Archive for the 'Weather & Sky' Category

Jan 04 2015

Making Daisies In Outer Space

Published by under Weather & Sky

Precessing Kepler orbit of Earth around the Sun (animation by WillowW on Wikimedia Commons)

Today is the earth’s perihelion, the moment each year when we’re closest to the sun.

Because the earth’s orbit is slightly elliptical, we’re always closest in early January and furthest in July (aphelion), a difference of about 3 million miles.  This sounds like a lot but it’s tiny compared to the size of our orbit.  The distance has no practical effect on our temperature.


When the earth gets close to the sun, the gravitational pull makes us speed up as you can see in the animation.  Right now we’re moving about 1 km/second faster (2,237 mph) than we do in July and this does affect our seasons.  The season surrounding early January (our winter) is 5 days shorter than the season surrounding early July.  This is nice for us but too bad for Australia where their summer is short.

This animation shows our fast and slow progress but its real purpose is to illustrate earth’s orbital precession (in an exaggerated way).

Earth’s orbit is not a closed ellipse.  Instead it tracks out a little further each time as if drawing a huge daisy in outer space without lifting its pencil.  In 21,000 years we come back to where we started and trace the same daisy again.


(animation posted by WillowW on Wikimiedia Commons. Click on the image to see the original with documentation)

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Dec 27 2014

The Cat’s Paw

Published by under Weather & Sky

Cat's Paw Nebula (photo by ESO via Wikimedia Commons)

Seen from the Southern Hemisphere, there’s a cat’s paw in the sky.

The Cat’s Paw Nebula, NGC 6334, was first noted by John Herschel at the Cape of Good Hope in South Africa in 1837.

At -35 degrees declination it’s hard to see this footprint even on a clear night in Pittsburgh.   Cat lovers will have to go south — far south — to get a good look.

This image was taken by the European Southern Observatory (ESO) in Chile.


(photo from ESO via Wikimedia Commons. Click on the image to see the original)

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Dec 21 2014

Winter Solstice

Sunset at frozen Pudasjärvi lake, Finland (photo from Wikimedia Commons)

Today’s going to be a dark day in Pudasjärvi, Finland, where this photo was taken.  Within the next 12 hours, the sun will reach its southern solstice(*).

Pudasjärvi is so far north (at 65° 22′ 39″ N, 26° 55′ 04″ E) that during the winter solstice the sun is up only 3 hours and 30 minutes, rising at 10:27am and setting at 1:58pm.  At high noon it will be only 1.5 degrees above the horizon — barely risen — and to make matters worse the moon is New so it won’t provide any light at all.

The day will be brighter here in Pittsburgh with 9 hours and 17 minutes of sunlight — as soon as the heavy clouds open up and allow the sun to shine.

Starting tomorrow the days will get longer.

Things will get better. I promise!


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

(*) The solstice is at 6:03pm Eastern Standard Time, 1:03am Eastern European Time.

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Dec 20 2014

I Want To See Shadows!

Published by under Weather & Sky

Shadows on Avenue Foch, along the Saint-Roch Square, Le Havre (photo from Wikimedia Commons)

If you live in southwestern Pennsylvania, when’s the last time you saw a shadow outdoors?

A review of weather data for the past 30 days shows the sky has been overcast or foggy every day except for three days near Thanksgiving and on December 7 and December 9.

We’ve had only five days with enough sunlight to make a shadow. Otherwise, we’ve seen only brief glimpses of sun.

Oh for a moment when the clouds are broken! It will finally happen this weekend.  Check the Pittsburgh Clear Sky Chart(*) to see how long it will last.

When the sun comes out, I’m going outdoors to make a shadow of my own.


(photo of Avenue Foch, along the Saint-Roch Square, Le Havre from Wikimedia Commons. Click on the image to see the original.)

(*) Astronomers use the Clear Sky Chart to find out when to view the stars at night.

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Dec 19 2014

Here’s How It Melts

Published by under Weather & Sky

Moulin in Greenland (screenshot from National Geographic video online)

The news was bad this week for the Marshall Islands, South Florida, the Netherlands and Lower Manhattan.

Contrary to earlier predictions, satellite data from Greenland’s ice sheet shows that climate change is melting it a lot faster than we thought.  When all that land-based water melts into the sea, the ocean will rise and permanently flood low-lying land around the world.

Why is it melting so fast?  A big reason is the action of numerous superglacial lakes (i.e. lakes on top of the glacier) that form in the summer. The lakes collect ice melt but they also speed up melting because they empty all at once — downward! — and flow under the ice sheet, lubricating it and sending it much faster to the sea.

If you find this hard to imagine — or even if you don’t — click on the screenshot above (or here) to see a great video showing how this happens.

In the video National Geographic follows a group of scientists camped near a superglacial lake as they studied its development.  One day the lake disappeared, but the weather was so foggy so they couldn’t see what happened. All around them the ice they were standing on cracked and heaved and boomed.  Scary!

When the weather finally cleared they retrieved the measuring devices they’d left on the lake bottom (now no more) and pulled the data.

