Do the chimney swifts dive into chimneys to roost?  Do the squirrels go to bed?  Do the deer come out?  What about your pet?  And if you’re a beekeeper, how are your honeybees?

I’ve downloaded the app and I’m ready.  I sure hope it isn’t cloudy on Monday, August 21!

(photo from Wikimedia Commons; click on the image to see the original)

p.s. Observing Machines:  If you’re in a city in the path of totality, the street lights will come on.  Will they come on in Pittsburgh?

Map of the Total Solar Eclipse on 21 August 2017 (image from eclipse2017.nasa.gov)

By now I’m sure you’ve heard …

Two weeks from today on 21 August 2017 there will be a total eclipse of the sun across the United States.  The moon will pass between Earth and Sun, casting its shadow on our continent.

In a narrow band 70 miles wide, from Oregon to South Carolina, the sun will disappear completely for about two minutes. Folks eager to witness the total eclipse have made plans to visit sites in its path including Nashville, TN and Charleston, SC.

Pittsburgh will see only a partial eclipse but there will be plenty to watch. The moon will move across the sun from 1:10p to 3:55p with maximum coverage resembling the crescent below at 2:35p.  Don’t watch without special glasses and, for your scope and camera, special filters!  See below.

Mockup of partial eclipse at maximum as it will be seen in Pittsburgh on 21 Aug 2017 (image from Wikimedia Commons)

Where to watch the eclipse in Pittsburgh, 21 August 2017 … some of the many locations.

• On your computer: See the entire eclipse from coast to coast on NASA’s Eclipse Live Stream. The shadow begins in Oregon at 9:04a PDT (12:04p in Pittsburgh) with totality from 10:16a PDT (1:16p here) to 2:48p in South Carolina.  You don’t need filters to watch online.
• At Carnegie Science Center: The weather won’t matter at Carnegie Science Center. Outdoors, watch through special solar observation equipment.  Indoors at Buhl Planetarium. Click here for info & directions.
• Sidewalk Astronomy: Weather permitting 1:30p to 3:00p outside the Staghorn Garden Cafe, 517 Greenfield Avenue, Pittsburgh, 15207.   John English will set up his scope to project the sun’s image on the wall so you can watch its shadow without looking at it.
• In your own backyard:  Prepare in advance! Read Eclipse2017: Who, What, Where, When and How and get …

Special solar eclipse glasses, filters or pinhole viewers to watch the solar eclipse.

Don’t risk going blind or damaging your camera or scope by viewing the eclipse without protection! Click here for NASA’s list of safe viewing methods including solar eclipse glasses, pinhole viewers and filters for your equipment + how to use them.

Solar eclipse glasses are inexpensive (only a couple of dollars) at the Carnegie Science Center Gift Shop or online but only buy from reputable vendors listed at American Astronomy Society! Sunglasses and fake glasses won’t protect you.

Here’s an example of the real thing from B&H Photo Video on the reputable vendor list.

Lunt solar eclipse viewing glasses from B&H Photo

I hope it isn’t cloudy on Monday August 21!

(photo credits: Click on the images to see the originals. Globe from eclipse2017.nasa.gov. Partial eclipse image from Wikimedia Commons. Lunt solar eclipse glasses from B&H Photo Video)

RAIN, RAIN, GO AWAY!

It doesn’t look good for Gulf Tower Fledge Watch this weekend.  As of this writing I have altered the schedule.

Today, Friday May 26:  yes, I’ll make the attempt AFTER NOON.  See you downtown at 1100 Liberty Avenue after the rain stops.  (It’s pouring now.)  Click here for directions.

Saturday May 27:  no

Pittsburgh rain and thunder forecast, 26-27 May 2017 (image as of 26 May from weather.gov with relevant times framed in orange)

Sunday, May 28: yes.  The forecast has changed for the better. See you at Flag Plaza.

Monday, May 29, Memorial Day: yes. See you at Flag Plaza.

(screenshots of the Hourly Weather Forecast for Pittsburgh, PA from weather.gov as of 8am 26 May 2017)

Mild weather during the Cherry Blossom Festival in Washington, D.C., 2006 (photo by Andrew Bossi via Wikimedia Commons)

Ah, the mild days of spring!  You know the days I’m talking about, the ones that are perfect for birding, gardening, picnics and outdoor weddings.  The not-too-hot, not-too-cold, not-too-wet weather that makes you happy to be outdoors.