The lake they’d camped next to — two miles wide and 40 feet deep — had emptied to the ground 3,000 feet below in only 40 minutes!



(screenshot from National Geographic online video.  Click on the image to watch the show)


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Dec 14 2014

Ice Sculptures

Published by under Weather & Sky

Needle ice on a cold morning at Moraine State Park (photo by Kate St.John)

Have you ever seen these ice structures?

Needle ice forms when the soil is still warm and the air is freezing.  As ice forms on the soil’s surface, it draws up subsurface water by capillary action and builds new ice from the bottom.  The result is a structure that looks like needles or tiny barricades. Since there is very little soil above the ice it pokes into the air.

Later in the season when the soil freezes, needle ice forms underground as part of a frost heave.  Click here to see a cut-away frost heave in Vermont.

This patch of needle ice formed above a seep at Moraine State Park last weekend.  Downstream the ground was squishy but here it was forming ice that looked like tiny walls.

Needle ice at Moraine State Park (photo by Kate St. John)

Watch for these ice sculptures on moist soil.


(photos by Kate St. John)

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Dec 07 2014

Chicken In The Sky

Stellar nursery IC 2944 as seen by ESO's Very Large Telescope (photo by ESO)

If our eyes could look deep into space we’d see the clouds in this stellar nursery in the Centaurus constellation, 6,500 light years away.

This pink glowing nebula and clouds of dust were photographed by the European Southern Observatory (ESO) at Cerro Paranal, Chile.  The nebula’s formal name is IC 2944.  Because it’s visible to the naked eye it has a nickname too: The Running Chicken Nebula.

According to ESO’s description, the clouds are Thackeray globules “under fierce bombardment from the ultraviolet radiation from nearby hot young stars.”

Click here or on the image to find out what will happen to the clouds.

If you know where to look on a clear night, you can see a running chicken in the sky.



(photo of stellar nursery IC 2944 by ESO, the European Southern Observatory at Cerro Paranal, Chile. Click on the image to see the original)

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Nov 24 2014

Avoiding The Storm

Red-breasted mergansers (photo by Shawn Collins)

While seven feet of snow fell on parts Buffalo, New York last week, the birds on Lake Erie did their best to avoid the storm.  Because they can fly, it wasn’t hard to do.

The lake effect storm was so localized that it hammered communities south of Buffalo but barely snowed Downtown.  On November 18 Alfonzo Cutaia recorded the amazing wall of white picking up moisture from the lake and carrying it away from Downtown Buffalo.


That night it snowed three inches at Presque Isle State Park in Erie, PA but conditions had improved by the next morning.  Jerry McWilliams described the scene at Sunset Point: “The severe winter storm that was hitting the Buffalo area continued out over the lake until at least 0800 hours [with] heavy storm clouds and whiteout conditions about a mile out on the lake. This may have been the reason for a massive movement of waterfowl this morning, especially Red-breasted Merganser.  Except for Redheads which were mainly moving east, most ducks were moving west.”

Jerry counted 11,400 red-breasted mergansers flying away from the storm.

The ducks escaped but I can only wonder what happened to the songbirds.  I hope they left on Tuesday during the first break in the three-day storm.

And now, as if the snow wasn’t enough, Buffalo has rain, snowmelt, floods and high winds today.

Fly away!


(photo of red-breasted mergansers by Shawn Collins)

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Nov 23 2014

Hot, Cold, or Lukewarm?

Published by under Weather & Sky

Winter temperature outlook 2014-2015 (map from

What’s the weather going to be like this winter?  NOAA’s has a prediction.

If you live in the U.S. West, Alaska, or northern New England, chances are you’ll be warmer than normal.  In the south-central and southeastern U.S. you’ll probably be colder.

But as the map text explains, the white zones aren’t necessarily going to be “normal.”  There’s an equal chance of being hot, cold or lukewarm in Pennsylvania.  We’ll just have to live through it to find out.

Click on the image to read this winter’s prediction at


(Winter temperature outlook 2014-2015 from  Click on the image to see the original)

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Nov 18 2014

Winter Is A Great Pest Control System

Published by under Weather & Sky

Frozen lake in Poland (photo from Wikimedia Commons)

While we brace for 150F this morning and moan that it’s 300F below normal in Pittsburgh, it’s important to look at the bright side.

Last winter’s “polar vortex” put a real dent in invasive insect populations.  It reduced the hemlock woolly adelgid population in the eastern U.S. and completely wiped out adelgids in some of the infected stands in Cook Forest.  It also killed emerald ash borers and stink bugs.

This one-to-two day cold snap won’t seriously reduce invasive insects but it may zap a few bugs caught unexpectedly outside their lairs.  Every little bit helps.

And one more thought in case you aren’t convinced.  There are no poisonous snakes in Alaska and very few in Canada and northern-border U.S. states.

Winter is a great pest control system.   :)


(photo from Wikimedia Commons, Creative Commons license. Click on the image to see the original)

p.s.  It also reduces human pests.  No one’s “partying” at the park across the street from my house.

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