Unfortunately Pittsburgh will have fewer of them in the future. That’s what scientists from NOAA and Princeton University found out when they studied how the warming climate will affect our pleasant weather.

The loss has begun already though you may not have noticed it. For the last 35 years (1980-2015) earth’s climate has been converting 1 nice day per year into something unpleasant, mostly in Brazil, Africa and the Middle East.

By the end of the century the change will affect us.  The world will lose 10 mild days out of 74 but the loss won’t be evenly distributed.  The tropics will lose even more mild days while Canada, Maine and the Rockies can look forward to a pleasant future.

Here’s what our future looks like on the map.  Notice how the eastern U.S. is light orange indicating a net loss.

Map showing the change in the annual number of mild days across the globe comparing 1986-2005 to 2081-2100. Areas of blue have increased in mild days. Areas of brown see a decline. (Van der Wiel/ NOAA/ Princeton)

That map shows the annual change but in fact it will vary by season.  For instance, Pittsburgh will gain some mild days in the fall (maybe 15) but lose more than that in the summer (25 to 50).  June-to-August will be hot!

Changes in the number of mild weather days by season for 2090 (maps from Van der Wiel/ NOAA/ Princeton)

The full report includes details on mild weather in major cities at: Shifting patterns of mild weather in response to projected radiative forcing.

Now, more than ever, mild weather is a gift.  Enjoy it while you can.

(photo by Andrew Bossi via Wikimedia Commons; click on the image to see the original.
Climate map screenshots from Shifting patterns of mild weather in response to projected radiative forcing)

(*) “Mild weather” is defined as temperatures between 64 and 86 °F, only a trace of rain (less than 0.04 inches) and low humidity (a dewpoint below 68 °F).

Carolina chickadee in North Carolina (photo from Wikimedia Commons)

Last week I wrote about Pittsburgh’s Puzzling Chickadees and promised to tell you why we have fewer black-capped chickadees every year.  The reason is: Our winters are getting warmer.

The Pittsburgh area is squarely in the contact zone where black-capped (Poecile atricapillus) and Carolina chickadees (Poecile carolinensis) meet and hybridize.  Black-capped chickadees can survive cold winters so they live north of the zone.  Carolinas cannot; they live in the south.

The contact zone snakes from New Jersey to Kansas, dipping south along the chilly Appalachian Mountains.  Studies by Robert Curry and his team at Villanova University found that the contact zone is located where winter low temperatures average at or above 14 to 20^oF.

In 2010 David Sibley drew the contact zone for his Distinguishing Black-capped and Carolina Chickadees article. Click on the screenshot to see his original map and zoom it for your area.  The map is about 7 years old.

Screenshot of David Sibley’s map of black-capped and Carolina chickadee contact zone approximately 2010. Click on the map to see Sibley’s original article and zoom the map for your area.

Seven years make a difference.  During that time the zone moved north almost 5 miles.  Here’s why:

Chickadees don’t migrate but young birds disperse to find a breeding territory.  The easiest territory to claim is an “empty” place where there aren’t competing birds of the same species.  For Carolina chickadees, that place is on the northern edge of the contact zone.

In 2000-2002 and 2010-2012, Robert Curry and his team measured winter temperatures and conducted DNA tests to identify chickadees in study plots north, south and inside eastern Pennsylvania’s contact zone.

The studies showed that over the 10-year period winter average low temperatures moved north 0.7 miles per year. They also found that female Carolina chickadees are dispersing further than their usual 0.6 miles.  They’re moving 0.7 miles northward in lock-step with climate change.

What does this mean for you?

If you live on the northern edge of the contact zone your chickadees can change in a year or two from 100% black-capped chickadees to a mix including Carolinas and hybrids.  On the southern edge it’s just as interesting as the black-cappeds disappear.

So don’t take Pittsburgh’s chickadees for granted.  The contact zone is moving northward.

(photo from Wikimedia Commons, map screenshot from David Sibley’s blog: Distinguishing Black-capped and Carolina Chickadees.  Click on each image to see the original.)

Winter sunset at Kuznetsk Alatau, South Siberia (photo from Wikimedia Commons)

By the time you read this, the winter solstice will have passed.

The sun paused it’s southward journey today at 5:44 AM Eastern Time and is already moving north.

Soon the days will be getting longer and the birds will begin to sing.

Listen for the song sparrow.  What day will he sing his first song?

(photo from Wikimedia Commons. click on the image to see the original)